How to diagnose Spontaneous Bacterial Peritonitis (SBP)?

From the Guidelines

Spontaneous bacterial peritonitis (SBP) should be diagnosed through paracentesis, with a confirmed diagnosis when the ascitic fluid neutrophil count exceeds 250 cells/mm³, even without positive bacterial cultures, as recommended by the most recent guidelines 1. The procedure should be performed in patients with cirrhosis and ascites who present with fever, abdominal pain, altered mental status, or worsening liver/kidney function.

• Additional diagnostic tests include examining the ascitic fluid for glucose, protein, lactate dehydrogenase, and albumin levels, as well as sending samples for Gram stain and culture to identify the causative organism.
• The serum-ascites albumin gradient (SAAG) should be calculated to confirm the ascites is related to portal hypertension (SAAG ≥1.1 g/dL).
• Empiric antibiotic therapy, typically with a third-generation cephalosporin like ceftriaxone 1-2g IV daily, should be started immediately after obtaining fluid samples if SBP is suspected, without waiting for culture results, as supported by recent studies 1. SBP is a serious complication of cirrhosis with high mortality, so prompt diagnosis and treatment are essential to improve outcomes.
• The choice of antibiotic should be guided by local resistance patterns and the severity of infection, with consideration of the environment of the infection, whether community-acquired, health care-associated, or nosocomial 1.
• In areas with high prevalence of multi-drug resistant organisms (MDROs), alternative antibiotics such as piperacillin/tazobactam or meropenem may be considered 1.

From the Research

Diagnosis of Spontaneous Bacterial Peritonitis (SBP)

To diagnose SBP, the following steps can be taken:

• Perform a diagnostic paracentesis in all patients with ascites and clinical features with high diagnostic suspicion 2, 3, 4
• Analyze the ascites for the presence of > 250 mm3 neutrophil polymorphonuclear (PMN) in ascites, which is considered diagnostic for SBP 2, 4
• Culture the ascitic fluid to identify the infecting organism, with bedside injection of blood culture bottles being the recommended method 3, 5
• Evaluate the ascitic fluid for total protein, lactate dehydrogenase, and glucose levels to distinguish SBP from secondary peritonitis 3

Interpretation of Ascitic Fluid Analysis

The following parameters can be used to interpret the ascitic fluid analysis:

• Polymorphonuclear cell count: > 250 cells/mm3 is considered diagnostic for SBP 2, 4
• Ascitic fluid leukocyte count: > 1000 cells/microL increases the likelihood of SBP 5
• pH: < 7.35 increases the likelihood of SBP 5
• Blood-ascitic fluid pH gradient: > or = 0.10 increases the likelihood of SBP 5
• Serum-ascites albumin gradient: < 1.1 g/dL lowers the likelihood of portal hypertension 5

Risk Factors and Prevention

The following risk factors and prevention strategies should be considered:

• Patients with cirrhosis and ascites are at increased risk of developing SBP 2, 3, 6, 4
• Acid suppressive and beta-adrenergic antagonist therapies are strongly associated with SBP in at-risk individuals 6
• Prophylaxis should be limited to high-risk settings 3
• Liver transplant evaluation should be undertaken for patients who develop SBP barring contraindications 6