Electrolyte concentration and electrical conductivity of milk: ability to predict lactational mastitis status—A prospective cohort study

Electrolyte concentration and electrical conductivity of milk: ability to predict lactational mastitis status—A prospective cohort study | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Electrolyte concentration and electrical conductivity of milk: ability to predict lactational mastitis status—A prospective cohort study Qian Huang, ZeYu Liu, ShunBo Li, YiMei Tang, Yang Yue, Ying Xiong, and 2 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9142757/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 7 You are reading this latest preprint version Abstract Background Lactational mastitis (LM) is a common and painful postpartum condition. While studies in dairy animals have shown that milk electrolytes and electrical conductivity (EC) can indicate inflammation, human research is scarce. This study compares breast milk electrolyte levels and EC between healthy lactating women and those with LM to improve diagnostic accuracy for this condition. Methods We collected bilateral breast milk from 119 lactating healthy women and 121 women with LM, recorded their clinical characteristics and explored the differences in milk electrolyte concentrations and EC. And then, the self-comparison of conductivity and EC in the inflammation group were recorded, the comparison of mean values in the infected group and the healthy group were conducted. Results indicated differences in electrolyte concentrations and EC between mastitis patients and healthy women. A preliminary optimal cut-off value was established and evaluated for its diagnostic utility in initial LM detection. Results This study included 119 healthy postpartum women and 121 patients with LM. No significant differences in Na⁺, K⁺, Cl⁻, Ca²⁺, or EC were found between left and right breasts in the healthy group. In the LM group, all parameters were significantly higher in affected versus unaffected breasts. All measures were also significantly elevated in the mastitis group compared to the healthy group. Based on these findings, preliminary diagnostic cutoff values were established: Na⁺ (14.300 mmol/L), K⁺ (16.985 mmol/L), Cl⁻ (14.688 mmol/L), Ca²⁺ (6.055 mmol/L), and EC (1.475 mS/cm), offering objective criteria for clinical detection of LM. Conclusions LM incidence is rising and remains a major reason for breastfeeding cessation. Current diagnosis relies on empirical assessment due to the absence of specific diagnostic criteria. Previous animal studies have linked mammary inflammation to alterations in breast milk Na⁺, K⁺, Cl⁻, and Ca²⁺ levels and EC. Our study proposes preliminary cutoff values for these parameters to aid in accurate detection of mammary inflammation, potentially helping to improve breastfeeding continuation rates. Lactational mastitis Milk electrolyte concentration and conductivity quantitative diagnosis Figures Figure 1 BACKGROUND Lactational mastitis (LM) is an inflammatory breast disorder occurring in breastfeeding women, the incidence rate is about 10% in the United States, and it often occurs in the first 3 months postpartum( 1 ). Another study found that it affects approximately 3% to 33% women after delivery( 2 ). The incidence of LM has been increasing year by year, a trend attributed to a combination of social, behavioral, and environmental factors. These include earlier maternal return to work, increased use of breast pumps, suboptimal breastfeeding techniques, and the emergence of antibiotic resistance, among others. LM poses significant risks to both maternal and child health. Its frequent symptomatic presentations are red, tender, hot, and swollen areas of the breast, sometimes, it also shows a painful condition with high fever, flu-like symptoms, for instance chills and aches( 3 , 4 ).Beyond that, approximately 3% of women with LM progress to breast abscess( 5 ), with some studies reporting incidence rates as high as 10%( 6 ). This progression can lead to permanent breast deformity. Beyond causing maternal pain, it often results in breastfeeding cessation, which is responsible for the majority of its adverse effects. A meta-analysis indicated that breastfeeding was inversely associated with the incidence rate of breast cancer, a negative association was also observed between longer breastfeeding durations (vs. shorter durations) and breast cancer risk( 7 ).Another study had observed that each additional 6 months of breastfeeding was associated with a 7% reduction in endometrial cancer risk( 8 ).A protective association was observed between any breastfeeding and invasive ovarian cancer (especially high-grade serous and endometrioid types). Risk reductions were duration-dependent: 18% for 1–3 months per episode and 34% for ≥ 12 months of cumulative breastfeeding( 9 ).For infants, evidence suggests that breastfeeding protects against infections, reduces the incidence of childhood obesity and diabetes, and may modestly enhance cognitive development. However, at present, the diagnosis of LM still relies on clinical symptoms and signs, non-specific laboratory tests. For example, when infection occurs, the affected breast develops a wedge-shaped erythematous area characterized by tenderness, localized heat, and swelling, accompanied by pyrexia and systemic manifestations (such as a temperature above 38.5°C, chills, flu-like aching)( 3 , 4 ).Laboratory tests will typically reveal elevated white blood cell count, neutrophils, and C-reactive protein (CRP). In the absence of typical clinical manifestations and biomarker alterations, clinicians with limited experience may overlook or misdiagnose the condition. By the time these characteristic signs and laboratory abnormalities appear, the disease has often progressed to an advanced stage. Therefore, early-stage quantitative diagnostic methods with high specificity are critical. Accurate identification of LM enables timely clinical intervention, thereby improving prognosis. Therefore, it is particularly important to search for specific quantitative indicators related to LM. As early as the 1960s, Smith et al( 10 ). first documented alterations in milk electrolyte concentrations and electrical conductivity (EC) during bovine LM. By the 1990s, milk EC measurement had been adopted as an experimental screening indicator for mastitis( 11 ). Subsequent animal studies in dairy cows and goats consistently demonstrated increased concentrations of specific ions (notably Na⁺ and Cl⁻) in milk during LM episodes( 12 – 14 ).LM is fundamentally an inflammatory response of mammary tissue( 15 ). During inflammation, cytokines damage local capillaries and parenchyma, disrupting tight junctions between epithelial cells and increasing vascular/alveolar permeability( 16 ). By this same pathological mechanism, when LM occurs in humans, Na⁺ and Cl⁻ (abundant in extracellular fluid) diffuse into the alveolar lumen through compromised tight junctions. To maintain osmotic equilibrium, K⁺ concentrations consequently decrease( 17 ).While milk electrolyte concentration and EC measurements have been widely adopted for detecting LM in veterinary medicine, their efficacy in human clinical practice remains unverified due to a lack of robust studies. This study investigates milk electrolyte concentrations (Na⁺, K⁺, Cl⁻, Ca²⁺) and EC in healthy lactating women and examines their changes during LM, with the objectives of establishing diagnostic cutoff values to differentiate healthy and LM-affected individuals. The findings will facilitate future research on pathogen-specific correlations, disease progression patterns, and potential clinical applications for early antibiotic guidance in LM. METHODS Study subjects All enrolled LM patients were treated at the Department of Breast Surgery, Chengdu Women’s and Children’s Central Hospital, and Pengzhou Maternal and Child Health Hospital between January 2024 and March 2025 (including 91 cases from Chengdu Women’s and Children’s Hospital and 30 cases from Pengzhou Maternal and Child Health Hospital).Our healthy control group consisted of lactating women without breast diseases who visited the same hospitals during the same period (including 89 cases from Chengdu Women’s and Children’s Hospital and 30 cases from Pengzhou Maternal and Child Health Hospital). Inclusion Criteria:1) Aged 18–40 years, 2) Exclusively breastfeeding, 3) Parity ≤ 2, 4) No history of breast diseases (including LM, breast tumors, or trauma), 5) No prior breast surgery (including minimally invasive procedures) or chest wall radiotherapy, 6) No antibiotic use during lactation. Exclusion Criteria: 1) Age 40 years, 2) Non-exclusive breastfeeding, 3) Parity > 2, 4) History of LM, breast neoplasms, or trauma, 5) Prior breast surgery/radiotherapy, 6) Postpartum antibiotic use, 7) Severe cognitive impairment (unable to provide informed consent), 8) Auditory dysfunction affecting compliance. Milk sample collection and Laboratory analysis Sample Collection : 1) pre-collection assessments: Record the age, parity, mode of delivery, and affected breast side (for mastitis group) for all participants,2)timing: a. healthy controls: milk samples collected between 9:00–11:00 AM, excluding the first postpartum week, b. acute mastitis cases: Samples obtained prior to antibiotic administration, 3) sterile protocol: a. disinfected nipple/areolar area (5 cm radius) with iodophor swabs (3–4 wipes), b. discarded initial droplets, c. collected 15 mL per breast using hospital-grade electric pumps, labeled accordingly. Electrolyte/Conductivity Measurement (A-tube samples) :1) environment: 23°C, 55% humidity, 2) Sample preparation: a. low-speed centrifugation: 4,000 rpm × 30 min (4°C), b. collected supernatant → High-speed centrifugation: 13,000 rpm × 15 min (4°C), c. aspirated clear upper layer (minimizing lipid contamination). Analysis :1) electrolytes (Na⁺, K⁺, Cl⁻, Ca²⁺): Measured via auto-calibrated biochemical analyzer, 2) Conductivity: Quantified using calibrated urine analyzer with dedicated cups. The Apparatus and Chemicals used in the experimental procedures are listed in Table 1 . Table 1 Apparatus and Chemicals Used Name Manufacturer Cat.No. Automatic Biochemical Analyzer Hitachi Diagnostic Products Co., Ltd. Labospect-008-AS Automatic Urine Analyzer Dajia Medical Testing Co., Ltd. UC-3500 Hitachi ISE Reference Electrode Solution Hitachi Instruments Co., Ltd. Hitachi ISE Standard Solution (Su 0009-2007) Statistical analysis 1)Excluded objectively unreliable or incomplete records per NCCLS-C28-A2 and Chinese WS/T 402–2012 standards for reference interval establishment, 2) Analytical Methods (SPSS 25.0): descriptive statistics: a. normally distributed data: mean ± SD ( \(\:\stackrel{-}{x}\) ± s), b. non-normal data: median (P25, P75), c. categorical data: n (%). Inferential statistics: a. normally distributed variables: Independent t-test, b. non-normal variables: Mann-Whitney U test, c. Parity (healthy vs. mastitis groups): χ² test (R×C contingency table),3. Optimal cutoff values (Na⁺, K⁺, Cl⁻, Ca²⁺, EC): ROC-derived, validated by χ² test, 4) Significance threshold: Two-tailed p < 0.05. RESULTS 1.General Characteristics This study included 119 healthy lactating women (119 cases) and 121 patients with LM (121 cases). The healthy group had a mean age of 28.53 ± 3.67 years (range: 22–38), while the mastitis group averaged 29.30 ± 3.29 years (range: 22–38). Both groups had parity ranging from 1 to 2 deliveries, with 103 cases (86.55%) being primiparous and 16 cases (13.45%) multiparous in the healthy group, compared to 107 primiparous (88.43%) and 14 multiparous (11.57%) cases in the mastitis group. Regarding delivery mode, the healthy group included 87 vaginal deliveries (73.11%) and 32 cesarean sections (26.89%), whereas the mastitis group had 92 vaginal deliveries (76.03%) and 29 cesarean sections (23.97%). In the mastitis group, the affected breast was left-sided in 69 cases (57.02%) and right-sided in 52 cases (42.98%) (Table 2 − 1). Table 2.1 General Characteristics Age in year Mastitis group(n = 121) Healthy group(n = 119) 29.30(22,38) 28.53(22,38) Parity 1(107, 88.43%) 2(14,11.57%) 1(103,86.55%) 2(16, 13.45%) Delivery mode Vaginal delivery: (92, 76.03%) Cesarean section: (29, 23.97%) Vaginal delivery: (87, 73.11%) Cesarean section: (32, 26.89%) Breast laterality in mastitis cases - Left:69(57.02%) Right:52(42.98%) No significant differences were observed between groups regarding age, parity, or delivery mode (all p > 0.05, Table 2 – 2 ). Table 2 2 Comparison of Baseline Characteristics Group Age in year Parity Delivery mode Breast laterality in mastitis cases Healthy group 28.53 ± 3.67 1(86.55%) 2(13.45%) Vaginal delivery: 87(73.11%) Cesarean section: 32(26.89%) - Mastitis group 29.30 ± 3.29 1(88.43%) 2(11.57%) Vaginal delivery: 92(76.03%) Cesarean section: 29(23.97%) Left:57.02% Right:42.98% p -Value 0.089 0.662 0.603 - 2.Comparison of Electrolyte Concentrations and EC Between Bilateral Breasts in Healthy Lactating Women The Shapiro-Wilk test for normality showed that the concentrations of Na + , K + , Cl − , Ca 2+ , and EC in the breast milk of the healthy group did not follow a normal distribution ( p <0.05). Therefore, the Mann-Whitney U test (a nonparametric test for two independent samples) was used to compare the experimental data of bilateral breast milk Na + , K + , Cl − , Ca 2+ concentrations, as well as EC in the healthy group. In the healthy group, the left breast milk Na + , K + , Cl − , Ca 2+ concentrations, and EC were11.70 (9.90, 13.40) mmol/L, 13.50 (11.80, 16.05) mmol/L, 13.80 (12.00, 15.30) mmol/L, 5.56 (4.90, 6.18) mmol/L, and 1.40 (1.00, 1.90) µS/cm, respectively. The right breast milk Na + , K + , Cl − , Ca 2+ concentrations, and EC were 11.10 (9.10, 12.50) mmol/L, 14.30 (11.94, 14.91) mmol/L, 13.40 (11.80, 15.30) mmol/L, 5.53 (4.89, 6.10) mmol/L, and 1.3 (0.80, 1.70) µS/cm, respectively. No statistically significant differences were observed between the left and right breast milk Na + , K + , Cl − , Ca 2+ concentrations, or EC in the healthy group ( p > 0.05) (see Table 3 ). Table 3 Comparison of bilateral breast milk electrolyte concentrations and electrical conductivity in the healthy group Group Na + (mmol/L) K + (mmol/L) Cl - (mmol/L) Ca 2+ (mmol/L) EC(µS/cm) Left 11.70 (9.90, 13.40) 13.50 (11.80,16.05) 13.80 (12.00, 15.30) 5.56 (4.90,6.18) 1.4 (1.0,1.90) Right 11.10 (9.10, 12.50) 14.3 (11.94,14.91) 13.40 (11.80, 15.30) 5.53 (4.89,6.10) 1.3 (0.80,1.70) Z-score -2.645 -1.292 -1.786 -1.134 -0.214 p -Value 0.08 0.196 0.074 0.257 0.813 3.Comparison of Electrolyte Concentrations and EC Between Affected and Unaffected Breasts in LM Patients This study analyzed 121 cases of LM, comparing electrolyte concentrations and EC between affected and unaffected breasts. The Shapiro-Wilk test confirmed non-normal distribution for all parameters (Na + , K + , Cl - , Ca 2+ concentrations and EC; p < 0.05), necessitating use of the Wilcoxon signed-rank test. Significant differences were observed between affected and unaffected breasts. Affected breasts showed elevated Na + (12.50 [7.90–16.1] vs 7.80 [7.20-13.25] mmol/L), K + (17.82 [14.3–18.80] vs 13.34 [10.58–15.49] mmol/L), Cl - (13.30 [11.60–17.80] vs 11.60 [8.90–14.10] mmol/L), Ca 2+ (5.80 [5.42–6.47] vs 5.57 [4.88–6.36] mmol/L), and EC (1.90 [1.40–2.40] vs 1.20 [0.90–1.40] µS/cm). All differences were statistically significant ( p < 0.05), demonstrating consistent elevation of these parameters in affected breasts compared to unaffected controls (Table 4 ). Table 4 Comparison of Electrolyte Concentrations and EC Between Affected and Unaffected Breasts in LM Patients Group Na + (mmol/L) K + (mmol/L) Cl - (mmol/L) Ca 2+ (mmol/L) EC(µS/cm) Affected Side 12.50 (7.90,16.1) 17.82 (14.3,18.80) 13.30 (11.60,17.80) 5.80 (5.42,6.47) 1.90 (1.40,2.40) Unaffected Side 7.80 (7.20,13.25) 13.34 (10.58,15.49) 11.60 (8.90,14.10) 5.57 (4.88,6.36) 1.20 (0.90,1.40) Z-Score -4.683 -7.700 -4.429 -2.904 -7.276 p -Value <0.05 <0.05 <0.05 <0.05 <0.05 4.Comparison of electrolyte concentrations and EC in breast milk between healthy and mastitis-affected groups As the breast milk electrolyte concentrations and EC data from both healthy and mastitis groups showed non-normal distribution (Shapiro-Wilk test, p < 0.05), the Mann-Whitney U test was used for statistical analysis. For the healthy group, the average values of bilateral breast milk measurements were used for comparison with the affected side of mastitis patients. The mastitis group comprised 121 patients (121 samples). The healthy group showed the following median (IQR) values: Na + concentration 11.00 (9.30,13.10) mmol/L, K + concentration 13.56 (11.87,15.66) mmol/L, Cl − concentration 11.98 (11.15,13.99) mmol/L, Ca 2+ concentration 5.44 (4.97,6.02) mmol/L, and EC1.35 (1.0,1.70) µS/cm. In comparison, the mastitis-affected side demonstrated: Na + 12.50 (7.90,16.10) mmol/L, K + 17.82 (14.30,18.80) mmol/L, Cl − 13.30 (11.60,17.8) mmol/L, Ca 2+ 5.80 (5.42,6.47) mmol/L, and EC 1.90 (1.40,2.40) µS/cm. Comparison of breast milk Na + , K + , Cl − , and Ca 2+ concentrations and EC between the healthy group and affected side of the mastitis group showed statistically significant differences in all measured parameters ( p < 0.05), with higher values observed in the mastitis group compared to the healthy group (Table 5 ). Table 5 Comparison of electrolyte concentrations and EC between healthy group and affected side of LM Group Na + (mmol/L) K + (mmol/L) Cl - (mmol/L) Ca 2+ (mmol/L) EC(µS/cm) Healthy Group 11.00 (9.30,13.10) 13.56 (11.87,15.66) 11.98 (11.15,13.99) 5.44 (4.97,6.02) 1.35 (1.0,1.70) Mastitis Group 12.50 (7.90,16.10) 17.82 (14.30,18.80) 13.30 (11.60,17.8) 5.80 (5.42,6.47) 1.90 (1.40,2.40) Z-Score -2.890 -7.574 -4.500 -5.696 -3.581 p -Value <0.05 <0.05 <0.05 <0.05 <0.05 5 Diagnostic Thresholds for LM: Electrolyte Concentrations and EC Optimal Cut-off Values 5.1 ROC Curve Analysis for Milk Electrolyte Concentrations and EC in Lactational Mastitis The Na + , K + , Cl - , and Ca 2+ concentrations and EC in breast milk from the affected side of LM patients showed statistically significant differences compared to healthy controls. Using the Diagnosis and Treatment Guidelines for Lactational Mastitis in China as the diagnostic standard, we constructed ROC curves for all parameter (Figs. 1 ). The analysis revealed significant diagnostic performance for all measures: Na + concentration showed an AUC of 0.608 (95% CI: 0.533–0.683, p < 0.05), K + concentration 0.783 (95% CI: 0.724–0.842, p < 0.05), Cl - concentration 0.634 (95% CI: 0.561–0.707, p < 0.05), Ca 2+ concentration 0.668 (95% CI: 0.600-0.736, p < 0.05), and EC 0.713 (95% CI: 0.648–0.777, p < 0.05). Receiver operating characteristic (ROC) curves illustrating the sensitivity and specificity of sodium ions (Na⁺), potassium ions (K⁺), chloride ions (Cl⁻), calcium ions (Ca²⁺), and electrical conductivity (EC) in differentiating between affected and unaffected breasts. The diagonal reference line (dashed) represents no discriminatory ability (AUC = 0.5). AUC, area under the curve. 5.1 Calculate the Optimal Cutoff Values for Na⁺, K⁺, Cl⁻, and Ca²⁺, as well as EC The Youden index (sensitivity+specificity-1) was calculated to determine optimal cutoff values for Na⁺ concentration, K⁺ concentration, Cl⁻ concentration, Ca²⁺ concentration, and EC. The maximum Youden indices were 0.329, 0.536, 0.387, 0.328, and 0.391 for Na⁺ concentration, K⁺ concentration, Cl⁻ concentration, Ca²⁺ concentration, and EC, respectively. The corresponding optimal cutoff values were 14.300 mmol/L for Na⁺ concentration, 16.985 mmol/L for K⁺ concentration, 14.688 mmol/L for Cl⁻ concentration, 6.055 mmol/L for Ca²⁺ concentration, and 1.475 µS/cm for EC. 5.2 The Optimal Cutoff Values for Na⁺ concentration, Cl⁻ concentration, and EC were Further Validated Using Chi-square (χ²) tests. Using cutoff values of 14.300 mmol/L for Na⁺ concentration, 16.985 mmol/L for K⁺ concentration, 14.688 mmol/L for Cl⁻ concentration, 6.055 mmol/L for Ca²⁺ concentration, and 1.475 µS/cm for EC, patients were stratified into healthy and mastitis groups. Chi-square tests revealed statistically significant differences between groups for all cutoff parameters (Na⁺: χ²=32.527, p < 0.05; K⁺: χ²=80.377, p < 0.05; Cl⁻: χ²=10.660, p < 0.05; Ca²⁺: χ²=29.010, p < 0.05; conductivity: χ²=37.033, p < 0.05) (Table 6 ). Table 6 Diagnostic Thresholds for Lactational Mastitis: Electrolyte Concentrations and Conductivity Optimal Cut-off Values Parameter Cut-off Value AUC (95% CI) Sensitivity Specificity χ²-Score p -value Na + 14.300 0.608 (0.533–0.683) 43.80% 89.10% 32.527 < 0.05 K + 16.985 0.783 (0.724–0.842) 57.90% 95.80% 80.377 < 0.05 Cl - 14.688 0.634 (0.561–0.707) 45.50% 93.30% 10.660 < 0.05 Ca 2+ 6.055 0.668 (0.600-0.736) 49.60% 83.20% 29.010 < 0.05 EC 1.475 0.713 (0.648–0.777) 74.40% 64.70% 37.033 < 0.05 DISCUSSION LM negatively impacts maternal and infant health, but its diagnosis remains reliant on nonspecific clinical signs and symptoms. Recent pathological findings underscore the need for objective biomarkers. This study analyzes electrolyte concentrations and EC in processed breast milk samples to investigate their correlation with LM, aiming to establish a theoretical basis for more specific diagnostic methods. Mechanisms underlying altered Na + , Cl − levels and EC in inflamed breast milk. The differences in Na + , Cl − concentrations and EC between affected/unaffected breasts in LM patients, and between healthy lactating women and LM patients, may be closely associated with LM pathogenesis. Two distinct hypotheses exist regarding the pathogenesis of LM. The infectious theory posits that it is primarily a microbial disease, supported by cultured pathogens such as Staphylococcus aureus, Escherichia coli, and Streptococcus spp. from milk samples using advanced bacteriological techniques( 18 ).Staphylococcus epidermidis, a commensal bacterium colonizing human skin and mucous membranes, has recently been identified in milk samples from LM cases, suggesting its potential role as an emerging pathogen in this condition( 19 – 21 ).These findings historically supported the classification of LM as an infectious disease. However, emerging research has led some scholars to challenge this simplistic etiological framework( 22 ).This leads to an alternative hypothesis, proposing LM as primarily an inflammatory disorder. Regardless of whether LM is classified as an infectious or inflammatory disease, its molecular mechanisms are closely linked to Toll-like receptor (TLR) signaling pathways—either triggered by microbe-associated molecular patterns (MAMPs) or damage-associated molecular patterns (DAMPs). The pathogenesis of infectious LM may involve the MAMP-mediated TLR signaling pathway. Among the pattern recognition receptors (PRRs), TLR2, TLR4 and TLR5 specifically recognize bacterial components such as lipoteichoic acid, lipopolysaccharide, flagellin and bacterial lipopeptides. Upon binding to these MAMPs, TLRs transduce extracellular signals into the cell, leading to activation of the transcription factor NF-κB. This subsequently triggers transcriptional and translational processes that result in the release of various inflammatory cytokines, chemokines and adhesion molecules, while simultaneously recruiting other innate immune components such as neutrophils to the site of infection( 23 ). In the absence of pathogenic bacteria, host-derived DAMPs can activate TLRs through sterile inflammatory pathways( 24 , 25 ). DAMPs promote inflammatory responses via two distinct mechanisms: 1) Direct activation of inflammatory mediators that subsequently trigger TLRs and downstream NF-κB signaling( 26 ), and 2) Potentiation of TLR-mediated immune responses in sterile environments through positive feedback amplification of TLR/NF-κB activation, ultimately contributing to the development of inflammatory lactational mastitis( 27 ). The inflammatory cytokines induced through two distinct signaling pathways trigger pathological changes in mammary tissue, including damage to capillary walls and glandular acini, thereby increasing epithelial permeability( 16 ). This leads to altered milk composition. During inflammatory conditions, cytokines disrupt tight junctions between acinar cells and enhance capillary permeability, allowing elevated Na + and Cl − from extracellular fluid to enter the mammary gland acinar cavity. Consequently, during LM, concentrations of certain ions (e.g., Na + and Cl − ) increase in breast milk—a finding consistent with prior animal studies and our results( 28 ).Milk conductivity is primarily determined by its ionic composition (Na + , K + , Cl − ), as centrifugation excludes interference from organic components (e.g., fat, proteins). Thus, the LM-induced elevation in Na + and Cl − concentrations directly contributes to increased EC. Another school of thought suggests that under inflammatory conditions, the decreased lactose content in milk triggers a compensatory increase in Na + and Cl − concentrations to maintain osmotic equilibrium with plasma, a finding consistent with our results. Mechanisms Underlying Altered K + Concentrations in LM Milk Compared to Healthy Controls Wegner et al. ( 29 )investigated 56 Holstein cows to evaluate mastitis using milk electrolyte concentrations and EC as diagnostic indicators. Their findings revealed that LM milk exhibited significantly elevated Na + and Cl − concentrations along with decreased K + levels compared to healthy controls, accompanied by altered EC values. Our data demonstrate elevated milk K⁺ levels in mastitis-affected breasts compared to healthy controls (healthy: 13.56 (11.87,15.66) mmol/L vs. inflammatory: 17.82 (14.30,18.80) mmol/L), contrasting with bovine studies typically reporting decreased K⁺ during mastitis. This adverse finding may be attributed to two potential mechanisms: 1) necrosis of mammary alveolar epithelial cells releasing intracellular K + into the mammary gland acinar cavity, thereby counteracting the LM-induced K + reduction; and 2) inflammatory cytokine-mediated impairment of Na + /K + -ATPase pump efficiency, reducing K + influx. However, the exact underlying mechanisms require further investigation. Mechanisms Underlying Altered Ca Concentrations in LM Milk Compared to Healthy Controls Dalal et al.( 30 ) demonstrated that Ca²⁺ signaling in endothelial cells serves as a critical regulatory mechanism for inflammatory responses. Their work revealed that inflammation-mediated Ca²⁺ influx leads to decreased serum Ca²⁺ concentrations, suggesting systemic Ca²⁺ redistribution during immune activation. Previous animal studies have suggested that decreased milk Ca²⁺concentrations reflect inflammatory status, a finding inconsistent with our results. This discrepancy may be attributed to dual mechanisms in LM: 1) inflammation-induced extracellular Ca 2+ influx, coupled with 2) cytokine-mediated increases in capillary and mammary alveolar permeability, which collectively facilitate diffusion of high-concentration extracellular Ca 2+ into the mammary acini. These compensatory processes may maintain or elevate Ca 2+ concentrations in milk despite the inflammatory milieu. Additionally, macromolecular components in milk may influence ionic calcium levels. For instance, casein - whose production decreases during inflammatory states due to impaired mammary synthetic capacity - normally binds ionic calcium. The reduction in casein content could consequently lead to increased free ionic Ca 2+ concentrations in milk. Methodological differences may further explain the discrepancy with prior animal studies. While previous research employed real-time electrolyte measurements, our protocol required sample preprocessing, suggesting that variations in measurement standards may affect result comparability. Furthermore, species-specific differences in Ca 2+ homeostasis may exist between humans and dairy cows during LM. The underlying regulatory mechanisms remain to be elucidated through further investigation. Diagnostic Thresholds of Na⁺, K⁺, Cl⁻, Ca²⁺ Concentrations and EC in LM This study preliminarily established optimal cutoff values for Na⁺ (14.300 mmol/L), K⁺ (16.985 mmol/L), Cl⁻ (14.688 mmol/L), and Ca²⁺ (6.055 mmol/L) concentrations, along with EC (1.475 µS/cm) in breast milk, demonstrating significant discriminative ability between healthy lactating women and those with LM. The corresponding receiver operating characteristic curve analysis yielded area under the curve values of 0.608 (95% CI: 0.533–0.683, P < 0.05) for Na⁺, 0.783 (95% CI: 0.724–0.842, P < 0.05) for K⁺, 0.634 (95% CI: 0.561–0.707, P < 0.05) for Cl⁻, 0.668 (95% CI: 0.600-0.736, P < 0.05) for Ca²⁺, and 0.713 (95% CI: 0.648–0.777, P < 0.05) for EC, all showing statistically significant diagnostic performance. These findings provide important evidence for establishing noninvasive and objective diagnostic criteria in clinical practice for LM. Limitations and Future Directions This study has several limitations that should be acknowledged. First and foremost, although the methods used to measure breast milk electrolytes and EC represent the gold standard for clinical serum electrolyte analysis and urinary EC measurement, they have not undergone comprehensive methodological validation for the complex matrix of human milk. The lack of systematic data on recovery rates, interference tests, and dilution linearity means that potential matrix effects on absolute accuracy cannot be ruled out. Second, due to equipment constraints and the absence of dedicated instruments for human milk, our instrumental setup, though chosen after expert consultation, may have inherent limitations for this specific application. Despite these limitations, we employed rigorous internal quality controls, standardized processing, and internal consistency checks (e.g., bilateral similarity in healthy participants) to bolster the reliability of our comparative findings. The significant differences observed between groups align with pathophysiology and support the method's discriminative capability. This study is an exploratory investigation in the field of human milk, building upon prior findings from mammalian research. Future studies should prioritize conducting matrix-specific validation before applying the methodology. Furthermore, developing or optimizing dedicated instruments for human milk analysis and conducting larger, multicenter cohort studies would be crucial for confirming and extending the findings of this research. CONCLUSION Pathological alterations in LM lead to significant changes in milk electrolyte concentrations and EC. Diagnostic thresholds of Na + ≥14.300 mmol/L, K + ≥16.985 mmol/L, Cl − ≥14.688 mmol/L, Ca 2+ ≥6.055 mmol/L, or EC ≥ 1.475µS/cm indicate localized mammary inflammation. These objective quantitative criteria provide clinicians with an evidence-based alternative to empirical diagnosis, which may help reduce unnecessary antibiotic use during LM and ultimately improve breastfeeding continuation rates. Furthermore, our study provides conclusive evidence that milk production is significantly impaired in inflamed mammary glands. While our current study has elucidated the differential patterns of milk electrolyte concentrations and EC between healthy lactating women and those with LM, future research will focus on: 1) the correlation between these biochemical parameters and specific microbial etiologies of LM, 2) their dynamic changes across different stages of disease progression, and 3) exploring the long-term effects of LM on maternal and infant health. This systematic approach will establish a comprehensive evidence base regarding the pathophysiological relationships between milk physicochemical properties and LM pathogenesis. Abbreviations LM Lactational mastitis EC Electrical conductivity CRP C-reactive protein TLR Toll-like receptor MAMPs Microbe-associated molecular patterns DAMPs Damage-associated molecular patterns PRRs Pattern recognition receptors Declarations Ethical approval This study was approved by The Institutional Review Board of Chengdu Women's and Children's Central Hospital (reference number2023[30]) and The Ethics Committee of Pengzhou Maternal and Child Health Hospital (reference number2023[001]). Informed consent was obtained from all participants prior to enrollment. And all authors could ensure the confidentiality of patient data. The study followed the latest version of the Helsinki Declaration. Consent for publication Not applicable. Availability of data and materials The datasets analysed during the current study are available from the corresponding author on reasonable request. Competing interests The authors declare that they have no competing interests. Funding The funding for this study was provided by the Chengdu Municipal Health Commission, China, through the project titled "A Prospective Cohort Study on Diagnosing Early Lactation Mastitis Based on Breast Milk Electrolyte Concentrations and Electrical Conductivity" (Project No. 2023311). Authors’ contributions Q.H. and P.N. conceived and designed the study. Q.H. and Y.M.T. wrote the first draft of the manuscript. S.B.L, Y.M.T., Z.Y.L., Y.Y. ,Y,D.,Y.X. performed sample collection, preparation and data gathering. S.B.L., Q.H.,Z.Y.L. analyzed the data, interpreted the results. All authors read and approved the final manuscript. Acknowledgements Not applicable. References Morcomb EF, Dargel CM, Anderson SA, Mastitis. Rapid Evid Rev Am Fam Physician. 2024;110(2):174–82. Lai BY, Yu BW, Chu AJ, Liang SB, Jia LY, Liu JP, et al. Risk factors for lactation mastitis in China: A systematic review and meta-analysis. PLoS ONE. 2021;16(5):e0251182. Cooney F, Petty-Saphon N. The Burden of Severe Lactational Mastitis in Ireland from 2006 to 2015. Ir Med J. 2019;112(1):855. Amir LH. ABM clinical protocol #4: Mastitis, revised March 2014. Breastfeed Med. 2014;9(5):239–43. O'Brien C, Quinn E, Murphy M, Lehane E, O'Leary DP, Livingstone V, et al. Breast abscess: Not just a puerperal problem. Breast J. 2020;26(2):339–42. Amir LH, Forster D, McLachlan H, Lumley J. Incidence of breast abscess in lactating women: report from an Australian cohort. BJOG. 2004;111(12):1378–81. Zhou Y, Chen J, Li Q, Huang W, Lan H, Jiang H. Association between breastfeeding and breast cancer risk: evidence from a meta-analysis. Breastfeed Med. 2015;10(3):175–82. Ma X, Zhao LG, Sun JW, Yang Y, Zheng JL, Gao J, et al. Association between breastfeeding and risk of endometrial cancer: a meta-analysis of epidemiological studies. Eur J Cancer Prev. 2018;27(2):144–51. Babic A, Sasamoto N, Rosner BA, Tworoger SS, Jordan SJ, Risch HA, et al. Association Between Breastfeeding and Ovarian Cancer Risk. JAMA Oncol. 2020;6(6):e200421. Smith A, Wheelock JV, Dodd FH. Effect of milking throughout pregnancy on milk yield in the succeeding lactation. J Dairy Sci. 1966;49(7):895–6. Musser JM, Anderson KL, Caballero M, Amaya D, Maroto-Puga J. Evaluation of a hand-held electrical conductivity meter for detection of subclinical mastitis in cattle. Am J Vet Res. 1998;59(9):1087–91. Prosser CG, Hartmann PE. Comparison of mammary gland function during the ovulatory menstrual cycle and acute breast inflammation in women. Aust J Exp Biol Med Sci. 1983;61(Pt 3):277–86. Semba RD. Mastitis and transmission of human immunodeficiency virus through breast milk. Ann N Y Acad Sci. 2000;918:156–62. Reviews of Physiology. Biochemistry and Pharmacology. Anticancer Res. 2016;36(9):4980. Omranipour R, Vasigh M, Mastitis. Breast Abscess, and Granulomatous Mastitis. Adv Exp Med Biol. 2020;1252:53–61. Fetherston CM, Lai CT, Hartmann PE. Relationships between symptoms and changes in breast physiology during lactation mastitis. Breastfeed Med. 2006;1(3):136–45. Prentice A, Prentice AM, Lamb WH. Mastitis in rural Gambian mothers and the protection of the breast by milk antimicrobial factors. Trans R Soc Trop Med Hyg. 1985;79(1):90–5. Rimoldi SG, Pileri P, Mazzocco MI, Romeri F, Bestetti G, Calvagna N, et al. The Role of Staphylococcus aureus in Mastitis: A Multidisciplinary Working Group Experience. J Hum Lact. 2020;36(3):503–9. Berens P, Swaim L, Peterson B. Incidence of methicillin-resistant Staphylococcus aureus in postpartum breast abscesses. Breastfeed Med. 2010;5(3):113–5. Rodvold KA, McConeghy KW. Methicillin-resistant Staphylococcus aureus therapy: past, present, and future. Clin Infect Dis. 2014;58(Suppl 1):S20–7. Lasagno M, Ortiz M, Vissio C, Yaciuk R, Bonetto C, Pellegrino M, et al. Pathogenesis and inflammatory response in experimental caprine mastitis due to Staphylococcus chromogenes. Microb Pathog. 2018;116:146–52. Kvist LJ, Larsson BW, Hall-Lord ML, Steen A, Schalén C. The role of bacteria in lactational mastitis and some considerations of the use of antibiotic treatment. Int Breastfeed J. 2008;3:6. Kawai T, Akira S. The role of pattern-recognition receptors in innate immunity: update on Toll-like receptors. Nat Immunol. 2010;11(5):373–84. McDermott MF, Tschopp J. From inflammasomes to fevers, crystals and hypertension: how basic research explains inflammatory diseases. Trends Mol Med. 2007;13(9):381–8. Buchanan MM, Hutchinson M, Watkins LR, Yin H. Toll-like receptor 4 in CNS pathologies. J Neurochem. 2010;114(1):13–27. El Mezayen R, El Gazzar M, Seeds MC, McCall CE, Dreskin SC, Nicolls MR. Endogenous signals released from necrotic cells augment inflammatory responses to bacterial endotoxin. Immunol Lett. 2007;111(1):36–44. Samuvel DJ, Sundararaj KP, Nareika A, Lopes-Virella MF, Huang Y. Lactate boosts TLR4 signaling and NF-kappaB pathway-mediated gene transcription in macrophages via monocarboxylate transporters and MD-2 up-regulation. J Immunol. 2009;182(4):2476–84. Semba RD, Kumwenda N, Taha TE, Hoover DR, Lan Y, Eisinger W, et al. Mastitis and immunological factors in breast milk of lactating women in Malawi. Clin Diagn Lab Immunol. 1999;6(5):671–4. Wegner TN, Stull JW. Relation between mastitis test score, mineral composition of milk, and blood electrolyte profiles in Holstein cows. J Dairy Sci. 1978;61(12):1755–9. Dalal PJ, Muller WA, Sullivan DP. Endothelial Cell Calcium Signaling during Barrier Function and Inflammation. Am J Pathol. 2020;190(3):535–42. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Under Review Version 1 posted Reviews received at journal 16 Apr, 2026 Reviewers agreed at journal 07 Apr, 2026 Reviewers invited by journal 07 Apr, 2026 Editor invited by journal 18 Mar, 2026 Editor assigned by journal 18 Mar, 2026 Submission checks completed at journal 18 Mar, 2026 First submitted to journal 16 Mar, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-9142757","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":620571005,"identity":"9d1d5819-cf58-4be1-bb82-5c540bf0fa0c","order_by":0,"name":"Qian Huang","email":"","orcid":"","institution":"Chengdu Women's and Children's Central Hospital, University of Electronic Science and Technology of China","correspondingAuthor":false,"prefix":"","firstName":"Qian","middleName":"","lastName":"Huang","suffix":""},{"id":620571009,"identity":"fe7dbfe2-e7b9-4cba-b5fd-9add0befe763","order_by":1,"name":"ZeYu Liu","email":"","orcid":"","institution":"Chengdu Women's and Children's Central Hospital, University of Electronic Science and Technology of China","correspondingAuthor":false,"prefix":"","firstName":"ZeYu","middleName":"","lastName":"Liu","suffix":""},{"id":620571014,"identity":"f6bfe44c-63d9-435d-a94e-20b0e4da0fee","order_by":2,"name":"ShunBo Li","email":"","orcid":"","institution":"Chengdu Women's and Children's Central Hospital, University of Electronic Science and Technology of China","correspondingAuthor":false,"prefix":"","firstName":"ShunBo","middleName":"","lastName":"Li","suffix":""},{"id":620571019,"identity":"d97d33fc-dc86-4d7c-80bf-0f487725c402","order_by":3,"name":"YiMei Tang","email":"","orcid":"","institution":"Chengdu Women's and Children's Central Hospital, University of Electronic Science and Technology of China","correspondingAuthor":false,"prefix":"","firstName":"YiMei","middleName":"","lastName":"Tang","suffix":""},{"id":620571023,"identity":"a646ff3d-33e7-4d22-b084-c3408e6d8fd4","order_by":4,"name":"Yang Yue","email":"","orcid":"","institution":"Pengzhou Maternal and Child Health Hospital","correspondingAuthor":false,"prefix":"","firstName":"Yang","middleName":"","lastName":"Yue","suffix":""},{"id":620571027,"identity":"7b203244-0033-4e01-a04c-7ed0006a53e1","order_by":5,"name":"Ying Xiong","email":"","orcid":"","institution":"Chengdu Women's and Children's Central Hospital, University of Electronic Science and Technology of China","correspondingAuthor":false,"prefix":"","firstName":"Ying","middleName":"","lastName":"Xiong","suffix":""},{"id":620571030,"identity":"15c7b5f5-32d3-4469-9268-af015182afdb","order_by":6,"name":"Yuan Deng","email":"","orcid":"","institution":"Chengdu Women's and Children's Central Hospital, University of Electronic Science and Technology of China","correspondingAuthor":false,"prefix":"","firstName":"Yuan","middleName":"","lastName":"Deng","suffix":""},{"id":620571032,"identity":"da7a9470-e44d-4964-9fa9-8dafa110a74a","order_by":7,"name":"Ping Ning","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAs0lEQVRIiWNgGAWjYFACxgYGBgMJOTb29gOkaCmwMObjOZNAik0fKhLnSTgYEKfYXLq57eEXA4n0NgmGBIYfFdsIa7Gcc7DdWMZAIrdNuvEAY8+Z24S1GNxIbJOWAGmROZDAzNhGgpZ0NokEA+K1SH4wkEggQcudg23SwHgxbAMG8kHi/HK7/Znkjz918vLt7Qcf/KggQguDBAMDMw+UfYAI9RAtjD+IUzoKRsEoGAUjFQAARFE6aCnzN/wAAAAASUVORK5CYII=","orcid":"","institution":"Chengdu Women's and Children's Central Hospital, University of Electronic Science and Technology of China","correspondingAuthor":true,"prefix":"","firstName":"Ping","middleName":"","lastName":"Ning","suffix":""}],"badges":[],"createdAt":"2026-03-17 01:53:19","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9142757/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9142757/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":106871626,"identity":"5d60308c-3fd3-4def-a32c-d87b184890d0","added_by":"auto","created_at":"2026-04-14 09:49:45","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":78021,"visible":true,"origin":"","legend":"\u003cp\u003eDiagnostic performance of electrolyte concentrations and electrical conductivity (EC) for lactational mastitis (LM).\u003c/p\u003e\n\u003cp\u003eReceiver operating characteristic (ROC) curves illustrating the sensitivity and specificity of sodium ions (Na⁺), potassium ions (K⁺), chloride ions (Cl⁻), calcium ions (Ca²⁺), and electrical conductivity (EC) in differentiating between affected and unaffected breasts. The diagonal reference line (dashed) represents no discriminatory ability (AUC = 0.5). AUC, area under the curve.\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-9142757/v1/60fe8458a774ef28c5da82d0.png"},{"id":106961383,"identity":"ec9add1e-864a-48ed-b56b-abee37981329","added_by":"auto","created_at":"2026-04-15 09:25:22","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1443179,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9142757/v1/5a3123ee-e1fe-41ad-b501-db71701ac174.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Electrolyte concentration and electrical conductivity of milk: ability to predict lactational mastitis status—A prospective cohort study","fulltext":[{"header":"BACKGROUND","content":"\u003cp\u003eLactational mastitis (LM) is an inflammatory breast disorder occurring in breastfeeding women, the incidence rate is about 10% in the United States, and it often occurs in the first 3 months postpartum(\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e). Another study found that it affects approximately 3% to 33% women after delivery(\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e). The incidence of LM has been increasing year by year, a trend attributed to a combination of social, behavioral, and environmental factors. These include earlier maternal return to work, increased use of breast pumps, suboptimal breastfeeding techniques, and the emergence of antibiotic resistance, among others. LM poses significant risks to both maternal and child health. Its frequent symptomatic presentations are red, tender, hot, and swollen areas of the breast, sometimes, it also shows a painful condition with high fever, flu-like symptoms, for instance chills and aches(\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e).Beyond that, approximately 3% of women with LM progress to breast abscess(\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e), with some studies reporting incidence rates as high as 10%(\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e). This progression can lead to permanent breast deformity. Beyond causing maternal pain, it often results in breastfeeding cessation, which is responsible for the majority of its adverse effects. A meta-analysis indicated that breastfeeding was inversely associated with the incidence rate of breast cancer, a negative association was also observed between longer breastfeeding durations (vs. shorter durations) and breast cancer risk(\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e).Another study had observed that each additional 6 months of breastfeeding was associated with a 7% reduction in endometrial cancer risk(\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e).A protective association was observed between any breastfeeding and invasive ovarian cancer (especially high-grade serous and endometrioid types). Risk reductions were duration-dependent: 18% for 1\u0026ndash;3 months per episode and 34% for \u0026ge;\u0026thinsp;12 months of cumulative breastfeeding(\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e).For infants, evidence suggests that breastfeeding protects against infections, reduces the incidence of childhood obesity and diabetes, and may modestly enhance cognitive development.\u003c/p\u003e \u003cp\u003eHowever, at present, the diagnosis of LM still relies on clinical symptoms and signs, non-specific laboratory tests. For example, when infection occurs, the affected breast develops a wedge-shaped erythematous area characterized by tenderness, localized heat, and swelling, accompanied by pyrexia and systemic manifestations (such as a temperature above 38.5\u0026deg;C, chills, flu-like aching)(\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e).Laboratory tests will typically reveal elevated white blood cell count, neutrophils, and C-reactive protein (CRP). In the absence of typical clinical manifestations and biomarker alterations, clinicians with limited experience may overlook or misdiagnose the condition. By the time these characteristic signs and laboratory abnormalities appear, the disease has often progressed to an advanced stage. Therefore, early-stage quantitative diagnostic methods with high specificity are critical. Accurate identification of LM enables timely clinical intervention, thereby improving prognosis. Therefore, it is particularly important to search for specific quantitative indicators related to LM.\u003c/p\u003e \u003cp\u003eAs early as the 1960s, Smith et al(\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e). first documented alterations in milk electrolyte concentrations and electrical conductivity (EC) during bovine LM. By the 1990s, milk EC measurement had been adopted as an experimental screening indicator for mastitis(\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e). Subsequent animal studies in dairy cows and goats consistently demonstrated increased concentrations of specific ions (notably Na⁺ and Cl⁻) in milk during LM episodes(\u003cspan additionalcitationids=\"CR13\" citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e).LM is fundamentally an inflammatory response of mammary tissue(\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e). During inflammation, cytokines damage local capillaries and parenchyma, disrupting tight junctions between epithelial cells and increasing vascular/alveolar permeability(\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e). By this same pathological mechanism, when LM occurs in humans, Na⁺ and Cl⁻ (abundant in extracellular fluid) diffuse into the alveolar lumen through compromised tight junctions. To maintain osmotic equilibrium, K⁺ concentrations consequently decrease(\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e).While milk electrolyte concentration and EC measurements have been widely adopted for detecting LM in veterinary medicine, their efficacy in human clinical practice remains unverified due to a lack of robust studies.\u003c/p\u003e \u003cp\u003eThis study investigates milk electrolyte concentrations (Na⁺, K⁺, Cl⁻, Ca\u0026sup2;⁺) and EC in healthy lactating women and examines their changes during LM, with the objectives of establishing diagnostic cutoff values to differentiate healthy and LM-affected individuals. The findings will facilitate future research on pathogen-specific correlations, disease progression patterns, and potential clinical applications for early antibiotic guidance in LM.\u003c/p\u003e"},{"header":"METHODS","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eStudy subjects\u003c/h2\u003e \u003cp\u003eAll enrolled LM patients were treated at the Department of Breast Surgery, Chengdu Women\u0026rsquo;s and Children\u0026rsquo;s Central Hospital, and Pengzhou Maternal and Child Health Hospital between January 2024 and March 2025 (including 91 cases from Chengdu Women\u0026rsquo;s and Children\u0026rsquo;s Hospital and 30 cases from Pengzhou Maternal and Child Health Hospital).Our healthy control group consisted of lactating women without breast diseases who visited the same hospitals during the same period (including 89 cases from Chengdu Women\u0026rsquo;s and Children\u0026rsquo;s Hospital and 30 cases from Pengzhou Maternal and Child Health Hospital).\u003c/p\u003e \u003cp\u003eInclusion Criteria:1) Aged 18\u0026ndash;40 years, 2) Exclusively breastfeeding, 3) Parity\u0026thinsp;\u0026le;\u0026thinsp;2, 4) No history of breast diseases (including LM, breast tumors, or trauma), 5) No prior breast surgery (including minimally invasive procedures) or chest wall radiotherapy, 6) No antibiotic use during lactation. Exclusion Criteria: 1) Age\u0026thinsp;\u0026lt;\u0026thinsp;18 or \u0026gt;\u0026thinsp;40 years, 2) Non-exclusive breastfeeding, 3) Parity\u0026thinsp;\u0026gt;\u0026thinsp;2, 4) History of LM, breast neoplasms, or trauma, 5) Prior breast surgery/radiotherapy, 6) Postpartum antibiotic use, 7) Severe cognitive impairment (unable to provide informed consent), 8) Auditory dysfunction affecting compliance.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eMilk sample collection and Laboratory analysis\u003c/h3\u003e\n\u003cp\u003e \u003cb\u003eSample Collection\u003c/b\u003e: 1) pre-collection assessments: Record the age, parity, mode of delivery, and affected breast side (for mastitis group) for all participants,2)timing: a. healthy controls: milk samples collected between 9:00\u0026ndash;11:00 AM, excluding the first postpartum week, b. acute mastitis cases: Samples obtained prior to antibiotic administration, 3) sterile protocol: a. disinfected nipple/areolar area (5 cm radius) with iodophor swabs (3\u0026ndash;4 wipes), b. discarded initial droplets, c. collected 15 mL per breast using hospital-grade electric pumps, labeled accordingly.\u003c/p\u003e \u003cp\u003e \u003cb\u003eElectrolyte/Conductivity Measurement (A-tube samples)\u003c/b\u003e:1) environment: 23\u0026deg;C, 55% humidity, 2) Sample preparation: a. low-speed centrifugation: 4,000 rpm \u0026times; 30 min (4\u0026deg;C), b. collected supernatant \u0026rarr; High-speed centrifugation: 13,000 rpm \u0026times; 15 min (4\u0026deg;C), c. aspirated clear upper layer (minimizing lipid contamination).\u003c/p\u003e \u003cp\u003e \u003cb\u003eAnalysis\u003c/b\u003e:1) electrolytes (Na⁺, K⁺, Cl⁻, Ca\u0026sup2;⁺): Measured via auto-calibrated biochemical analyzer, 2) Conductivity: Quantified using calibrated urine analyzer with dedicated cups. The Apparatus and Chemicals used in the experimental procedures are listed in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eApparatus and Chemicals Used\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eName\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eManufacturer\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCat.No.\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAutomatic Biochemical Analyzer\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eHitachi Diagnostic Products Co., Ltd.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eLabospect-008-AS\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAutomatic Urine Analyzer\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eDajia Medical Testing Co., Ltd.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eUC-3500\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHitachi ISE Reference Electrode Solution\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eHitachi Instruments Co., Ltd.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eHitachi ISE Standard Solution (Su 0009-2007)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003eStatistical analysis\u003c/h2\u003e \u003cp\u003e1)Excluded objectively unreliable or incomplete records per NCCLS-C28-A2 and Chinese WS/T 402\u0026ndash;2012 standards for reference interval establishment, 2) Analytical Methods (SPSS 25.0): descriptive statistics: a. normally distributed data: mean\u0026thinsp;\u0026plusmn;\u0026thinsp;SD (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\stackrel{-}{x}\\)\u003c/span\u003e\u003c/span\u003e \u0026plusmn; s), b. non-normal data: median (P25, P75), c. categorical data: n (%). Inferential statistics: a. normally distributed variables: Independent t-test, b. non-normal variables: Mann-Whitney U test, c. Parity (healthy vs. mastitis groups): χ\u0026sup2; test (R\u0026times;C contingency table),3. Optimal cutoff values (Na⁺, K⁺, Cl⁻, Ca\u0026sup2;⁺, EC): ROC-derived, validated by χ\u0026sup2; test, 4) Significance threshold: Two-tailed \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05.\u003c/p\u003e \u003c/div\u003e"},{"header":"RESULTS","content":"\u003cp\u003e \u003cb\u003e1.General Characteristics\u003c/b\u003e \u003c/p\u003e \u003cp\u003eThis study included 119 healthy lactating women (119 cases) and 121 patients with LM (121 cases). The healthy group had a mean age of 28.53\u0026thinsp;\u0026plusmn;\u0026thinsp;3.67 years (range: 22\u0026ndash;38), while the mastitis group averaged 29.30\u0026thinsp;\u0026plusmn;\u0026thinsp;3.29 years (range: 22\u0026ndash;38). Both groups had parity ranging from 1 to 2 deliveries, with 103 cases (86.55%) being primiparous and 16 cases (13.45%) multiparous in the healthy group, compared to 107 primiparous (88.43%) and 14 multiparous (11.57%) cases in the mastitis group. Regarding delivery mode, the healthy group included 87 vaginal deliveries (73.11%) and 32 cesarean sections (26.89%), whereas the mastitis group had 92 vaginal deliveries (76.03%) and 29 cesarean sections (23.97%). In the mastitis group, the affected breast was left-sided in 69 cases (57.02%) and right-sided in 52 cases (42.98%) (Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e2\u003c/span\u003e\u0026thinsp;\u0026minus;\u0026thinsp;1).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2.1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eGeneral Characteristics\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"3\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003e\u003cb\u003eAge in year\u003c/b\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMastitis group(n\u0026thinsp;=\u0026thinsp;121)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eHealthy group(n\u0026thinsp;=\u0026thinsp;119)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003e29.30(22,38)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003e28.53(22,38)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eParity\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e1(107, 88.43%)\u003c/p\u003e \u003cp\u003e2(14,11.57%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1(103,86.55%)\u003c/p\u003e \u003cp\u003e2(16, 13.45%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eDelivery mode\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eVaginal delivery:\u003c/p\u003e \u003cp\u003e(92, 76.03%)\u003c/p\u003e \u003cp\u003eCesarean section:\u003c/p\u003e \u003cp\u003e(29, 23.97%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eVaginal delivery:\u003c/p\u003e \u003cp\u003e(87, 73.11%)\u003c/p\u003e \u003cp\u003eCesarean section:\u003c/p\u003e \u003cp\u003e(32, 26.89%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eBreast laterality in mastitis cases\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eLeft:69(57.02%)\u003c/p\u003e \u003cp\u003eRight:52(42.98%)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eNo significant differences were observed between groups regarding age, parity, or delivery mode (all \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.05, Table\u0026nbsp;\u0026lt;link rid=\"tb3\"\u0026gt;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e2\u0026lt;/link\u0026gt;\u003c/span\u003e\u0026ndash;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e2\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003e2 Comparison of Baseline Characteristics\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGroup\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eAge in year\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eParity\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eDelivery mode\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eBreast laterality in mastitis cases\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eHealthy group\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e28.53\u0026thinsp;\u0026plusmn;\u0026thinsp;3.67\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1(86.55%)\u003c/p\u003e \u003cp\u003e2(13.45%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eVaginal delivery: 87(73.11%)\u003c/p\u003e \u003cp\u003eCesarean section: 32(26.89%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eMastitis group\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e29.30\u0026thinsp;\u0026plusmn;\u0026thinsp;3.29\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1(88.43%)\u003c/p\u003e \u003cp\u003e2(11.57%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eVaginal delivery: 92(76.03%)\u003c/p\u003e \u003cp\u003eCesarean section: 29(23.97%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eLeft:57.02%\u003c/p\u003e \u003cp\u003eRight:42.98%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003ep\u003c/b\u003e\u003cb\u003e-Value\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.089\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.662\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.603\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003e2.Comparison of Electrolyte Concentrations and EC Between Bilateral Breasts in Healthy Lactating Women\u003c/b\u003e \u003c/p\u003e \u003cp\u003eThe Shapiro-Wilk test for normality showed that the concentrations of Na\u003csup\u003e+\u003c/sup\u003e, K\u003csup\u003e+\u003c/sup\u003e, Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e, Ca\u003csup\u003e2+\u003c/sup\u003e, and EC in the breast milk of the healthy group did not follow a normal distribution (\u003cem\u003ep\u003c/em\u003e\u0026lt;0.05). Therefore, the Mann-Whitney U test (a nonparametric test for two independent samples) was used to compare the experimental data of bilateral breast milk Na\u003csup\u003e+\u003c/sup\u003e, K\u003csup\u003e+\u003c/sup\u003e, Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e, Ca\u003csup\u003e2+\u003c/sup\u003econcentrations, as well as EC in the healthy group. In the healthy group, the left breast milk Na\u003csup\u003e+\u003c/sup\u003e, K\u003csup\u003e+\u003c/sup\u003e, Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e, Ca\u003csup\u003e2+\u003c/sup\u003econcentrations, and EC were11.70 (9.90, 13.40) mmol/L, 13.50 (11.80, 16.05) mmol/L, 13.80 (12.00, 15.30) mmol/L, 5.56 (4.90, 6.18) mmol/L, and 1.40 (1.00, 1.90) \u0026micro;S/cm, respectively. The right breast milk Na\u003csup\u003e+\u003c/sup\u003e, K\u003csup\u003e+\u003c/sup\u003e, Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e, Ca\u003csup\u003e2+\u003c/sup\u003e concentrations, and EC were 11.10 (9.10, 12.50) mmol/L, 14.30 (11.94, 14.91) mmol/L, 13.40 (11.80, 15.30) mmol/L, 5.53 (4.89, 6.10) mmol/L, and 1.3 (0.80, 1.70) \u0026micro;S/cm, respectively. No statistically significant differences were observed between the left and right breast milk Na\u003csup\u003e+\u003c/sup\u003e, K\u003csup\u003e+\u003c/sup\u003e, Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e, Ca\u003csup\u003e2+\u003c/sup\u003e concentrations, or EC in the healthy group (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.05) (see Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eComparison of bilateral breast milk electrolyte concentrations and electrical conductivity in the healthy group\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGroup\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNa\u003csup\u003e+\u003c/sup\u003e(mmol/L)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eK\u003csup\u003e+\u003c/sup\u003e(mmol/L)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eCl\u003csup\u003e-\u003c/sup\u003e(mmol/L)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCa\u003csup\u003e2+\u003c/sup\u003e(mmol/L)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eEC(\u0026micro;S/cm)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eLeft\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e11.70\u003c/p\u003e \u003cp\u003e(9.90, 13.40)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e13.50 (11.80,16.05)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e13.80\u003c/p\u003e \u003cp\u003e(12.00, 15.30)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e5.56 (4.90,6.18)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1.4 (1.0,1.90)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eRight\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e11.10\u003c/p\u003e \u003cp\u003e(9.10, 12.50)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e14.3 (11.94,14.91)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e13.40\u003c/p\u003e \u003cp\u003e(11.80, 15.30)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e5.53 (4.89,6.10)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1.3 (0.80,1.70)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eZ-score\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-2.645\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e-1.292\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-1.786\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e-1.134\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e-0.214\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003ep\u003c/b\u003e\u003cb\u003e-Value\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.08\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e0.196\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.074\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e0.257\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e0.813\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003e3.Comparison of Electrolyte Concentrations and EC Between Affected and Unaffected Breasts in LM Patients\u003c/b\u003e \u003c/p\u003e \u003cp\u003eThis study analyzed 121 cases of LM, comparing electrolyte concentrations and EC between affected and unaffected breasts. The Shapiro-Wilk test confirmed non-normal distribution for all parameters (Na\u003csup\u003e+\u003c/sup\u003e, K\u003csup\u003e+\u003c/sup\u003e, Cl\u003csup\u003e-\u003c/sup\u003e, Ca\u003csup\u003e2+\u003c/sup\u003e concentrations and EC; \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05), necessitating use of the Wilcoxon signed-rank test.\u003c/p\u003e \u003cp\u003eSignificant differences were observed between affected and unaffected breasts. Affected breasts showed elevated Na\u003csup\u003e+\u003c/sup\u003e (12.50 [7.90\u0026ndash;16.1] vs 7.80 [7.20-13.25] mmol/L), K\u003csup\u003e+\u003c/sup\u003e (17.82 [14.3\u0026ndash;18.80] vs 13.34 [10.58\u0026ndash;15.49] mmol/L), Cl\u003csup\u003e-\u003c/sup\u003e (13.30 [11.60\u0026ndash;17.80] vs 11.60 [8.90\u0026ndash;14.10] mmol/L), Ca\u003csup\u003e2+\u003c/sup\u003e (5.80 [5.42\u0026ndash;6.47] vs 5.57 [4.88\u0026ndash;6.36] mmol/L), and EC (1.90 [1.40\u0026ndash;2.40] vs 1.20 [0.90\u0026ndash;1.40] \u0026micro;S/cm). All differences were statistically significant (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05), demonstrating consistent elevation of these parameters in affected breasts compared to unaffected controls (Table\u0026nbsp;\u003cspan refid=\"Tab5\" class=\"InternalRef\"\u003e4\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab5\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eComparison of Electrolyte Concentrations and EC Between Affected and Unaffected Breasts in LM Patients\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGroup\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNa\u003csup\u003e+\u003c/sup\u003e(mmol/L)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eK\u003csup\u003e+\u003c/sup\u003e(mmol/L)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eCl\u003csup\u003e-\u003c/sup\u003e(mmol/L)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCa\u003csup\u003e2+\u003c/sup\u003e(mmol/L)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eEC(\u0026micro;S/cm)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eAffected Side\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e12.50\u003c/p\u003e \u003cp\u003e(7.90,16.1)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e17.82\u003c/p\u003e \u003cp\u003e(14.3,18.80)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e13.30\u003c/p\u003e \u003cp\u003e(11.60,17.80)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e5.80\u003c/p\u003e \u003cp\u003e(5.42,6.47)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1.90\u003c/p\u003e \u003cp\u003e(1.40,2.40)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eUnaffected Side\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e7.80\u003c/p\u003e \u003cp\u003e(7.20,13.25)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e13.34\u003c/p\u003e \u003cp\u003e(10.58,15.49)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e11.60\u003c/p\u003e \u003cp\u003e(8.90,14.10)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e5.57\u003c/p\u003e \u003cp\u003e(4.88,6.36)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1.20\u003c/p\u003e \u003cp\u003e(0.90,1.40)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eZ-Score\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e-4.683\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e-7.700\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e-4.429\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e-2.904\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e-7.276\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003ep\u003c/b\u003e\u003cb\u003e-Value\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u0026lt;0.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e\u0026lt;0.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e\u0026lt;0.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u0026lt;0.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e\u0026lt;0.05\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003e4.Comparison of electrolyte concentrations and EC in breast milk between healthy and mastitis-affected groups\u003c/b\u003e \u003c/p\u003e \u003cp\u003eAs the breast milk electrolyte concentrations and EC data from both healthy and mastitis groups showed non-normal distribution (Shapiro-Wilk test, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05), the Mann-Whitney U test was used for statistical analysis. For the healthy group, the average values of bilateral breast milk measurements were used for comparison with the affected side of mastitis patients. The mastitis group comprised 121 patients (121 samples).\u003c/p\u003e \u003cp\u003eThe healthy group showed the following median (IQR) values: Na\u003csup\u003e+\u003c/sup\u003e concentration 11.00 (9.30,13.10) mmol/L, K\u003csup\u003e+\u003c/sup\u003e concentration 13.56 (11.87,15.66) mmol/L, Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e concentration 11.98 (11.15,13.99) mmol/L, Ca\u003csup\u003e2+\u003c/sup\u003e concentration 5.44 (4.97,6.02) mmol/L, and EC1.35 (1.0,1.70) \u0026micro;S/cm. In comparison, the mastitis-affected side demonstrated: Na\u003csup\u003e+\u003c/sup\u003e 12.50 (7.90,16.10) mmol/L, K\u003csup\u003e+\u003c/sup\u003e 17.82 (14.30,18.80) mmol/L, Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e13.30 (11.60,17.8) mmol/L, Ca\u003csup\u003e2+\u003c/sup\u003e 5.80 (5.42,6.47) mmol/L, and EC 1.90 (1.40,2.40) \u0026micro;S/cm.\u003c/p\u003e \u003cp\u003eComparison of breast milk Na\u003csup\u003e+\u003c/sup\u003e, K\u003csup\u003e+\u003c/sup\u003e, Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e, and Ca\u003csup\u003e2+\u003c/sup\u003e concentrations and EC between the healthy group and affected side of the mastitis group showed statistically significant differences in all measured parameters (\u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05), with higher values observed in the mastitis group compared to the healthy group (Table\u0026nbsp;\u003cspan refid=\"Tab6\" class=\"InternalRef\"\u003e5\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab6\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 5\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eComparison of electrolyte concentrations and EC between healthy group and affected side of LM\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eGroup\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNa\u003csup\u003e+\u003c/sup\u003e(mmol/L)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eK\u003csup\u003e+\u003c/sup\u003e(mmol/L)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eCl\u003csup\u003e-\u003c/sup\u003e(mmol/L)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eCa\u003csup\u003e2+\u003c/sup\u003e(mmol/L)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eEC(\u0026micro;S/cm)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eHealthy Group\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e11.00 (9.30,13.10)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e13.56 (11.87,15.66)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e11.98 (11.15,13.99)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e5.44 (4.97,6.02)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1.35 (1.0,1.70)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eMastitis Group\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e12.50 (7.90,16.10)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e17.82 (14.30,18.80)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e13.30 (11.60,17.8)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e5.80 (5.42,6.47)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e1.90 (1.40,2.40)\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eZ-Score\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e-2.890\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e-7.574\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e-4.500\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e-5.696\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e-3.581\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003ep\u003c/b\u003e\u003cb\u003e-Value\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e\u0026lt;0.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e\u0026lt;0.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e\u0026lt;0.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e\u0026lt;0.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e\u0026lt;0.05\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003e5 Diagnostic Thresholds for LM: Electrolyte Concentrations and EC Optimal Cut-off Values\u003c/b\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003e5.1 ROC Curve Analysis for Milk Electrolyte Concentrations and EC in Lactational Mastitis\u003c/b\u003e \u003c/p\u003e \u003cp\u003eThe Na\u003csup\u003e+\u003c/sup\u003e, K\u003csup\u003e+\u003c/sup\u003e, Cl\u003csup\u003e-\u003c/sup\u003e, and Ca\u003csup\u003e2+\u003c/sup\u003e concentrations and EC in breast milk from the affected side of LM patients showed statistically significant differences compared to healthy controls. Using the \u003cem\u003eDiagnosis and Treatment Guidelines for Lactational Mastitis in China\u003c/em\u003e as the diagnostic standard, we constructed ROC curves for all parameter (Figs.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). The analysis revealed significant diagnostic performance for all measures: Na\u003csup\u003e+\u003c/sup\u003e concentration showed an AUC of 0.608 (95% CI: 0.533\u0026ndash;0.683, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05), K\u003csup\u003e+\u003c/sup\u003e concentration 0.783 (95% CI: 0.724\u0026ndash;0.842, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05), Cl\u003csup\u003e-\u003c/sup\u003e concentration 0.634 (95% CI: 0.561\u0026ndash;0.707, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05), Ca\u003csup\u003e2+\u003c/sup\u003e concentration 0.668 (95% CI: 0.600-0.736, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05), and EC 0.713 (95% CI: 0.648\u0026ndash;0.777, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eReceiver operating characteristic (ROC) curves illustrating the sensitivity and specificity of sodium ions (Na⁺), potassium ions (K⁺), chloride ions (Cl⁻), calcium ions (Ca\u0026sup2;⁺), and electrical conductivity (EC) in differentiating between affected and unaffected breasts. The diagonal reference line (dashed) represents no discriminatory ability (AUC\u0026thinsp;=\u0026thinsp;0.5). AUC, area under the curve.\u003c/p\u003e \u003cp\u003e \u003cb\u003e5.1 Calculate the Optimal Cutoff Values for Na⁺, K⁺, Cl⁻, and Ca\u0026sup2;⁺, as well as EC\u003c/b\u003e \u003c/p\u003e \u003cp\u003eThe Youden index (sensitivity+specificity-1) was calculated to determine optimal cutoff values for Na⁺ concentration, K⁺ concentration, Cl⁻ concentration, Ca\u0026sup2;⁺ concentration, and EC. The maximum Youden indices were 0.329, 0.536, 0.387, 0.328, and 0.391 for Na⁺ concentration, K⁺ concentration, Cl⁻ concentration, Ca\u0026sup2;⁺ concentration, and EC, respectively. The corresponding optimal cutoff values were 14.300 mmol/L for Na⁺ concentration, 16.985 mmol/L for K⁺ concentration, 14.688 mmol/L for Cl⁻ concentration, 6.055 mmol/L for Ca\u0026sup2;⁺ concentration, and 1.475 \u0026micro;S/cm for EC.\u003c/p\u003e \u003cp\u003e \u003cb\u003e5.2 The Optimal Cutoff Values for Na⁺ concentration, Cl⁻ concentration, and EC were Further Validated Using Chi-square (χ\u0026sup2;) tests.\u003c/b\u003e \u003c/p\u003e \u003cp\u003eUsing cutoff values of 14.300 mmol/L for Na⁺ concentration, 16.985 mmol/L for K⁺ concentration, 14.688 mmol/L for Cl⁻ concentration, 6.055 mmol/L for Ca\u0026sup2;⁺ concentration, and 1.475 \u0026micro;S/cm for EC, patients were stratified into healthy and mastitis groups. Chi-square tests revealed statistically significant differences between groups for all cutoff parameters (Na⁺: χ\u0026sup2;=32.527, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05; K⁺: χ\u0026sup2;=80.377, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05; Cl⁻: χ\u0026sup2;=10.660, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05; Ca\u0026sup2;⁺: χ\u0026sup2;=29.010, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05; conductivity: χ\u0026sup2;=37.033, \u003cem\u003ep\u003c/em\u003e\u0026thinsp;\u0026lt;\u0026thinsp;0.05) (Table\u0026nbsp;\u003cspan refid=\"Tab7\" class=\"InternalRef\"\u003e6\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab7\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 6\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eDiagnostic Thresholds for Lactational Mastitis: Electrolyte Concentrations and Conductivity Optimal Cut-off Values\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eParameter\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCut-off Value\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eAUC\u003c/p\u003e \u003cp\u003e(95% CI)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eSensitivity\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eSpecificity\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eχ\u0026sup2;-Score\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003e\u003cem\u003ep\u003c/em\u003e-value\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eNa\u003c/b\u003e\u003csup\u003e\u003cb\u003e+\u003c/b\u003e\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e14.300\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.608\u003c/p\u003e \u003cp\u003e(0.533\u0026ndash;0.683)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e43.80%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e89.10%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e32.527\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.05\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eK\u003c/b\u003e\u003csup\u003e\u003cb\u003e+\u003c/b\u003e\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e16.985\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.783\u003c/p\u003e \u003cp\u003e(0.724\u0026ndash;0.842)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e57.90%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e95.80%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e80.377\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.05\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eCl\u003c/b\u003e\u003csup\u003e\u003cb\u003e-\u003c/b\u003e\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e14.688\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.634\u003c/p\u003e \u003cp\u003e(0.561\u0026ndash;0.707)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e45.50%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e93.30%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e10.660\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.05\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eCa\u003c/b\u003e\u003csup\u003e\u003cb\u003e2+\u003c/b\u003e\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e6.055\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.668\u003c/p\u003e \u003cp\u003e(0.600-0.736)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e49.60%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e83.20%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e29.010\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.05\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e\u003cb\u003eEC\u003c/b\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c2\"\u003e \u003cp\u003e1.475\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.713\u003c/p\u003e \u003cp\u003e(0.648\u0026ndash;0.777)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e74.40%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e64.70%\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e37.033\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e\u0026lt;\u0026thinsp;0.05\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e"},{"header":"DISCUSSION","content":"\u003cp\u003eLM negatively impacts maternal and infant health, but its diagnosis remains reliant on nonspecific clinical signs and symptoms. Recent pathological findings underscore the need for objective biomarkers. This study analyzes electrolyte concentrations and EC in processed breast milk samples to investigate their correlation with LM, aiming to establish a theoretical basis for more specific diagnostic methods.\u003c/p\u003e \u003cp\u003e \u003cb\u003eMechanisms underlying altered Na\u003c/b\u003e \u003csup\u003e \u003cb\u003e+\u003c/b\u003e \u003c/sup\u003e, \u003cb\u003eCl\u003c/b\u003e\u003csup\u003e\u003cb\u003e\u0026minus;\u003c/b\u003e\u003c/sup\u003e \u003cb\u003elevels and EC in inflamed breast milk.\u003c/b\u003e\u003c/p\u003e \u003cp\u003eThe differences in Na\u003csup\u003e+\u003c/sup\u003e, Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e concentrations and EC between affected/unaffected breasts in LM patients, and between healthy lactating women and LM patients, may be closely associated with LM pathogenesis.\u003c/p\u003e \u003cp\u003eTwo distinct hypotheses exist regarding the pathogenesis of LM. The infectious theory posits that it is primarily a microbial disease, supported by cultured pathogens such as Staphylococcus aureus, Escherichia coli, and Streptococcus spp. from milk samples using advanced bacteriological techniques(\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e).Staphylococcus epidermidis, a commensal bacterium colonizing human skin and mucous membranes, has recently been identified in milk samples from LM cases, suggesting its potential role as an emerging pathogen in this condition(\u003cspan additionalcitationids=\"CR20\" citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e).These findings historically supported the classification of LM as an infectious disease. However, emerging research has led some scholars to challenge this simplistic etiological framework(\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e).This leads to an alternative hypothesis, proposing LM as primarily an inflammatory disorder. Regardless of whether LM is classified as an infectious or inflammatory disease, its molecular mechanisms are closely linked to Toll-like receptor (TLR) signaling pathways\u0026mdash;either triggered by microbe-associated molecular patterns (MAMPs) or damage-associated molecular patterns (DAMPs).\u003c/p\u003e \u003cp\u003eThe pathogenesis of infectious LM may involve the MAMP-mediated TLR signaling pathway. Among the pattern recognition receptors (PRRs), TLR2, TLR4 and TLR5 specifically recognize bacterial components such as lipoteichoic acid, lipopolysaccharide, flagellin and bacterial lipopeptides. Upon binding to these MAMPs, TLRs transduce extracellular signals into the cell, leading to activation of the transcription factor NF-κB. This subsequently triggers transcriptional and translational processes that result in the release of various inflammatory cytokines, chemokines and adhesion molecules, while simultaneously recruiting other innate immune components such as neutrophils to the site of infection(\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn the absence of pathogenic bacteria, host-derived DAMPs can activate TLRs through sterile inflammatory pathways(\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e). DAMPs promote inflammatory responses via two distinct mechanisms: 1) Direct activation of inflammatory mediators that subsequently trigger TLRs and downstream NF-κB signaling(\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e), and 2) Potentiation of TLR-mediated immune responses in sterile environments through positive feedback amplification of TLR/NF-κB activation, ultimately contributing to the development of inflammatory lactational mastitis(\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe inflammatory cytokines induced through two distinct signaling pathways trigger pathological changes in mammary tissue, including damage to capillary walls and glandular acini, thereby increasing epithelial permeability(\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e). This leads to altered milk composition. During inflammatory conditions, cytokines disrupt tight junctions between acinar cells and enhance capillary permeability, allowing elevated Na\u003csup\u003e+\u003c/sup\u003e and Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e from extracellular fluid to enter the mammary gland acinar cavity. Consequently, during LM, concentrations of certain ions (e.g., Na\u003csup\u003e+\u003c/sup\u003e and Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e) increase in breast milk\u0026mdash;a finding consistent with prior animal studies and our results(\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e).Milk conductivity is primarily determined by its ionic composition (Na\u003csup\u003e+\u003c/sup\u003e, K\u003csup\u003e+\u003c/sup\u003e, Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e), as centrifugation excludes interference from organic components (e.g., fat, proteins). Thus, the LM-induced elevation in Na\u003csup\u003e+\u003c/sup\u003e and Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e concentrations directly contributes to increased EC. Another school of thought suggests that under inflammatory conditions, the decreased lactose content in milk triggers a compensatory increase in Na\u003csup\u003e+\u003c/sup\u003e and Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e concentrations to maintain osmotic equilibrium with plasma, a finding consistent with our results.\u003c/p\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eMechanisms Underlying Altered K\u003csup\u003e+\u003c/sup\u003e Concentrations in LM Milk Compared to Healthy Controls\u003c/h2\u003e \u003cp\u003eWegner et al. (\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e)investigated 56 Holstein cows to evaluate mastitis using milk electrolyte concentrations and EC as diagnostic indicators. Their findings revealed that LM milk exhibited significantly elevated Na\u003csup\u003e+\u003c/sup\u003e and Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e concentrations along with decreased K\u003csup\u003e+\u003c/sup\u003e levels compared to healthy controls, accompanied by altered EC values. Our data demonstrate elevated milk K⁺ levels in mastitis-affected breasts compared to healthy controls (healthy: 13.56 (11.87,15.66) mmol/L vs. inflammatory: 17.82 (14.30,18.80) mmol/L), contrasting with bovine studies typically reporting decreased K⁺ during mastitis. This adverse finding may be attributed to two potential mechanisms: 1) necrosis of mammary alveolar epithelial cells releasing intracellular K\u003csup\u003e+\u003c/sup\u003e into the mammary gland acinar cavity, thereby counteracting the LM-induced K\u003csup\u003e+\u003c/sup\u003e reduction; and 2) inflammatory cytokine-mediated impairment of Na\u003csup\u003e+\u003c/sup\u003e/K\u003csup\u003e+\u003c/sup\u003e-ATPase pump efficiency, reducing K\u003csup\u003e+\u003c/sup\u003e influx. However, the exact underlying mechanisms require further investigation.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eMechanisms Underlying Altered Ca Concentrations in LM Milk Compared to Healthy Controls\u003c/h3\u003e\n\u003cp\u003eDalal et al.(\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e) demonstrated that Ca\u0026sup2;⁺ signaling in endothelial cells serves as a critical regulatory mechanism for inflammatory responses. Their work revealed that inflammation-mediated Ca\u0026sup2;⁺ influx leads to decreased serum Ca\u0026sup2;⁺ concentrations, suggesting systemic Ca\u0026sup2;⁺ redistribution during immune activation. Previous animal studies have suggested that decreased milk Ca\u0026sup2;⁺concentrations reflect inflammatory status, a finding inconsistent with our results. This discrepancy may be attributed to dual mechanisms in LM: 1) inflammation-induced extracellular Ca\u003csup\u003e2+\u003c/sup\u003e influx, coupled with 2) cytokine-mediated increases in capillary and mammary alveolar permeability, which collectively facilitate diffusion of high-concentration extracellular Ca\u003csup\u003e2+\u003c/sup\u003e into the mammary acini. These compensatory processes may maintain or elevate Ca\u003csup\u003e2+\u003c/sup\u003e concentrations in milk despite the inflammatory milieu. Additionally, macromolecular components in milk may influence ionic calcium levels. For instance, casein - whose production decreases during inflammatory states due to impaired mammary synthetic capacity - normally binds ionic calcium. The reduction in casein content could consequently lead to increased free ionic Ca\u003csup\u003e2+\u003c/sup\u003econcentrations in milk. Methodological differences may further explain the discrepancy with prior animal studies. While previous research employed real-time electrolyte measurements, our protocol required sample preprocessing, suggesting that variations in measurement standards may affect result comparability. Furthermore, species-specific differences in Ca\u003csup\u003e2+\u003c/sup\u003e homeostasis may exist between humans and dairy cows during LM. The underlying regulatory mechanisms remain to be elucidated through further investigation.\u003c/p\u003e\n\u003ch3\u003eDiagnostic Thresholds of Na⁺, K⁺, Cl⁻, Ca²⁺ Concentrations and EC in LM\u003c/h3\u003e\n\u003cp\u003eThis study preliminarily established optimal cutoff values for Na⁺ (14.300 mmol/L), K⁺ (16.985 mmol/L), Cl⁻ (14.688 mmol/L), and Ca\u0026sup2;⁺ (6.055 mmol/L) concentrations, along with EC (1.475 \u0026micro;S/cm) in breast milk, demonstrating significant discriminative ability between healthy lactating women and those with LM. The corresponding receiver operating characteristic curve analysis yielded area under the curve values of 0.608 (95% CI: 0.533\u0026ndash;0.683, P\u0026thinsp;\u0026lt;\u0026thinsp;0.05) for Na⁺, 0.783 (95% CI: 0.724\u0026ndash;0.842, P\u0026thinsp;\u0026lt;\u0026thinsp;0.05) for K⁺, 0.634 (95% CI: 0.561\u0026ndash;0.707, P\u0026thinsp;\u0026lt;\u0026thinsp;0.05) for Cl⁻, 0.668 (95% CI: 0.600-0.736, P\u0026thinsp;\u0026lt;\u0026thinsp;0.05) for Ca\u0026sup2;⁺, and 0.713 (95% CI: 0.648\u0026ndash;0.777, P\u0026thinsp;\u0026lt;\u0026thinsp;0.05) for EC, all showing statistically significant diagnostic performance. These findings provide important evidence for establishing noninvasive and objective diagnostic criteria in clinical practice for LM.\u003c/p\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003eLimitations and Future Directions\u003c/h2\u003e \u003cp\u003eThis study has several limitations that should be acknowledged. First and foremost, although the methods used to measure breast milk electrolytes and EC represent the gold standard for clinical serum electrolyte analysis and urinary EC measurement, they have not undergone comprehensive methodological validation for the complex matrix of human milk. The lack of systematic data on recovery rates, interference tests, and dilution linearity means that potential matrix effects on absolute accuracy cannot be ruled out. Second, due to equipment constraints and the absence of dedicated instruments for human milk, our instrumental setup, though chosen after expert consultation, may have inherent limitations for this specific application. Despite these limitations, we employed rigorous internal quality controls, standardized processing, and internal consistency checks (e.g., bilateral similarity in healthy participants) to bolster the reliability of our comparative findings. The significant differences observed between groups align with pathophysiology and support the method's discriminative capability. This study is an exploratory investigation in the field of human milk, building upon prior findings from mammalian research. Future studies should prioritize conducting matrix-specific validation before applying the methodology. Furthermore, developing or optimizing dedicated instruments for human milk analysis and conducting larger, multicenter cohort studies would be crucial for confirming and extending the findings of this research.\u003c/p\u003e \u003c/div\u003e"},{"header":"CONCLUSION","content":"\u003cp\u003ePathological alterations in LM lead to significant changes in milk electrolyte concentrations and EC. Diagnostic thresholds of Na\u003csup\u003e+\u003c/sup\u003e\u0026ge;14.300 mmol/L, K\u003csup\u003e+\u003c/sup\u003e \u0026ge;16.985 mmol/L, Cl\u003csup\u003e\u0026minus;\u003c/sup\u003e \u0026ge;14.688 mmol/L, Ca\u003csup\u003e2+\u003c/sup\u003e \u0026ge;6.055 mmol/L, or EC\u0026thinsp;\u0026ge;\u0026thinsp;1.475\u0026micro;S/cm indicate localized mammary inflammation. These objective quantitative criteria provide clinicians with an evidence-based alternative to empirical diagnosis, which may help reduce unnecessary antibiotic use during LM and ultimately improve breastfeeding continuation rates. Furthermore, our study provides conclusive evidence that milk production is significantly impaired in inflamed mammary glands. While our current study has elucidated the differential patterns of milk electrolyte concentrations and EC between healthy lactating women and those with LM, future research will focus on: 1) the correlation between these biochemical parameters and specific microbial etiologies of LM, 2) their dynamic changes across different stages of disease progression, and 3) exploring the long-term effects of LM on maternal and infant health. This systematic approach will establish a comprehensive evidence base regarding the pathophysiological relationships between milk physicochemical properties and LM pathogenesis.\u003c/p\u003e"},{"header":"Abbreviations","content":"\u003cdiv class=\"DefinitionList\"\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eLM\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eLactational mastitis\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eEC\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eElectrical conductivity\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eCRP\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eC-reactive protein\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eTLR\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eToll-like receptor\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eMAMPs\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eMicrobe-associated molecular patterns\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003eDAMPs\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003eDamage-associated molecular patterns\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv class=\"DefinitionListEntry\"\u003e \u003cdiv class=\"Term\"\u003ePRRs\u003c/div\u003e \u003cdiv class=\"Description\"\u003e \u003cp\u003ePattern recognition receptors\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eEthical approval\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis study was approved by The Institutional Review Board of Chengdu Women\u0026apos;s and Children\u0026apos;s Central Hospital (reference number2023[30]) and The Ethics Committee of Pengzhou Maternal and Child Health Hospital (reference number2023[001]). Informed consent was obtained from all participants prior to enrollment. And all authors could ensure the confidentiality of patient data. The study followed the latest version of the Helsinki Declaration.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConsent for publication\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of data and materials\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe datasets analysed during the current study are available from the corresponding author on reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that they have no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe funding for this study was provided by the Chengdu Municipal Health Commission, China, through the project titled \u0026quot;A Prospective Cohort Study on Diagnosing Early Lactation Mastitis Based on Breast Milk Electrolyte Concentrations and Electrical Conductivity\u0026quot; (Project No. 2023311).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors\u0026rsquo; contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eQ.H. and P.N. conceived and designed the study.\u0026nbsp;Q.H. and Y.M.T. wrote the first draft of the manuscript.\u0026nbsp;S.B.L, Y.M.T., Z.Y.L., Y.Y. ,Y,D.,Y.X.\u0026nbsp;performed sample collection, preparation and data gathering.\u0026nbsp;S.B.L., Q.H.,Z.Y.L. analyzed the data, interpreted the results.\u0026nbsp;All authors read and approved the final manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNot applicable.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eMorcomb EF, Dargel CM, Anderson SA, Mastitis. Rapid Evid Rev Am Fam Physician. 2024;110(2):174\u0026ndash;82.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLai BY, Yu BW, Chu AJ, Liang SB, Jia LY, Liu JP, et al. Risk factors for lactation mastitis in China: A systematic review and meta-analysis. PLoS ONE. 2021;16(5):e0251182.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCooney F, Petty-Saphon N. The Burden of Severe Lactational Mastitis in Ireland from 2006 to 2015. Ir Med J. 2019;112(1):855.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAmir LH. ABM clinical protocol #4: Mastitis, revised March 2014. Breastfeed Med. 2014;9(5):239\u0026ndash;43.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eO'Brien C, Quinn E, Murphy M, Lehane E, O'Leary DP, Livingstone V, et al. Breast abscess: Not just a puerperal problem. Breast J. 2020;26(2):339\u0026ndash;42.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAmir LH, Forster D, McLachlan H, Lumley J. Incidence of breast abscess in lactating women: report from an Australian cohort. BJOG. 2004;111(12):1378\u0026ndash;81.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhou Y, Chen J, Li Q, Huang W, Lan H, Jiang H. Association between breastfeeding and breast cancer risk: evidence from a meta-analysis. Breastfeed Med. 2015;10(3):175\u0026ndash;82.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMa X, Zhao LG, Sun JW, Yang Y, Zheng JL, Gao J, et al. Association between breastfeeding and risk of endometrial cancer: a meta-analysis of epidemiological studies. Eur J Cancer Prev. 2018;27(2):144\u0026ndash;51.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBabic A, Sasamoto N, Rosner BA, Tworoger SS, Jordan SJ, Risch HA, et al. Association Between Breastfeeding and Ovarian Cancer Risk. JAMA Oncol. 2020;6(6):e200421.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSmith A, Wheelock JV, Dodd FH. Effect of milking throughout pregnancy on milk yield in the succeeding lactation. J Dairy Sci. 1966;49(7):895\u0026ndash;6.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMusser JM, Anderson KL, Caballero M, Amaya D, Maroto-Puga J. Evaluation of a hand-held electrical conductivity meter for detection of subclinical mastitis in cattle. Am J Vet Res. 1998;59(9):1087\u0026ndash;91.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eProsser CG, Hartmann PE. Comparison of mammary gland function during the ovulatory menstrual cycle and acute breast inflammation in women. Aust J Exp Biol Med Sci. 1983;61(Pt 3):277\u0026ndash;86.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSemba RD. Mastitis and transmission of human immunodeficiency virus through breast milk. Ann N Y Acad Sci. 2000;918:156\u0026ndash;62.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eReviews of Physiology. Biochemistry and Pharmacology. Anticancer Res. 2016;36(9):4980.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eOmranipour R, Vasigh M, Mastitis. Breast Abscess, and Granulomatous Mastitis. Adv Exp Med Biol. 2020;1252:53\u0026ndash;61.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eFetherston CM, Lai CT, Hartmann PE. Relationships between symptoms and changes in breast physiology during lactation mastitis. Breastfeed Med. 2006;1(3):136\u0026ndash;45.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePrentice A, Prentice AM, Lamb WH. Mastitis in rural Gambian mothers and the protection of the breast by milk antimicrobial factors. Trans R Soc Trop Med Hyg. 1985;79(1):90\u0026ndash;5.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRimoldi SG, Pileri P, Mazzocco MI, Romeri F, Bestetti G, Calvagna N, et al. The Role of Staphylococcus aureus in Mastitis: A Multidisciplinary Working Group Experience. J Hum Lact. 2020;36(3):503\u0026ndash;9.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBerens P, Swaim L, Peterson B. Incidence of methicillin-resistant Staphylococcus aureus in postpartum breast abscesses. Breastfeed Med. 2010;5(3):113\u0026ndash;5.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRodvold KA, McConeghy KW. Methicillin-resistant Staphylococcus aureus therapy: past, present, and future. Clin Infect Dis. 2014;58(Suppl 1):S20\u0026ndash;7.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLasagno M, Ortiz M, Vissio C, Yaciuk R, Bonetto C, Pellegrino M, et al. Pathogenesis and inflammatory response in experimental caprine mastitis due to Staphylococcus chromogenes. Microb Pathog. 2018;116:146\u0026ndash;52.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKvist LJ, Larsson BW, Hall-Lord ML, Steen A, Schal\u0026eacute;n C. The role of bacteria in lactational mastitis and some considerations of the use of antibiotic treatment. Int Breastfeed J. 2008;3:6.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKawai T, Akira S. The role of pattern-recognition receptors in innate immunity: update on Toll-like receptors. Nat Immunol. 2010;11(5):373\u0026ndash;84.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMcDermott MF, Tschopp J. From inflammasomes to fevers, crystals and hypertension: how basic research explains inflammatory diseases. Trends Mol Med. 2007;13(9):381\u0026ndash;8.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBuchanan MM, Hutchinson M, Watkins LR, Yin H. Toll-like receptor 4 in CNS pathologies. J Neurochem. 2010;114(1):13\u0026ndash;27.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eEl Mezayen R, El Gazzar M, Seeds MC, McCall CE, Dreskin SC, Nicolls MR. Endogenous signals released from necrotic cells augment inflammatory responses to bacterial endotoxin. Immunol Lett. 2007;111(1):36\u0026ndash;44.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSamuvel DJ, Sundararaj KP, Nareika A, Lopes-Virella MF, Huang Y. Lactate boosts TLR4 signaling and NF-kappaB pathway-mediated gene transcription in macrophages via monocarboxylate transporters and MD-2 up-regulation. J Immunol. 2009;182(4):2476\u0026ndash;84.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSemba RD, Kumwenda N, Taha TE, Hoover DR, Lan Y, Eisinger W, et al. Mastitis and immunological factors in breast milk of lactating women in Malawi. Clin Diagn Lab Immunol. 1999;6(5):671\u0026ndash;4.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWegner TN, Stull JW. Relation between mastitis test score, mineral composition of milk, and blood electrolyte profiles in Holstein cows. J Dairy Sci. 1978;61(12):1755\u0026ndash;9.\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDalal PJ, Muller WA, Sullivan DP. Endothelial Cell Calcium Signaling during Barrier Function and Inflammation. Am J Pathol. 2020;190(3):535\u0026ndash;42.\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"bmc-pregnancy-and-childbirth","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"prch","sideBox":"Learn more about [BMC Pregnancy and Childbirth](http://bmcpregnancychildbirth.biomedcentral.com/)","snPcode":"","submissionUrl":"https://www.editorialmanager.com/prch/default.aspx","title":"BMC Pregnancy and Childbirth","twitterHandle":"@BMC_series","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"em","reportingPortfolio":"BMC Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Lactational mastitis, Milk electrolyte concentration and conductivity, quantitative diagnosis","lastPublishedDoi":"10.21203/rs.3.rs-9142757/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9142757/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003ch2\u003eBackground\u003c/h2\u003e \u003cp\u003eLactational mastitis (LM) is a common and painful postpartum condition. While studies in dairy animals have shown that milk electrolytes and electrical conductivity (EC) can indicate inflammation, human research is scarce. This study compares breast milk electrolyte levels and EC between healthy lactating women and those with LM to improve diagnostic accuracy for this condition.\u003c/p\u003e\u003ch2\u003eMethods\u003c/h2\u003e \u003cp\u003eWe collected bilateral breast milk from 119 lactating healthy women and 121 women with LM, recorded their clinical characteristics and explored the differences in milk electrolyte concentrations and EC. And then, the self-comparison of conductivity and EC in the inflammation group were recorded, the comparison of mean values in the infected group and the healthy group were conducted. Results indicated differences in electrolyte concentrations and EC between mastitis patients and healthy women. A preliminary optimal cut-off value was established and evaluated for its diagnostic utility in initial LM detection.\u003c/p\u003e\u003ch2\u003eResults\u003c/h2\u003e \u003cp\u003eThis study included 119 healthy postpartum women and 121 patients with LM. No significant differences in Na⁺, K⁺, Cl⁻, Ca\u0026sup2;⁺, or EC were found between left and right breasts in the healthy group. In the LM group, all parameters were significantly higher in affected versus unaffected breasts. All measures were also significantly elevated in the mastitis group compared to the healthy group. Based on these findings, preliminary diagnostic cutoff values were established: Na⁺ (14.300 mmol/L), K⁺ (16.985 mmol/L), Cl⁻ (14.688 mmol/L), Ca\u0026sup2;⁺ (6.055 mmol/L), and EC (1.475 mS/cm), offering objective criteria for clinical detection of LM.\u003c/p\u003e\u003ch2\u003eConclusions\u003c/h2\u003e \u003cp\u003eLM incidence is rising and remains a major reason for breastfeeding cessation. Current diagnosis relies on empirical assessment due to the absence of specific diagnostic criteria. Previous animal studies have linked mammary inflammation to alterations in breast milk Na⁺, K⁺, Cl⁻, and Ca\u0026sup2;⁺ levels and EC. Our study proposes preliminary cutoff values for these parameters to aid in accurate detection of mammary inflammation, potentially helping to improve breastfeeding continuation rates.\u003c/p\u003e","manuscriptTitle":"Electrolyte concentration and electrical conductivity of milk: ability to predict lactational mastitis status—A prospective cohort study","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-04-14 09:49:41","doi":"10.21203/rs.3.rs-9142757/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"editorInvitedReview","content":"","date":"2026-04-16T06:19:18+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"270767046743449801641764461739001243615","date":"2026-04-07T18:55:16+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-04-07T09:03:21+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2026-03-18T10:26:49+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-03-18T06:53:51+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-03-18T06:53:38+00:00","index":"","fulltext":""},{"type":"submitted","content":"BMC Pregnancy and Childbirth","date":"2026-03-17T01:38:04+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"bmc-pregnancy-and-childbirth","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"prch","sideBox":"Learn more about [BMC Pregnancy and Childbirth](http://bmcpregnancychildbirth.biomedcentral.com/)","snPcode":"","submissionUrl":"https://www.editorialmanager.com/prch/default.aspx","title":"BMC Pregnancy and Childbirth","twitterHandle":"@BMC_series","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"em","reportingPortfolio":"BMC Series","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"9535577f-806f-4ab1-886c-5fb5469af284","owner":[],"postedDate":"April 14th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-04-14T09:49:41+00:00","versionOfRecord":[],"versionCreatedAt":"2026-04-14 09:49:41","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9142757","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9142757","identity":"rs-9142757","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}