Optimal peritoneal fluid white blood cell count for diagnosis of peritonitis in peritoneal dialysis patients

BACKGROUND: The diagnosis of peritonitis among peritoneal dialysis (PD) patients is based on clinical presentation, dialysis effluent white blood cell (WBC) count, and dialysis effluent culture. Peritoneal fluid WBC count is very important in the initial diagnosis of peritonitis. The purpose of this work was to determine the optimal number of peritoneal WBCs with different clinical presentations at admission to define PD-related peritonitis. METHODS: Medical records of chronic PD patients who underwent work-up for suspected peritonitis between 2008 and 2019 were reviewed retrospectively. Results of all peritoneal WBC count tests during this period were collected. Clinical manifestations and follow-up analysis of each peritoneal WBC count were performed. RESULTS: The peritoneal WBC count cutoff of 100/μL recommended by International Society for Peritoneal Dialysis provided specificity of only 35%. Increasing peritoneal WBC count cutoff to 150, 200, and 250/μL provided sensitivity around 98% and gradually increasing specificity. The chi-square automatic interaction detector model of statistical analysis determined that peritoneal WBC count below 230/μL combined with absence of inflammatory markers (fever, increased C-reactive protein) ruled out peritonitis with 99.8% sensitivity. Peritoneal fluid WBC count cutoff of 230/μL provided specificity of 89% and good positive and negative likelihood scores of 8.3 and 0.03, respectively. Peritoneal fluid polymorphonuclear count has lower discriminating ability for peritonitis compared to peritoneal fluid WBC count. CONCLUSION: Increasing peritoneal fluid WBC count cutoff to 230/μL in suspected PD-related peritonitis could improve specificity without compromising the sensitivity of the test.