How is catheter-associated peritonitis diagnosed?

Diagnosis of Catheter-Associated Peritonitis

Catheter-associated peritonitis in peritoneal dialysis is diagnosed by clinical presentation (abdominal pain, cloudy dialysate) combined with laboratory confirmation showing elevated white blood cell count (>100 cells/μL with >50% neutrophils) in peritoneal dialysate fluid and positive culture results from the dialysate.

Clinical Presentation

The diagnosis begins with recognizing key clinical features:

• Cloudy peritoneal dialysate effluent is the hallmark finding 1
• Abdominal pain and tenderness are common presenting symptoms 2
• Fever may or may not be present 1
• Physical examination should assess the catheter exit site for signs of local infection (erythema, purulence, tenderness) 3
• Palpate the catheter tunnel for tenderness or induration suggesting tunnel involvement 3

Laboratory Diagnosis

Peritoneal Dialysate Analysis

The definitive diagnostic approach requires:

• Cell count and differential from peritoneal dialysate effluent showing >100 white blood cells/μL with >50% polymorphonuclear cells 1
• Gram stain of the dialysate (though sensitivity is limited) 3
• Culture of dialysate fluid before initiating antibiotics to identify the causative organism 1, 4

Blood Cultures

• Obtain paired blood cultures (one peripheral, one from catheter) if catheter-related bloodstream infection is suspected 3
• Blood cultures help differentiate peritonitis from catheter-related bloodstream infection 5

Microbiological Confirmation

Culture the peritoneal dialysate effluent using appropriate techniques:

• Collect adequate volume (≥20 mL) for optimal yield 3
• Process samples promptly to maximize organism recovery 1
• The same organism should be identified from the dialysate to confirm the diagnosis 1

Assessment of Catheter Involvement

Physical Examination Limitations

Clinical examination alone is inadequate and insensitive for determining the extent of catheter tract involvement 6

Ultrasound Evaluation

• High-resolution ultrasound (≥7.5 MHz) along the catheter tunnel can detect subclinical tunnel infections 3, 6
• Ultrasound findings of pericatheter fluid collections indicate tunnel involvement, which occurs frequently with peritonitis even when not clinically apparent 6
• Ultrasound-guided strategy for early detection of complications decreases infection-related mortality in high-risk patients 3

Differential Diagnosis Considerations

Distinguishing from Catheter-Related Bloodstream Infection

If bloodstream infection is suspected alongside peritonitis:

• Use differential time to positivity (DTP): growth from catheter-drawn blood ≥2 hours before peripheral blood indicates catheter-related bloodstream infection 3, 5
• Use quantitative blood cultures: colony count from catheter hub ≥3-fold greater than peripheral vein confirms catheter-related bloodstream infection 3, 5

Multiple Organisms

• Detection of multiple enteric organisms in dialysate culture suggests possible intra-abdominal pathology requiring surgical evaluation 4
• New organism detected during treatment of initial peritonitis may indicate treatment failure and need for catheter removal 4

Common Pitfalls

• Do not rely on clinical findings alone for diagnosis—they have poor sensitivity and specificity 3
• Do not delay obtaining cultures before starting antibiotics, as this significantly reduces diagnostic yield 3
• Do not assume the catheter tunnel is uninvolved based on physical examination alone—ultrasound frequently reveals subclinical involvement 6
• Do not overlook fungal peritonitis in patients with risk factors (recent bacterial peritonitis, immunosuppression, contaminated equipment) 1, 2