What peritoneal white blood cell (WBC) level indicates spontaneous bacterial peritonitis (SBP) in patients with cirrhosis and ascites?

Peritoneal WBC Level for Spontaneous Bacterial Peritonitis Diagnosis

The diagnosis of spontaneous bacterial peritonitis (SBP) is confirmed when the ascitic fluid neutrophil count exceeds 250 cells/mm³ in the absence of an intra-abdominal surgically treatable source of infection. 1

Diagnostic Criteria for SBP

Primary Diagnostic Threshold

• Neutrophil count >250 cells/mm³ in ascitic fluid is the established diagnostic threshold with optimal sensitivity 1
• This threshold has been validated in multiple studies and is recommended by both EASL and UK guidelines

Alternative Diagnostic Criteria

• PMN ≥500 cells/mm³ offers greater specificity but may miss some cases 1
• Total WBC >1000 cells/μL can also be used as a diagnostic marker 1

Diagnostic Accuracy

According to a meta-analysis of 14 prospective trials 1:

• PMN >250 cells/μL: Positive likelihood ratio of 6.4 (95% CI 4.6 to 8.8)
• PMN ≥500 cells/μL: Positive likelihood ratio of 10.6 (95% CI 6.1 to 18.3)
• WBC >1000 cells/μL: Positive likelihood ratio of 9.1 (95% CI 5.5 to 15.1)
• WBC >500 cells/μL: Positive likelihood ratio of 5.9 (95% CI 2.3 to 15.5)

Clinical Variants of SBP

1. Classical SBP: Positive culture with PMN >250 cells/mm³

2. Culture-negative neutrocytic ascites (CNNA): Negative culture with PMN >250 cells/mm³

   • Should be treated identically to culture-positive SBP 1
   • Represents the majority of SBP cases as cultures are frequently negative

3. Bacterascites: Positive culture with PMN <250 cells/mm³

   • Requires clinical assessment:
     • If symptomatic or signs of infection: Treat with antibiotics 1
     • If asymptomatic: Repeat paracentesis when culture results return; treat if PMN rises to >250/mm³ 1

Important Clinical Considerations

When to Perform Diagnostic Paracentesis

Paracentesis should be performed in patients with cirrhosis and ascites in the following scenarios 1:

• At hospital admission
• With fever or other signs of systemic inflammation
• With abdominal pain
• With gastrointestinal bleeding
• With worsening liver or renal function
• With hepatic encephalopathy

Pitfalls to Avoid

• Delayed diagnosis: Each hour of delay in diagnostic paracentesis increases in-hospital mortality by 3.3% 1
• Relying on symptoms alone: Up to 16% of SBP cases can be completely asymptomatic 2
• Waiting for culture results: Treatment should begin immediately after diagnosis based on cell count, without waiting for culture results 1
• Confusing with secondary bacterial peritonitis: Secondary peritonitis should be suspected with localized abdominal symptoms, multiple organisms on culture, very high neutrophil count, or inadequate response to therapy 1

Prognostic Indicators

Poor prognostic indicators in SBP include 3:

• Low ascitic protein
• Hepatic encephalopathy
• Coagulopathy
• Renal dysfunction (creatinine >2 mg/dl)
• Leukocytosis

Treatment Approach

• Start empirical antibiotic therapy immediately after diagnosis 1
• Third-generation cephalosporins (e.g., cefotaxime) are the first-line treatment 1, 4
• Consider albumin infusions to prevent hepatorenal syndrome 1
• Patients who recover from SBP should be evaluated for liver transplantation 1

The early diagnosis and prompt treatment of SBP using the established threshold of >250 neutrophils/mm³ has reduced mortality from >90% historically to approximately 20% in current practice 1.