How do you diagnose peritonitis in a Peritoneal Dialysis (PD) patient?

Diagnosis of Peritonitis in Peritoneal Dialysis Patients

The diagnosis of peritonitis in peritoneal dialysis (PD) patients requires a peritoneal fluid white blood cell (WBC) count ≥230/μL with >50% neutrophils, along with clinical symptoms such as abdominal pain, cloudy dialysate, and fever. 1

Diagnostic Criteria

Laboratory Testing

• Peritoneal fluid analysis:
  • Collect effluent dialysate using the "aliquot method":
    • Shake each bag of effluent vigorously
    • Empty into a measuring container
    • Record the volume
    • Take appropriate sample for laboratory testing 2
  • WBC count ≥230/μL provides optimal sensitivity (98%) and specificity (89%) 1
  • Neutrophil predominance (>50% of WBCs) 1
  • Culture of dialysate effluent (positive in approximately 80% of cases) 3

Clinical Presentation

• Cloudy dialysate - the most consistent sign
• Abdominal pain - may vary from mild to severe
• Fever - not always present but increases diagnostic certainty
• Nausea/vomiting - common accompanying symptoms
• Elevated C-reactive protein - supports diagnosis when present 1

Diagnostic Algorithm

1. Assess for cloudy dialysate and abdominal symptoms
2. Collect peritoneal fluid sample using aliquot method
3. Perform cell count and differential:
   • If WBC ≥230/μL with >50% neutrophils → Diagnose peritonitis
   • If WBC <230/μL without fever or elevated CRP → Peritonitis unlikely (99.8% sensitivity for exclusion) 1
4. Send for culture and sensitivity (aerobic, anaerobic, and fungal)
5. Initiate empiric antibiotics while awaiting culture results

Special Considerations

Culture-Negative Peritonitis

• Occurs in up to 20% of cases 3
• Consider:
  • Prior antibiotic exposure
  • Improper culture technique
  • Unusual organisms requiring special media
  • Non-infectious causes (chemical, eosinophilic)
  • Possible enteric source if symptoms persist despite antibiotics 4

Fungal Peritonitis

• Accounts for 3-6% of peritonitis episodes
• Risk factors:
  • Prior bacterial peritonitis (87.5% of cases)
  • Recent broad-spectrum antibiotic use 5
• Requires immediate catheter removal and antifungal therapy 2

Timing Considerations

• Do not perform peritoneal membrane function testing during or within 1 month after peritonitis, as results will be inaccurate due to temporary changes in transport characteristics 2
• Peritoneal transport increases during peritonitis and usually recovers within 1 month after resolution 6

Pitfalls to Avoid

1. Using outdated diagnostic thresholds - The traditional cutoff of 100/μL WBC has only 35% specificity; using 230/μL improves specificity to 89% without compromising sensitivity 1

2. Delaying diagnosis of enteric peritonitis - Persistent symptoms despite appropriate antibiotics should prompt investigation for intestinal sources (e.g., mesenteric ischemia, diverticulitis) 4

3. Missing fungal peritonitis - Consider fungal etiology in patients with recent antibiotic exposure and non-resolving or recurrent peritonitis 5

4. Performing membrane transport testing too soon - Wait at least 1 month after peritonitis resolution before assessing peritoneal membrane function 2