Impact of diabetes mellitus on stone access and surgical outcomes in patients undergoing ureteroscopic lithotripsy: a retrospective cohort study.

A total of 149 patients who underwent URS for ureteral calculi were divided into two groups: DM (Group 1, n  = 50) and non–DM (Group 2, n  = 99) (Table  1 ). A statistically significant difference was observed between the groups in age, height, BMI, and stone volume ( p  < 0.001, p  < 0.001, p  = 0.004, p  = 0.004, respectively). Stone volume demonstrated a right-skewed distribution with substantial variability, which is expected when stone burden is expressed in volumetric units. The mean maximum stone diameter did not differ significantly between the DM and non-DM groups (7.6 ± 3.1 mm vs. 8.2 ± 3.4 mm, p  = 0.271), suggesting that stone size was not a confounding factor influencing access difficulty. The rate of successful scope passage to the stone was significantly higher in Group 2 (85.9%) than in Group 1 (58.0%; p  < 0.001). The stone-free rate was also significantly higher in Group 2 ( p  = 0.033). There were no significant differences between groups 1 and 2 in gender, weight, operative time, hydronephrosis, stone side, stone localization, complications, and Clavien-Dindo classification (Table  1 ). Table 1 Comparison of demographic and clinical characteristics of the groups Characteristic DM ( n  = 50) Non-DM ( n  = 99) p -value Age 62.10 ± 11.56 43.05 ± 13.15 < 0.001 Gender 0.991 Woman 29 (58.0) 59 (59.6) Male 21 (42.0) 40 (40.4) Height (cm) 167.30 ± 7.16 172.29 ± 8.43 < 0.001 Weight (kg) 77.86 ± 10.42 77.86 ± 10.67 0.999 BMI (kg/m2) 27.88 ± 3.63 26.06 ± 3.19 0.004 Stone volume (mm³) 269.76 ± 421.05 367.27 ± 475.19 0.020 Duration of surgery 40.26 ± 23.60 33.77 ± 16.73 0.178 Successful scope passage to the stone < 0.001 Access failure 21 (42.0) 14 (14.1) Access success 29 (58.0) 85 (85.9) Hydronephrosis 0.487 No 10 (20.0) 14 (14.1) Grade 1–2 29 (58.0) 67 (67.7) Grade 3–4 11 (22.0) 18 (18.2) Side 0.353 Left 27 (54.0) 44 (44.4) Right 23 (46.0) 55 (55.6) Localization of the stone 0.834 Proximal ureter 20 (40.0) 36 (36.4) Middle ureter 11 (22.0) 26 (26.3) Distal ureter 19 (38.0) 37 (37.4) Stone-free 0.033 23 (46.0%) 65 (65.7%) Type of complication 0.982 PULS 0 46 (92.0) 89 (89.9) PULS 1 1 (2.0) 4 (4.0) PULS 2 1 (2.0) 1 (1.0) PULS 3 0 (0.0) 0 (0.0) PULS 4 0 (0.0) 0 (0.0) PULS 5 0 (0.0) 0 (0.0) Clavien-Dindo 0.926 No complications 46 (92.0) 89 (89.9) Grade 1 3 (6.0) 8 (8.1) Grade 2 0 (0.0) 1 (1.0) Grade 3a 1 (2.0) 1 (1.0) Values are presented as mean ± SD or frequency (%) Comparison of demographic and clinical characteristics of the groups Values are presented as mean ± SD or frequency (%) A multivariable logistic regression analysis was performed to evaluate the association between body mass index (BMI), stone volume, smoking status, hydronephrosis, and DM and successful scope passage of the stone (Table  2 ). The dependent variable was coded as 1 = successful scope passage to the stone and 0 = access failure. Table 2 Characteristics of the study groups and results of the multivariable logistic regression analysis Predictor Variable 95% CI 95% CI OR Lower limit Upper limit p -value Age (per year) 1.012 0.978 1.047 0.412 BMI (per kg/m²) 1.107 0.964 1.272 0.149 Stone volume (mm³) 1.000 0.999 1.002 0.620 Smoking (yes vs. no) 0.609 0.265 1.400 0.243 Hydronephrosis (Grade 1–2 vs. none) 1.360 0.464 3.991 0.575 Hydronephrosis (Grade 3–4 vs. none) 1.364 0.316 5.897 0.677 Diabetes Mellitus (yes vs. none) 0.188 0.078 0.453 < 0.001 Dependent variable: ureteral access success (1 = successful scope passage to the stone, 0 = failure). An OR < 1 indicates a lower likelihood of successful stone access. Reference categories: non-smokers, no hydronephrosis, and the non-diabetic group. The model, including age as a covariate, remained statistically significant (χ² = 18.302, p  = 0.006; Nagelkerke R² = 0.173). Results were considered statistically significant when the 95% CI of the OR did not include 1. OR odds ratio, CI confidence interval Characteristics of the study groups and results of the multivariable logistic regression analysis Dependent variable: ureteral access success (1 = successful scope passage to the stone, 0 = failure). An OR < 1 indicates a lower likelihood of successful stone access. Reference categories: non-smokers, no hydronephrosis, and the non-diabetic group. The model, including age as a covariate, remained statistically significant (χ² = 18.302, p  = 0.006; Nagelkerke R² = 0.173). Results were considered statistically significant when the 95% CI of the OR did not include 1. OR odds ratio, CI confidence interval The overall model was statistically significant (χ² = 18.302, p  = 0.006), indicating that the included predictors significantly contributed to distinguishing between successful and unsuccessful scope passage to the stone. The model explained about 17.3% of the variance (Nagelkerke R² = 0.173), and the overall classification accuracy reached 78.7%. Sensitivity was 95.7% and specificity was 22.9%. When age was included as a covariate in the multivariable logistic regression model, DM remained a significant independent predictor of unsuccessful scope passage to the stone (Wald = 13.833, p  < 0.001). Conversely, age did not show a statistically significant independent effect ( p  = 0.412). This indicates that the impact of DM on access is independent of age-related clinical factors. Multivariable logistic regression analysis demonstrated that DM was the only independent factor significantly associated with a reduced likelihood of successful stone access (OR = 0.188, 95% CI 0.078–0.453, p  < 0.001). Patients with DM were significantly less likely to successfully access the stone, indicating a substantial, statistically significant contribution of this variable to the model (Wald = 13.833, p  < 0.001; OR = 0.188, 95% CI [0.078, 0.453]). Other predictors (stone volume, BMI, smoking, and hydronephrosis) were not statistically significant, as shown by Wald values and p-values.

This study was approved by the Samsun University Non-Interventional Clinical Research Ethics Committee with protocol code GOKAEK 2024/2/10. It was conducted in accordance with the ethical principles defined in the Declaration of Helsinki. The study was planned as a retrospective cohort study. Given the retrospective design, the ethics committee waived the need for informed consent. Given the retrospective observational design, formal prospective protocol registration was not performed. However, the study protocol—including inclusion and exclusion criteria, primary outcome definitions, and the statistical analysis plan—was defined prior to data extraction and approved by the institutional ethics committee. Transparency and methodological rigor were ensured through predefined outcomes, standardized data extraction procedures, and reporting in accordance with the STROBE (Strengthening the Reporting of Observational Studies in Epidemiology) recommendations. Between February 2024 and August 2024, a total of 149 patients, including 50 with DM (Group 1) and 99 without DM (Group 2), who underwent URS for ureteral calculi were included in the study. Patients with a documented diagnosis of DM who were receiving regular antidiabetic treatment were included in the study. Diabetes mellitus was therefore recorded as a binary variable (presence or absence). Due to the retrospective nature of the study and heterogeneity in outpatient follow-up, detailed data on glycemic control parameters, such as HbA1c levels, diabetes duration, and treatment modality, were not consistently available and could not be reliably analyzed. The retrospective cohort consisted of all consecutive adult patients who underwent ureteroscopic lithotripsy (URS) for ureteral stones at our institution during the predefined study period. Consecutive inclusion was applied to minimize selection bias, and patients were excluded only according to predefined criteria (previous ureteral surgery, solitary kidney, oncologic disease, pregnancy, diagnostic URS, or incomplete medical records). No additional subjective or outcome-based selection was performed. The sample size was determined based on a power analysis. Patients aged 18 to 80 years who were scheduled for surgery for ureteral calculi in our hospital were included in the study. Patients with any systemic disease other than DM, patients who had previously undergone surgery for kidney stones or ureteral calculi, patients who had previously undergone diagnostic URS, pregnant women, patients with oncologic diseases, and patients with one kidney were excluded. Detailed history and physical examination, routine preoperative laboratory tests, urinalysis and urine culture, direct urinary tract radiography, and non-contrast computed tomography using a stone protocol were retrospectively analyzed in all patients in whom URS was planned for treatment of ureteral calculi. Preoperative hydronephrosis grading was classified according to the Society of Fetal Urology (SFU). Stone volume was calculated from non-contrast computed tomography (CT) images using the ellipsoid formula: Volume = π/6 ​×(length×width×height). Where the stone dimensions were obtained in three orthogonal planes. In addition, the maximum stone diameter (mm) was recorded for each patient to complement the assessment of total stone burden. This method has been widely used in previous urolithiasis studies and provides a reliable approximation of true stone burden. These parameters were used to evaluate the potential relationship between stone burden and ureteral access difficulty. After preoperative preparation, URS was performed under general anesthesia in the operating room. All ureteroscopic procedures were performed by two experienced endourologists, each with more than ten years of surgical experience and a case volume exceeding 500 ureteroscopic procedures. Both surgeons followed the same standardized technique and operative protocol to minimize inter-operator variability and ensure procedural consistency. Resident physicians were involved only in assistance and perioperative care, not as primary operators. An intravenous 3rd-generation cephalosporin was given prophylactically 30 min before surgery. All patients had negative urine cultures before the procedure [ 3 ]. In the dorsal lithotomy position, the surgical field was disinfected twice with 10% povidone-iodine solution and covered with sterile drapes. The bladder was emptied with a 16 Fr bidirectional Foley catheter. Isotonic saline was used for irrigation. An 8 Fr rigid ureteroscope (4 Fr–8 Fr single-channel ureteroscope, Karl Storz, Germany) was inserted into the bladder via the urethral route. The 8 Fr specification refers to the maximum outer diameter of the ureteroscope shaft, including the distal tip, as defined by the manufacturer, and was used in accordance with contemporary European Association of Urology (EAU) guideline recommendations regarding ureteroscope caliber [ 3 ]. Routine cystoscopy was performed to evaluate the bladder mucosa and bilateral orifices. A hydrophilic guidewire (ZIPwire Hydrophilic Guidewire, 0.038 inch, Boston Scientific, USA) was passed through the rigid URS through the ureteral orifice on the side of the procedure into the renal collecting system. All URS procedures were performed with a safety guidewire. With the guidewire in place, the rigid URS was advanced through the ureteral orifice. The rigid URS was advanced with a guidewire to the segment containing the ureteral stone. Ureteral access success was defined as the successful advancement of the semirigid ureteroscope to the stone location with direct endoscopic visualization. If the stone could not be visualized directly by rigid URS due to distal stenosis, successful scope passage to the stone was considered unsuccessful, and the ureter was classified as difficult. In cases where the ureteroscope could not be advanced due to distal ureteral narrowing, no active mechanical dilation was attempted. Instead, passive dilation was achieved by placing a JJ stent, and re-intervention was planned after adequate dilation. Flexible ureteroscopy was not employed in these cases, as the primary objective of the study was to evaluate ureteral access success specifically in patients undergoing rigid ureteroscopy. This operational definition of “unsuccessful scope passage to the stone” is consistent with previous descriptions of the “difficult ureter” in the literature, where failure is defined as the inability to advance a semirigid ureteroscope beyond a stenotic segment [ 11 , 12 ]. In patients with successful stone access, the stone was removed, and then a 4.8 Fr or 6 Fr JJ stent was placed. Following successful ureteroscopic access, a JJ ureteral stent was routinely placed to prevent postoperative ureteral edema, facilitate adequate urinary drainage, and reduce the risk of obstruction or renal colic. Although current guidelines support selective stent placement, the standardized use of postoperative stenting in this cohort reflected institutional practice during the study period. It ensured procedural consistency while minimizing postoperative variability. A 270 μm holmium YAG laser fiber (Singleflex holmium laser fiber, Dornier MedTech, Germany) and Holmium: YAG laser (Dornier Medilas H Solvo, Dornier MedTech, Germany) were used for stone fragmentation. Patients were evaluated for stone-free status by imaging methods on postoperative days 1 and 30. The postoperative stone-free rate in our study was evaluated using non-contrast CT performed on postoperative day 30. CT imaging was selected because it offers the highest sensitivity and specificity for detecting residual fragments compared with ultrasound or Kidney, Ureter, Bladder (KUB) radiographs. The stone-free state was defined as the complete absence of any residual calculi or the presence of clinically insignificant fragments smaller than 3 mm [ 13 ]. This threshold is widely accepted in endourological outcome studies, as fragments below this size are unlikely to cause symptoms or require further intervention. The IBM Statistical Package for the Social Sciences (SPSS) version 25 was used for statistical analysis of the study. Categorical variables are presented as frequency (%). Continuous variables are presented as mean ± standard deviation. The conformity of the variables to normal distribution was evaluated using the Shapiro-Wilk test. Differences between independent groups were evaluated using the Student-t test and the Mann-Whitney U test. The relationship between categorical variables was evaluated using Chi-square tests. A multivariable logistic regression model was applied to evaluate factors predicting successful passage of the stone through the scope. In all statistical analyses, p-values less than 0.05 were considered statistically significant.

In this retrospective cohort, DM was significantly associated with a lower rate of successful scope passage to the stone during ureteroscopy. This association persisted after adjustment for relevant clinical variables, suggesting that DM may be an independent predictor of ureteroscopic access difficulty. These findings may be explained by diabetes-related alterations in ureteral smooth muscle structure and peristaltic function, which can adversely affect ureteral compliance. From a clinical perspective, awareness of a potentially difficult ureter in patients with diabetes may facilitate more tailored preoperative evaluation and surgical planning, including consideration of preventive strategies when appropriate. However, given the limitations of the study—particularly baseline imbalances between groups, limited sample size, and its retrospective design—these results should be interpreted with caution and require validation in larger, prospective, and methodologically robust studies.

Urinary tract stone disease is an important health problem recognized since ancient times and causes significant morbidity and an economic burden. Although it varies with various factors, its prevalence is estimated to be between 1% and 20%. In the last 20 years, both prevalence and recurrence rates have increased with industrialization, changes in dietary habits, and lifestyle [ 14 ]. The high prevalence and recurrence rates of stone disease worldwide have led to a need for higher stone-free rates and lower treatment complications [ 14 ]. If left untreated for a long time, ureteral calculi may lead to serious complications, including acute pyelonephritis and irreversible deterioration in renal function. Complications arising from ureteral calculi can be prevented by performing URS at the appropriate time [ 3 ]. Urologists may encounter narrow and difficult ureters during ureteroscopy. Preoperative stenting and medical treatments have been shown to facilitate access by shortening URS duration, increasing the stone-free rate, and decreasing the risk of ureteral injury. The presence of a ureteral stricture not only prevents spontaneous stone passage but also limits retrograde advancement of the endoscope. This condition, commonly known as a “difficult” or “tight” ureter, is defined as a state where semirigid advancement is obstructed by intrinsic or functional narrowing of the ureteral wall [ 11 , 12 ]. Using a definition consistent with prior descriptions of the “difficult ureter,” unsuccessful scope passage to the stone was attributed to a stenotic ureteral segment that prevented advancement of the semirigid ureteroscope. Defining the endpoint in this way ensures a standardized and reproducible assessment of access difficulty while avoiding potential iatrogenic trauma that may result from forced dilation, thereby enhancing the clinical validity and comparability of our findings. Choi et al. showed that DM induces hyperproliferation in ureteral smooth muscle cells, which is mediated by p-ERK/p-JNK/VEGF/PKC pathways. These changes decrease ureteral peristalsis, making stone excretion difficult and potentially reducing the success of endoscopic interventions. The concept of a “difficult ureter” reported by Imano et al. similarly supports the notion that structural changes in the ureteral wall and luminal stenosis are among the main factors affecting surgical success [ 15 ]. In the present study, the rate of successful scope passage to the stone was significantly lower in patients with DM compared to those without. Furthermore, multivariable analysis identified DM as the sole independent predictor negatively associated with access success. This suggests that diabetes may increase surgical difficulty by inducing morphologic and neuromuscular alterations in the ureteral wall, which could impair peristaltic function and consequently reduce both access and stone-free rates. Despite baseline differences in age, BMI, and stone volume, multivariable analysis confirmed that DM was a robust independent predictor of successful scope passage to the stone. In contrast, age did not show a significant impact. This finding suggests that the adverse effect of diabetes on ureteral passage is not solely attributable to age-related changes in ureteral compliance. However, it may instead reflect diabetes-induced microstructural and neuromuscular alterations within the ureteral wall. Nevertheless, because the patients’ glycemic control status could not be analyzed, the precise severity of this independent effect could not be fully quantified. Such potential residual confounding should be addressed in future multicenter prospective studies. It should also be noted that DM is commonly accompanied by advanced age and increased BMI, both of which may partially mediate the observed association between diabetes and reduced ureteral access success [ 16 , 17 ]. Although the regression model demonstrated high sensitivity, its low specificity likely reflects the inherent class imbalance in small retrospective cohorts. This finding underscores the need for larger, balanced datasets to improve predictive performance. Imano et al. examined the relationship between DM, hypertension, smoking, history of cardiovascular disease, and difficult ureter due to atherosclerosis of peripheral vessels in the ureteral wall. They found no increased risk of encountering a difficult ureter in patients with DM, in contrast to our study. Imano et al. argued that this was due to passive dilatation of the ureteral wall from increased urinary flow and neuropathy caused by polyuria in DM [ 12 ]. In our study, other clinical parameters, including stone volume, BMI, smoking status, and hydronephrosis, were included in the multivariable logistic regression analysis, and none were significantly associated with successful scope passage to the stone. This finding suggests that the specific effect of DM on ureteral structure is independent of other factors and more dominant than they are. Furthermore, although no significant difference in overall complication rates was observed between the groups, patients with diabetes mellitus may still be more susceptible to complications due to diabetes-related structural damage to the ureteral wall. Tailly et al. emphasized that infection rates after endoscopic stone surgery were significantly higher in patients with DM [ 18 ]. Similarly, El-Nahas et al. reported an increased incidence of febrile urinary infection after stone surgery in diabetic patients [ 19 ]. Diabetes is known to lead to micro- and macrovascular complications and impaired immune response [ 20 ]. This may increase the risk of mucosal trauma resulting in infection during ureterorenoscopy. In addition, decreased elasticity of glycosylated tissues in DM patients may predispose to delayed healing of the ureteral wall and, consequently, to a higher frequency of complications, such as perforation or stricture [ 21 ]. A recent systematic review confirmed that diabetes is significantly associated with postoperative infectious complications and adverse surgical outcomes following endourological procedures [ 13 ]. From a clinical perspective, in difficult ureteral cases encountered during ureteroscopy, active or passive dilatation methods may be preferred, and the operation may be postponed with preoperative stenting when necessary [ 22 , 23 ]. Therefore, being prepared for such possibilities, especially in patients with DM, is important for surgical success and for informing patients about possible complications. Careful evaluation of these patients before URS may provide urologists with a significant advantage in preoperative planning. A primary limitation is the lack of detailed diabetic parameters, such as disease duration and indices of long-term metabolic control. This prevented a more granular analysis of how the severity of diabetes correlates with the difficulty of successful scope passage to the stone, as chronic hyperglycemia is known to influence ureteral compliance through microvascular and neuromuscular alterations [ 24 , 25 ]. Furthermore, the potential influence of baseline imbalances between the study groups warrants consideration. Although variables such as age, BMI, and stone volume were included in the multivariable logistic regression model, residual confounding cannot be entirely excluded. These parameters are themselves known predictors of ureteral access difficulty and may have contributed to the observed differences in access success. Due to the retrospective nature and modest sample size of our study, we were unable to perform propensity score matching (PSM), which might have better balanced these baseline characteristics. Therefore, our results should be interpreted with caution, as the independent effect of DM on ureteral access may have been overestimated. Future large-scale prospective or PSM-based studies are warranted to validate our findings and better delineate the causal relationship. Although our findings suggest a significant association between DM and reduced ureteral access success, several limitations should be acknowledged. Due to the study’s retrospective design, auxiliary procedures, long-term ureteral complications, and postoperative renal functional outcomes could not be systematically evaluated. These parameters may provide additional insight into the broader clinical impact of difficult ureteral access, particularly in diabetic patients. Therefore, future prospective studies with longer follow-up periods should incorporate long-term ureteral patency, renal functional outcomes, and the need for auxiliary interventions better to characterize the clinical consequences of diabetes-related ureteral alterations. Another limitation of the present study is the lack of detailed operative laser parameters, such as laser power, pulse energy, frequency, total laser time, or total delivered energy. Due to the retrospective design, these variables were inconsistently documented and could not be analyzed. Although the primary focus of this study was ureteral access success rather than stone fragmentation efficiency, standardized reporting of laser settings may provide additional insight into procedural complexity and surgical outcomes. Future prospective studies should incorporate systematic recording of laser parameters to evaluate their potential impact on ureteroscopic performance better. Finally, another important limitation of this study is the small sample size, particularly in the DM group, which may have reduced the multivariable logistic regression analysis’s statistical power. Although the model demonstrated statistical significance, the relatively low Nagelkerke R² value (0.173) suggests that a substantial proportion of the variability in stone access success remains unexplained. In addition, the low model specificity (22.9%) indicates a limited ability to identify patients at risk of access failure accurately. These findings highlight the constraints of multivariable modeling in small retrospective cohorts and underscore that our results should be interpreted with caution. Larger, adequately powered prospective studies are required to validate these findings and improve the predictive performance of future models.

Urinary tract stone disease is an increasing and widespread health problem worldwide. Although its prevalence varies depending on environmental, dietary, and genetic factors, its lifetime prevalence ranges from 1% to 20%. It is most common between the ages of 20 and 50 [ 1 ]. Ureteral stones are seen as primary due to anatomical anomalies or more commonly as secondary after progression of renal stones to the ureter. Localization, size, and hardness of the stone are among the factors that determine the treatment method for ureteral stones. Treatment modalities such as extracorporeal shock wave lithotripsy (SWL), ureteroscopy (URS), and open/laparoscopic ureterolithotomy are used [ 2 ]. Today, minimally invasive methods are preferred due to advances in technology and instrumentation. Ureteroscopy is the most commonly used method for treating ureteral calculi. In the European urology guideline, URS or SWL is recommended for ureteral stones of 10 mm or smaller, and URS is recommended as the first-line treatment for stones larger than 10 mm [ 3 ]. Complications such as infection, ureteral trauma, perforation, bleeding, ureteral stricture, and stone migration may occur during and after ureteroscopy. Conditions such as tuberculosis, ureteral cancer, and endometriosis that may lead to ureteral stricture and decrease the rate of access to ureteral calculi should also be kept in mind. Routine stent placement before ureteroscopy is not recommended [ 4 ]. Diabetes mellitus (DM) is known to induce chronic microvascular damage, neuromuscular dysfunction, and connective tissue remodeling, which may adversely affect smooth muscle contractility and tissue compliance. These diabetes-related alterations can impair peristaltic activity and structural adaptability in hollow organs, suggesting a potential mechanism by which ureteral function and endoscopic access may be compromised [ 5 ]. Diabetes mellitus causes neurogenic, myogenic, and urothelial dysfunctions in the lower urinary system and may also manifest itself with smooth muscle hyperproliferation in the ureter. This may decrease ureteral peristalsis and make stone excretion difficult [ 6 ]. Although several studies have investigated the impact of DM on overall ureteroscopic outcomes—such as stone-free rates and postoperative infectious complications—these analyses have focused mainly on treatment success rather than on achieving ureteral access [ 7 , 8 ]. The successful advancement of a semirigid ureteroscope to the stone location represents a distinct and clinically relevant step that reflects ureteral compliance and anatomical adaptability rather than stone fragmentation success. Despite advances in miniaturized and flexible ureteroscopes, the phenomenon of the “difficult ureter” remains clinically relevant and is encountered in routine practice [ 9 , 10 ]. By focusing on ureteral access success as a primary outcome, the present study aims to address this gap in the literature and to explore whether DM independently predisposes patients to ureteroscopic access difficulty. In this study, we aimed to evaluate the impact of DM on operative outcomes by assessing successful scope passage to the stone during ureteroscopic lithotripsy.