Instant Diagnosis of Peritoneal Dialysis- Associated Peritonitis: Validation of a Simple Bedside Microscopy Approach

Background: Peritoneal dialysis (PD)–related peritonitis remains a major cause of technique failure, morbidity, and mortality. Timely diagnosis is crucial, yet conventional white blood cell (WBC) quantification by flow cytometry (FCC) requires centralized laboratory processing, delaying treatment. This study aimed to validate a direct manual microscopic (DMC) method for bedside quantification of WBCs in peritoneal effluent as a rapid, low-cost diagnostic alternative. Methods: In this single-center study, 40 PD patients underwent 250 paired WBC assessments between January 2024 and June 2025. Peritoneal effluent samples were analyzed by both DMC and FCC at peritonitis onset, during treatment follow-up, and in asymptomatic controls. Diagnostic performance was evaluated using Spearman’s correlation, receiver operating characteristic (ROC) analysis, and the Youden index, employing FCC as the reference standard (>100 cells/μL). Results: Across all evaluations, DMC and FCC showed a strong correlation (ρ = 0.91, p < 0.0001). In patients evaluated for suspected peritonitis (n = 36), DMC achieved a sensitivity of 97.0% and specificity of 100% at a cut-off of 20 cells/20 HPFs (AUC = 0.99). During follow-up (n = 187), correlation remained high (ρ = 0.89, p < 0.0001), with sensitivity 97.2% and specificity 83.4% at 12 cells/20 HPFs (AUC = 0.97). Conclusion: DMC provides a reliable, rapid, and quantitative alternative to automated cytometry for diagnosing and monitoring PD-related peritonitis. Its simplicity, affordability, and bedside applicability make it particularly suitable for integration with home turbidity monitoring systems and for use in low-resource settings to improve timely peritonitis management.