Runyon Criteria for Distinguishing Secondary from Spontaneous Bacterial Peritonitis
The Runyon criteria identify secondary bacterial peritonitis (requiring surgical intervention) when at least two of the following three ascitic fluid findings are present: total protein >1 g/dL, lactate dehydrogenase (LDH) greater than the upper limit of normal for serum, and glucose <50 mg/dL. 1
Diagnostic Algorithm
Initial Ascitic Fluid Analysis
When a cirrhotic patient presents with neutrocytic ascites (PMN ≥250 cells/mm³), order the following tests immediately: 1
- Gram stain and culture (inoculate into blood culture bottles at bedside)
- Total protein
- LDH
- Glucose
- Cell count with differential
Applying Runyon Criteria
For Free Perforation (100% sensitivity, 45% specificity): 1, 2
The presence of at least 2 of 3 criteria suggests gut perforation:
- Ascitic fluid total protein >1 g/dL
- Ascitic fluid LDH greater than upper limit of normal for serum
- Ascitic fluid glucose <50 mg/dL
Additional Supporting Features for Secondary Peritonitis
Beyond the classic Runyon criteria, suspect secondary bacterial peritonitis when: 1
- PMN count >1,000/mm³ (often many thousands)
- Multiple organisms on Gram stain or culture (frequently including fungi, enterococcus, or anaerobes)
- Ascitic fluid CEA >5 ng/mL (92% sensitivity, 88% specificity for gut perforation) 1
- Ascitic fluid alkaline phosphatase >240 U/L (92% sensitivity, 88% specificity for gut perforation) 1
- Failure of PMN count to decrease after 48 hours of appropriate antibiotic therapy 1
Critical Limitations and Clinical Context
Sensitivity Issues
The Runyon criteria (protein/LDH/glucose) are only 50% sensitive for detecting non-perforation secondary peritonitis (such as loculated abscesses without free perforation). 1 In a retrospective study, Runyon's criteria alone had 66.6% sensitivity for all secondary peritonitis. 3
When to Proceed with Imaging
Any patient meeting Runyon criteria or showing polymicrobial growth should undergo emergent abdominal CT scanning to identify surgically treatable sources. 1 CT was diagnostic in 85% of secondary peritonitis cases confirmed by surgery or autopsy. 3
Response to Treatment as Diagnostic Tool
In spontaneous bacterial peritonitis, the ascitic fluid PMN count decreases below baseline after 48 hours of antibiotic therapy; in secondary peritonitis, the PMN count rises or fails to decrease despite treatment. 1, 2 This response pattern has 100% sensitivity for distinguishing SBP from secondary peritonitis when assessed at 48 hours. 2
Clinical Pitfalls
Do not rely on clinical symptoms alone – signs and symptoms cannot reliably separate patients needing surgical intervention from those with SBP requiring only antibiotics. 1
Maintain high suspicion with localized abdominal findings – patients with localized abdominal pain, very high neutrophil counts, or inadequate response to therapy warrant aggressive investigation for secondary peritonitis. 1, 3
Mortality implications – secondary bacterial peritonitis carries 50-80% mortality versus 26-29% for SBP, making prompt differentiation critical. 1, 3 Early surgical evaluation (within 3.2 days of diagnostic paracentesis) showed trends toward improved survival compared to delayed intervention (7.2 days). 3
Management Based on Findings
If Runyon criteria positive or polymicrobial culture: 1
- Add anaerobic antibiotic coverage to third-generation cephalosporin
- Obtain emergent plain films, water-soluble contrast studies, and/or CT scanning
- Arrange immediate surgical consultation
- Proceed to laparotomy if perforation or abscess confirmed
If criteria negative and monomicrobial culture: 1
- Treat as SBP with cefotaxime 2g IV every 8 hours or ceftriaxone 1-2g IV every 12-24 hours
- Repeat paracentesis at 48 hours to confirm decreasing PMN count
- If PMN count fails to decrease, reconsider secondary peritonitis diagnosis