The Diagnostic Role of Tumor and Inflammatory Biomarkers in Ascitic Fluid: A Systematic Review.

This systematic review was conducted to evaluate the diagnostic and prognostic performance of tumor and inflammatory biomarkers measured in ascitic fluid, with the aim of distinguishing malignant from inflammatory causes of ascites. This review included observational studies (retrospective or prospective), clinical comparison studies and biomarker validation studies evaluating tumor and inflammatory markers in ascitic fluid for the diagnosis of malignant or inflammatory ascites. Studies were excluded if they involved animals, were case reports, did not measure markers in ascitic or peritoneal fluid or were published in languages other than English. A comprehensive literature search was conducted using PubMed and Scopus databases. The search covered studies published between January 2014 and December 2024. The final search was carried out in May 2025, and reference lists of included studies were also screened to capture any additional eligible records. Searches used Boolean operators (AND/OR) to combine terms relating to ascitic or peritoneal fluid, tumor markers (e.g., CEA, CA125, CA19-9, HE4), inflammatory markers (e.g., CRP, IL-6, VEGF, TNF-α) and emerging biomarkers (e.g., microRNAs, exosomes, extracellular vesicle proteins). Filters were applied to limit results to human studies, English-language publications and the specified time frame. The complete search strategy, including all terms and combinations used are shown in Appendix A . Reviewers conducted an initial screening of titles and abstracts to determine the preliminary eligibility of studies. Full-text screening was then performed for the selected studies. To minimize selection bias, a random subset of included and excluded studies were independently re-evaluated. Any uncertainties or discrepancies were resolved by consulting a senior researcher or by referring to the predefined inclusion criteria. The study selection process was documented using the PRISMA 2020 flow diagram ( Figure 1 ), created using the official tool available at www.prisma-statement.org [ 14 ]. Findings from the eligible studies were synthesized narratively. A formal meta-analysis of diagnostic accuracy was not performed because the included studies varied substantially in design (retrospective vs. prospective and case–control), patient selection and disease spectrum, assay platforms and cutoff thresholds. These methodological differences precluded valid pooling of sensitivity/specificity or AUC across studies. Instead, results are presented as study-level estimates and typical ranges to facilitate transparent comparison. Data from the included studies were extracted using a standardized form. The following information was collected: Study characteristics (author, year, country, sample size, age, duration and setting); Type of marker(s) evaluated (tumor and inflammatory); Fluid analyzed (ascitic fluid); Diagnostic performance (sensitivity, specificity and AUC, if available); Prognostic significance (if available); Study design (e.g., prospective, retrospective). Study characteristics (author, year, country, sample size, age, duration and setting); Type of marker(s) evaluated (tumor and inflammatory); Fluid analyzed (ascitic fluid); Diagnostic performance (sensitivity, specificity and AUC, if available); Prognostic significance (if available); Study design (e.g., prospective, retrospective). Risk of bias for all 42 included studies was evaluated using the ROBINS-I framework. A traffic light plot was generated using the robvis web application developed by McGuinness and Higgins [ 15 ], providing a visual summary of bias across each domain. Diagnostic performance was summarized using standard measures, such as sensitivity, specificity and area under the ROC curve (AUC). When available, diagnostic odds were also reported. Due to methodological heterogeneity and varying diagnostic endpoints, a narrative synthesis of results was performed. Data were organized into thematic tables, classified by marker type (tumor markers or inflammatory markers). A meta-analysis was considered but not performed due to heterogeneity across study design and reporting metrics. Visual summaries, including performance tables and heatmaps, were constructed to illustrate diagnostic performance across different marker categories and fluid types. This systematic review was conducted in accordance with the PRISMA 2020 guidelines for reporting a systematic review [ 14 ]. The review was not prospectively registered. Ethical approval was not required, as this study involved secondary analysis of previously published data. Generative AI tools were used in a limited capacity to assist with data interpretation and figure formatting under direct author supervision.

Ascites, defined as an abnormal accumulation of fluid in the peritoneal cavity, is a clinical sign commonly associated with underlying conditions, such as liver cirrhosis, cardiac dysfunction, renal impairment, infections and malignancies [ 1 ]. Although its presence is generally linked to poor prognosis [ 2 , 3 ], patient outcomes depend on the cause. Accurate diagnosis requires the integration of ascitic fluid analysis with clinical and pathological evaluation [ 4 ]. Traditional classifications based on total protein content in ascitic fluid have shown limited diagnostic reliability [ 4 , 5 ]. The introduction of the serum-ascites albumin gradient (SAAG) improved the differentiation between portal hypertension-related and non-portal causes of ascites, including peritoneal inflammation and malignancy [ 4 ]. However, when cytology is inconclusive, the SAAG alone may be insufficient for definitive diagnosis. In recent years, tumor and inflammatory biomarkers in ascitic fluid have gained attention as supplementary tools to help determine the etiology of ascites. Tumor markers, which are molecules produced by tumor cells or by the host in response to tumor presence, are widely used in oncology for screening, diagnosis, monitoring treatment response and prognosis [ 6 ]. Their application in ascitic fluid analysis may offer additional diagnostic value when conventional methods are insufficient. Several tumor markers, such as alpha-fetoprotein (AFP), carcinoembryonic antigen (CEA), cancer antigen (CA) 19-9 and CA 125 have been studied for their potential to differentiate between malignant and non-malignant ascites. Many reports have shown that these markers are often elevated in ascitic fluid in cases of hepatocellular carcinoma or gastrointestinal and ovarian cancers [ 5 , 7 , 8 , 9 , 10 , 11 ]. The proteomic analysis of ascitic fluid has also been explored as a strategy to identify novel biomarkers in hepatocellular carcinoma [ 12 ]. Some studies have demonstrated that measuring tumor markers in serum or ascitic fluid may help distinguish malignant ascites. However, small sample sizes and inconsistent marker selection have limited the strength of these findings [ 6 ]. As a result, the diagnostic value of these markers in ascites remains under debate. Inflammatory biomarkers have also been investigated for their potential to clarify the underlying cause of ascites. Markers such as C-reactive protein (CRP), vascular endothelial growth factor (VEGF), lactate dehydrogenase (LDH) and several interleukins have been studied in this context. Among these, LDH and VEGF have shown stronger associations with malignant ascites [ 4 , 6 ]. There remains a debate regarding whether ascitic or serum levels provide more clinically meaningful information. Ascitic fluid may better reflect local inflammation, whereas serum levels may indicate systemic processes [ 13 ]. VEGF, in particular, is often significantly elevated in malignant ascites, supporting its utility as a potential localized tumor marker [ 4 ]. This systematic review aimed to evaluate the diagnostic and prognostic performance of tumor and inflammatory markers measured in ascitic fluid, with a focus on their role in distinguishing malignant, infectious and inflammatory causes of ascites. The review addressed the following research questions: Do tumor markers measured in ascitic fluid offer clinically useful diagnostic and prognostic accuracy for malignant ascites? Are inflammatory markers in ascitic fluid effective in differentiating between inflammatory and malignant ascites? Does combining tumor and inflammatory markers enhance the ability to distinguish between malignant and non-malignant ascites? Do tumor markers measured in ascitic fluid offer clinically useful diagnostic and prognostic accuracy for malignant ascites? Are inflammatory markers in ascitic fluid effective in differentiating between inflammatory and malignant ascites? Does combining tumor and inflammatory markers enhance the ability to distinguish between malignant and non-malignant ascites? Hypothesis: We hypothesized that biomarkers measured directly in ascitic fluid would demonstrate sufficient diagnostic and prognostic utility for differentiating between malignant and inflammatory ascites, due to their ability to reflect localized disease activity within the peritoneal cavity. Ongoing debate regarding the clinical utility of tumor and inflammatory markers in ascitic fluid supports the need to evaluate their diagnostic performance in this review. Following the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines [ 14 ], this review synthesized current evidence to evaluate the clinical value of ascitic biomarkers and support their application in diagnostic workflows.

The systematic search identified a total of 1611 records across all databases. After duplicate removal, 1608 articles remained for title and abstract screening. Of these, 72 full-text articles were assessed for eligibility. In total, 42 studies met the inclusion criteria and were included in the final analysis. The screening process is illustrated in Figure 1 (PRISMA flow diagram). Full-text articles were excluded due to insufficient data on ascitic or serum tumor marker levels, exclusive focus on tissue or cytology, case report format or lack of relevance to the review scope. Following a comprehensive screening process, 42 studies were included in this review ( Table 1 ). The included studies were heterogeneous in design, population and laboratory methodology, which limited the feasibility of quantitative synthesis and made direct comparison between studies difficult. These studies were geographically diverse and represented a range of clinical settings, including oncology centers, academic hospitals and multicenter consortia. Sample sizes varied from 22 to over 1000 patients, with most study populations ranging in age from 50 and 70 years. Most studies focused on adults with suspected malignant, infectious or inflammatory ascites. Prospective observational studies were among the most common, even though several high-quality retrospective cohorts and diagnostic validation studies were also included. This variation in study design and setting increases the breadth of the evidence base but also adds complexity when interpreting pooled diagnostic performance. Risk of bias across the included studies was evaluated using the ROBINS-I tool [ 15 ]. The overall judgments were presented in a corresponding traffic light plot ( Figure 2 ). Across the 42 included studies, the overall methodological quality was acceptable, with none rated as high risk of bias. However, several domains consistently raised concerns. Blinding was rarely feasible, as ascitic fluid was collected in clinical contexts where the underlying diagnosis was already suspected; accordingly, blinding of participants and personnel was judged unclear in 39 studies, and outcome assessment was judged unclear in 38 and high in one. Retrospective designs, which comprised much of the evidence base, further limited standardized follow-up and increased susceptibility to spectrum bias, particularly in small single-center or case–control cohorts. In contrast, incomplete outcome data and selective reporting posed little risk, with 41 studies rated low for completeness, and all judged low for reporting transparency. Random sequence generation and allocation concealment were not applicable to the observational designs. Overall, these patterns explain why all studies were classified as having “some concerns”, reflecting limitations in design and blinding rather than systematic flaws in reporting or laboratory methods. Tumor markers were analyzed in a range of biological fluids as presented in Table 2 , most commonly in ascitic fluid, though several studies also included peritoneal or pleural fluid. Among the 30 studies that investigated tumor markers, the ones most frequently measured were CEA, CA125 and CA 19-9, while less commonly investigated markers included HE4, CA72-4, CA 15-3 and CYFRA 21-1 ( Figure 3 ). A few studies explored novel candidates such as autotaxin (ATX) and microRNAs. Sensitivity, specificity and AUC values for selected biomarkers and biomarker combinations is presented in Figure 4 . CEA was generally among the best-performing single ascitic markers, with accuracy varying by tumor type and cohort. Its value was most evident in cancer-specific cohorts, such as colorectal cancer, where Song et al. [ 39 ] reported an AUC of 0.996 for ascitic CEA. High accuracy was also observed in mixed malignancy cohorts when incorporated into diagnostic algorithms [ 20 , 32 ]. In broader heterogenous populations, single-marker CEA performance was more modest (AUCs generally ~0.78–0.86), but its utility increased substantially in combination with other markers, such as CA19-9 and CA125, or when applied in ascitic-to-serum ratio models. These multi-marker approaches frequently achieved sensitivities and specificities above 85–95%, underscoring the added value of integrated strategies over single-marker testing. CA 125 and CA 19-9 showed diagnostic utility when interpreted together or used in ratio-based models. In patients with pseudomyxoma peritonei, elevated tumor marker counts (including CA125, CA19-9, and CEA) were linked to poorer surgical outcomes and reduced survival [ 31 , 47 ]. Among the less-frequently studied markers, HE4 showed high specificity though with limited sensitivity, ATX was associated with advanced-stage ovarian cancer and reduced disease-free survival, with one study reporting an AUC of 0.842 [ 18 ], while a microRNA ratio (miR-21/miR-223) achieved an AUC of 0.982 for differentiating malignant from non-malignant ascites [ 38 ]. While not all studies assessed prognosis, several found that higher biomarker levels were associated with advanced disease or poorer clinical outcomes [ 20 , 30 ], indicating potential roles beyond diagnosis in treatment stratification and prognostic assessment. Twelve studies assessed inflammatory markers in ascitic or peritoneal fluid, with many also comparing them to serum levels ( Table 3 ). Frequency of inflammatory marker usage across studies is presented in Figure 5 . The most frequently assessed were C-reactive protein (CRP), interleukin-6 (IL-6), tumor necrosis factor-alpha (TNF-α) and vascular endothelial growth factor (VEGF), either alone or as part of diagnostic panels. CRP showed consistent diagnostic value; for example, Abdel-Razik et al. [ 13 ] reported AUCs of 0.842 in ascitic fluid and 0.821 in serum, with the highest accuracy when combined. Yüksel et al. [ 52 ], likewise, found ascitic CRP to be superior to serum for distinguishing malignant from benign ascites. In postoperative settings, elevated peritoneal CRP predicted early anastomotic leakage [ 34 ] though its role in malignancy remains limited. IL-6 demonstrated strong diagnostic and prognostic potential, reaching an AUC of 1.000 in ovarian cancer when used alone or with VEGF-A [ 46 ] and was associated with poorer survival when elevated alongside TNF-α [ 30 ]. VEGF levels were consistently higher in malignant ascites, with reported AUCs ranging from 0.94 to 1.000 across multiple studies, while serum VEGF also showed diagnostic utility (AUC 0.921) [ 13 ]. Less frequently assessed markers also offered insight: MMP-9 in combination with CRP aided in detecting postoperative complications [ 34 ], whereas the VEGF levels in ascitic fluid were associated with disease progression and stage in ovarian cancer [ 31 ]. Overall, inflammatory markers provided the greatest diagnostic value when used in combination, reflecting local immune and vascular changes and complementing tumor markers in differentiating malignant ascites from infectious or reactive causes. A diagnostic algorithm was developed to summarize the main findings of this review into a clinically applicable framework ( Figure 6 ). It presented a structured approach to evaluating ascites, beginning with fluid collection and standard biochemical analysis. Based on the suspected underlying cause, selected tumor or inflammatory markers could then be applied to improve diagnostic accuracy. Although ascitic fluid was preferred due to its proximity to peritoneal pathology, alternative sampling methods such as peritoneal washings were considered in patients without free fluid. Some studies also examined the use of composite indices or statistical models, which suggested added diagnostic value in selected cases. Figure 7 supports the algorithm by illustrating marker performance and cancer-type comparisons using AUC-based visual summaries.

This systematic review followed PRISMA guidelines and aimed to evaluate the diagnostic and prognostic value of tumor and inflammatory markers in ascitic and related peritoneal fluids. A total of 1611 records were identified through searches across major databases. After removing duplicates and completing title, abstract and full-text screening, 42 studies met the inclusion criteria ( Figure 1 ). Studies were excluded for focusing on serum-only marker measurements, tissue or cytology-based findings, case reports, plasma-only analyses or for using non-standard methods such as reverse transcription polymerase chain reaction (RT-PCR) on lavage samples. One exception was the study by Massoumi Moghaddam et al. [ 33 ], which examined IL-6 in tumor tissue, but was included due to its relevance in predicting post-treatment ascites. The included studies were conducted in oncology centers [ 18 , 20 , 38 ] and academic hospitals [ 36 , 48 ] and used a variety of designs including prospective, retrospective and cross-sectional formats. Sample sizes ranged from 22 participants in the study by Kolomeyevskaya et al. [ 30 ] to over 1000 in Trapé et al. [ 44 ]. Most study populations included participants aged between 50 and 70 years. The differences in patient groups, study designs, fluid types, markers tested and how results were reported made it especially important to assess the risk of bias in a clear and structured way, as shown in Figure 2 . Data were presented in a baseline summary table ( Table 1 ). Many studies reported complete diagnostic metrics, including AUC, sensitivity and specificity, while others lacked full data. All relevant information was extracted when available; missing data were noted separately. Most studies assessed biomarkers in ascitic fluid. Serum measurements were included when both fluids were analyzed in the same study, as seen in Liu et al. [ 6 ], Abdel-Razik et al. [ 13 ] and Yu et al. [ 51 ]. Some studies evaluated peritoneal or pleural fluid when ascitic fluid was absent. For example, Yamamoto et al. [ 49 ] and Jain et al. [ 24 ] measured CEA and CA72-4 in intraoperative peritoneal washings, especially in early-stage gastrointestinal cancers, where cytology alone was inconclusive. Among tumor markers, CEA, CA125 and CA19-9 were the most commonly studied. CEA consistently showed strong performance, with Song et al. [ 39 ] reporting an AUC of 0.996 in colorectal cancer and similarly high values observed in ovarian cancer by Du et al. [ 20 ] and Liu et al. [ 6 ]. These markers performed better when used in combination or when interpreted using ascitic-to-serum ratios, as demonstrated by Trapé et al. [ 44 ] and Tong et al. [ 43 ]. Figure 3 displays the frequency of tumor marker use across the included studies. Figure 4 summarizes the diagnostic performance of selected markers and marker combinations. Twelve studies evaluated inflammatory markers such as CRP, IL-6, VEGF and TNF-α. These markers were most useful when applied to clinical decision-making, particularly in distinguishing malignant ascites from benign or infectious causes. Abdel-Razik et al. [ 13 ] found that CRP measured in ascitic fluid had higher diagnostic accuracy (AUC 0.842) compared to serum CRP (AUC 0.821). V. Dalal et al. [ 46 ] reported that IL-6 and VEGF combined reached an AUC of 1.000 in the diagnosis of ovarian cancer. Kolomeyevskaya et al. [ 30 ] associated elevated IL-6 and TNF-α levels in ascitic fluid with reduced progression-free survival. In a surgical setting, Mužina Mišić et al. [ 34 ] showed that CRP in peritoneal drain fluid predicted early anastomotic leakage. Figure 5 shows the frequency of inflammatory marker use across different fluid types. A proposed diagnostic algorithm ( Figure 6 ) integrates these findings into a practical framework to support clinical evaluation. Emerging markers provide additional, though preliminary, insights. HE4 offered high specificity but limited sensitivity, particularly in ovarian cancer [ 36 ]. ATX achieved an AUC of 0.842 and was linked to worse survival [ 18 ]. MicroRNA profiles such as the miR-21/miR-223 ratio reached very high accuracy (AUC 0.982) [ 38 ], while Záveský et al. [ 53 ] demonstrated the potential of MSLN in epithelial ovarian cancer. However, evidence for these markers is restricted to small, often retrospective studies without external validation. Their role remains investigational and requires prospective multicenter confirmation before integration into clinical practice. The results confirmed that ascitic fluid provided valuable diagnostic information in patients with suspected malignancy and often outperformed serum. Measurements of tumor and inflammatory markers in ascitic fluid provided strong diagnostic support across gastrointestinal and ovarian cancers. These markers performed best when interpreted in combination or through fluid-to-serum ratios [ 32 , 44 ]. Inflammatory markers, although less specific, added important context by reflecting local immune and vascular processes. For example, ascitic CRP showed higher diagnostic accuracy than serum CRP in differentiating malignant from benign ascites [ 13 , 52 ]. Cytology remains the diagnostic standard, but several studies demonstrated that tumor or inflammatory markers improved diagnostic clarity when cytologic findings were inconclusive [ 24 , 49 , 51 ]. In situations where ascites was absent, peritoneal washings or lavage fluid were also diagnostically useful, with CA72-4 and CEA measured reliably to support decision-making in early-stage disease [ 24 , 49 ]. This highlighted the methodological diversity across studies, where even alternative fluid sources could expand diagnostic options. Collectively, these findings indicated that ascitic fluid biomarkers complemented existing diagnostic tools and helped address gaps in clinical practice. As outlined in the preceding section, ascitic biomarkers consistently demonstrate diagnostic and prognostic value that extends beyond the limitations of cytology. In daily practice, cytology is often negative or inconclusive despite a strong clinical suspicion of malignancy, creating delays in diagnosis and management. Biomarker testing proposes a practical solution in these situations. In gastric cancer, several groups have suggested that markers such as CEA, CA19-9 and CA125 in ascitic fluid may help reveal peritoneal involvement when cytology is negative, potentially supporting earlier therapeutic decisions [ 39 , 49 ]. In ovarian cancer, ascitic HE4 and CA125 have been proposed as useful adjuncts when cytology is inconclusive, with multiple studies reporting sensitivities above 80–90% [ 6 , 22 , 32 , 36 , 45 ]. Tong et al. [ 43 ] further indicated that CEA combined with CA125 could strengthen classification when cytology was inconclusive. Multi-marker approaches, as described by Du et al. [ 20 ], Jain et al. [ 24 ], Trapé et al. [ 44 ] and Bérgamo et al. [ 16 ] suggest that panels could provide greater confidence than cytology alone. In regions where tuberculosis complicates diagnosis, marker ratios and globulin indices have been proposed to help separate malignant from infectious ascites [ 51 ]. Inflammatory mediators may offer additional support. IL-6 and VEGF have been reported as indicators of malignant ascites [ 25 , 31 ], while models that included CA125 and CA72-4 appeared to improve classification beyond cytology alone [ 18 ]. CRP has been proposed as a practical adjunct, with studies suggesting its value in distinguishing malignant from benign effusions [ 13 , 52 ]. In surgical cohorts, peritoneal CRP has even been explored as a predictor of postoperative complications such as anastomotic leakage [ 34 ]. Our proposed diagnostic algorithm ( Figure 6 ) reflects these scenarios. Cytology remains the first-line diagnostic tool, but when results are negative or uncertain, biomarker analysis may provide additional guidance. In practice, this could mean supporting earlier recognition of peritoneal metastasis in gastric cancer, reducing repeated aspirations in ovarian cancer or even helping to distinguish malignancy from tuberculosis in atypical ascites. At the same time, biomarker cutoff values and assay thresholds varied substantially across studies; therefore, no universally accepted decision points have been validated. For this reason, the algorithm should be regarded as a conceptual framework rather than a prescriptive tool, with application tailored to assay-specific characteristics and local protocols. Emerging markers such as VCAM1, CD146 and CYFRA 21-1 remain exploratory but underline the need for prospective multicenter validation in real-world cohorts before biomarker-guided approaches can be confidently adopted in clinical practice. This review followed the PRISMA guidelines and included a broad range of studies with diverse geographic origins and methodological approaches, which strengthened its external validity. Data extraction was systematic and categorized by fluid type, marker category and diagnostic performance. Both established and emerging biomarkers were evaluated to reflect the current and evolving field of ascitic fluid diagnostics. However, the included studies differed significantly in design, marker thresholds and outcome reporting. Several studies did not report complete diagnostic metrics, and fluid sampling protocols varied. The use of peritoneal washings and lavage fluid may have introduced variability, although these methods reflect real-world clinical practice. Heterogeneity in study designs, assay methods, cutoff values, patient demographics and laboratory practices reduced comparability and may have influenced diagnostic accuracy. A structured risk-of-bias assessment was conducted using ROBINS-I, which identified recurring limitations. Most studies were rated as having some concerns, mainly due to the lack of blinding of patients and personnel, the retrospective design of many cohorts, variability in cutoff determination and incomplete follow-up. In many cases, blinding was not possible, as both patients and clinicians were aware of underlying diagnoses and the presence of ascites. Furthermore, small sample sizes and single-center recruitment were common, while only a few studies were multicenter or prospective. A more detailed interpretation of common bias domains, including limitations in blinding, retrospective design and threshold variability, is provided in Section 2.2 . The literature search was limited to PubMed and Scopus; while these cover the majority of biomedical research, the exclusion of databases such as Embase and Web of Science may have led to omission of additional relevant studies. Additionally, a formal meta-analysis could not be performed because of methodological heterogeneity; therefore, conclusions are based on a narrative synthesis of study-level findings. Several gaps identified in this review warrant further investigation. Although markers such as microRNAs, autotaxin and soluble PD-L1 demonstrate promising diagnostic performance in early studies, their use remains investigational and is not yet validated for routine clinical application. Standardized protocols for sample collection, storage and analysis were also needed. Second, very few studies compared different fluid types within the same group of patients. Future research should explore whether peritoneal or lavage fluids, when combined with serum markers, could reliably replace ascitic fluid when it is not available. Third, evidence on the use of ascitic biomarkers for longitudinal monitoring or treatment response remained limited. This represents a critical area for future research. Finally, malignancies such as hepatocellular carcinoma, gastric cancer and rare gynecological tumors were underrepresented in the current literature and require more focused investigation. Future studies should prospectively validate the proposed diagnostic algorithm in larger, multicenter cohorts using standardized assay platforms and predefined biomarker cutoffs. Such validation is essential to confirm its reproducibility and clinical utility before integration into routine practice.

This review highlighted that tumor and inflammatory markers in ascitic and related peritoneal fluids provided meaningful diagnostic and prognostic value. Markers such as CEA, CA125, IL-6 and VEGF consistently performed well, most notably when used in panels or as ratios with serum values. Importantly, ascitic fluid testing proved helpful in situations where cytology was inconclusive, or when serum markers alone lacked sensitivity, offering an earlier path to diagnosis and a clearer guide for patient management. For clinicians, these findings highlight that ascitic fluid biomarkers can complement established tools rather than replace them. By capturing local tumor activity and inflammatory changes directly within the peritoneal cavity, these markers provide information that serum testing may miss. This added layer of insight can support more confident treatment decisions, particularly in patients with suspected gastrointestinal or ovarian malignancies. Looking ahead, large prospective and multicenter studies are still needed to validate the clinical utility of both established and emerging biomarkers. Molecular and proteomic approaches show promise, but they remain at an early stage. Integrating ascitic fluid biomarkers into diagnostic pathways represents an important opportunity to connect laboratory medicine more directly with clinical care, with the ultimate goal of improving outcomes for patients with unexplained ascites. In summary, this review demonstrates that ascitic fluid biomarkers not only complement cytology but also open avenues for earlier, more accurate diagnosis and better-targeted treatment strategies. Their integration into diagnostic pathways could help reduce delays in management, particularly in oncology and infection, where timely decisions are critical. Future work should prioritize prospective, multicenter validation to confirm their utility and establish standardized diagnostic thresholds that will allow translation into routine clinical practice.