Diagnostic Criteria for PD-Associated Peritonitis
Yes, PD-associated peritonitis has distinct diagnostic criteria that differ from other forms of peritonitis—diagnosis requires meeting at least 2 of 3 specific criteria: clinical features consistent with peritonitis, dialysis effluent white blood cell (WBC) count >100 cells/μL, or positive effluent culture. 1
Standard Diagnostic Criteria
The International Society for Peritoneal Dialysis establishes that peritonitis is diagnosed when at least 2 of the following 3 criteria are present: 1
- Clinical features consistent with peritonitis (abdominal pain, cloudy effluent)
- Dialysate effluent WBC count >100 cells/μL (or >0.1 × 10⁹/L)
- Positive dialysate culture
Important Caveats About the WBC Threshold
Recent evidence suggests the traditional 100 cells/μL cutoff may be suboptimal. A higher threshold of 230 cells/μL provides significantly better specificity (89% versus 35%) while maintaining 98% sensitivity, particularly when combined with absence of inflammatory markers like fever or elevated C-reactive protein. 2 This higher cutoff reduces false-positive diagnoses without missing true peritonitis cases (negative likelihood ratio 0.03). 2
However, historical data shows that 10% of true peritonitis episodes present with initial WBC counts <100 cells/μL, and 15% show predominance of mononuclear rather than polymorphonuclear cells. 3 This means relying solely on cell counts can miss genuine cases—clinical judgment remains essential.
Key Differences from Other Peritonitis
PD-associated peritonitis diagnosis does not require peritoneal signs on physical examination or imaging findings, unlike secondary bacterial peritonitis from bowel perforation or other intra-abdominal catastrophes. 1 The cloudy dialysate effluent itself serves as direct sampling of the peritoneal cavity, making it a unique diagnostic advantage specific to PD patients.
Polymorphonuclear Cell Predominance
While traditionally emphasized, peritoneal fluid polymorphonuclear count has lower discriminating ability for peritonitis compared to total WBC count and should not be prioritized over total WBC assessment. 2
Timing Considerations for Testing
All diagnostic testing must be performed when the patient is clinically stable and at least 1 month after resolution of any previous peritonitis episode. 4 Peritonitis transiently increases peritoneal transport characteristics and can cause falsely elevated or depressed clearance measurements. 4
Culture Requirements
The proportion of culture-negative peritonitis should be ≤2% when pre-culture membrane filtration techniques are used. 3 Higher rates of negative cultures suggest inadequate laboratory techniques rather than true culture-negative disease.
Gram Stain Limitations
Gram stain results are consistent with final culture in only 28% of episodes and influence initial therapy in merely 7% of cases, making it a poor basis for treatment decisions. 3 Do not delay empiric antibiotic therapy awaiting Gram stain results.
Clinical Presentation Variability
Between 9-31% of peritonitis episodes would not meet diagnostic criteria if any single criterion (positive culture, WBC >100/μL, or clinical symptoms) were required alone. 3 This underscores why the "2 of 3" rule exists—no single finding is sufficiently sensitive or specific by itself.
Turbidity of dialysate effluent can serve as the sole criterion for initial diagnosis and treatment initiation while awaiting cell count and culture results. 3 Delaying treatment for laboratory confirmation risks worse outcomes.