Diagnostic Criteria for Peritoneal Dialysis-Related Peritonitis
The diagnosis of peritoneal dialysis (PD) related peritonitis requires a peritoneal fluid white blood cell (WBC) count of >100 cells/μL with >50% polymorphonuclear leukocytes (PMNs).
Diagnostic Criteria Components
Cell Count Thresholds
- Primary criterion: Peritoneal fluid WBC count >100 cells/μL 1
- Secondary criterion: >50% of these cells should be polymorphonuclear leukocytes (PMNs) 2
- Recent research suggests that increasing the WBC cutoff to 230/μL may improve specificity (89%) without compromising sensitivity (99.8%) when combined with assessment of inflammatory markers 1
Supporting Clinical Features
- Cloudy dialysate effluent (classic presentation)
- Abdominal pain or tenderness
- Fever
- Elevated C-reactive protein
Important Diagnostic Considerations
Timing of Cell Count Assessment
- Cell counts should be performed after an adequate dwell time
- Initial clear effluent does not rule out peritonitis, as WBC count may increase over time
- In suspected cases with clear effluent, repeat the cell count after 7-12 hours 3
Culture Requirements
- Bacterial culture should be performed to confirm diagnosis
- Cultures should be inoculated directly into blood culture bottles at bedside to increase yield from 50% to 80% 4
- A positive culture with WBC <100/μL represents "bacterascites" which may progress to peritonitis 5
Response to Treatment Patterns
- Early response: Average rate reduction of 68.4% per day in dialysate WBC
- Delayed response: Average rate reduction of 34.0% per day in dialysate WBC
- Treatment failure: Average rate reduction of only 14.2% per day in dialysate WBC 6
Pitfalls to Avoid
- Relying solely on appearance: Some cases present with acute abdomen but initially clear effluent 3
- Using only absolute WBC count: The percentage of PMNs (>50%) is more sensitive than absolute count alone 2
- Inadequate dwell time: Short dwell times may yield falsely low cell counts
- Delayed diagnosis: Each hour of delay in diagnosis increases mortality by 3.3% 5
- Waiting for culture results: Treatment should begin immediately after obtaining samples
Special Situations
- Post-peritonitis assessment: Wait at least 1 month after resolution of peritonitis before performing peritoneal membrane transport testing 5
- Peritonitis with clear effluent: Repeat cell count after several hours if clinical suspicion is high 3
- Culture-negative neutrocytic ascites: Treat similarly to culture-positive cases as they have similar morbidity and mortality 5
The prompt diagnosis and treatment of PD-related peritonitis is crucial for reducing morbidity and mortality. While the standard diagnostic criterion of >100 WBCs/μL with >50% PMNs remains widely accepted, clinicians should maintain a high index of suspicion in patients with typical symptoms even when initial cell counts are borderline.