In a patient with cirrhosis and ascites who develops new fever, abdominal pain, worsening encephalopathy, or renal dysfunction, how should spontaneous bacterial peritonitis be diagnosed and managed?

Diagnosis of Spontaneous Bacterial Peritonitis

Perform diagnostic paracentesis immediately in any cirrhotic patient with ascites who develops fever, abdominal pain, worsening encephalopathy, or renal dysfunction—SBP is diagnosed when ascitic fluid polymorphonuclear (PMN) count exceeds 250 cells/mm³, and empiric antibiotics must be started immediately without waiting for culture results. 1, 2

When to Perform Diagnostic Paracentesis

All hospitalized cirrhotic patients with ascites require paracentesis upon admission, even without symptoms, because approximately 10% have SBP at presentation and up to one-third of SBP cases are completely asymptomatic. 3, 1, 2

Specific clinical triggers mandating urgent paracentesis include:

• Fever or systemic inflammatory signs (chills, tachycardia, tachypnea, hypothermia) 3, 1
• Abdominal pain or tenderness 3, 1
• Hepatic encephalopathy (new onset or worsening) 3, 1
• Renal dysfunction or worsening creatinine 3, 1
• Gastrointestinal bleeding (bacterial infection develops in 25-65% of these cases) 3, 1
• Hemodynamic instability or shock 1, 2
• Unexplained acidosis or peripheral leukocytosis 3

Essential Diagnostic Tests on Ascitic Fluid

Primary Diagnostic Criterion

The ascitic fluid PMN count >250 cells/mm³ is the gold-standard diagnostic criterion for SBP, regardless of culture results. 3, 1, 2 This threshold provides the greatest sensitivity, though a cutoff of 500/mm³ offers greater specificity. 3

Required Laboratory Tests

Obtain the following on every ascitic fluid sample:

• Cell count with differential (most critical initial test—can be performed in <4 hours) 3, 1
• Culture in bedside blood culture bottles (inoculate at least 10 mL to increase sensitivity to >90%) 1, 2
• Total protein concentration 3, 1
• Glucose and lactate dehydrogenase (LDH) to differentiate secondary peritonitis 3, 1
• Gram stain 1

Simultaneously obtain blood cultures before starting antibiotics to increase likelihood of isolating the causative organism. 1, 2

Technical Considerations

Manual microscopy with Giemsa staining is the traditional standard, though recent evidence suggests automated cell counters may be acceptable. 3 Reagent strips (leukocyte esterase) lack sufficient diagnostic accuracy and are not recommended for routine use. 3, 4

Differentiating Secondary from Spontaneous Peritonitis

Secondary peritonitis requires surgical intervention and has different antibiotic coverage needs. Suspect secondary peritonitis when:

• Multiple organisms on Gram stain or culture (SBP is characteristically monomicrobial) 1, 2, 5
• PMN count >1,000 cells/mm³ 1
• At least two of the following "Runyon criteria": ascitic total protein ≥1 g/dL, LDH above upper limit of normal for serum, glucose <50 mg/dL 3, 1
• Inadequate clinical response to appropriate antibiotics 3, 1
• Ascitic CEA >5 ng/mL or alkaline phosphatase >240 U/L (suggests intestinal perforation) 1

When secondary peritonitis is suspected, obtain abdominal CT scan immediately to identify perforation or abscess requiring surgery. 1

Immediate Management

Empiric Antibiotic Therapy

Start antibiotics immediately after paracentesis if PMN >250 cells/mm³, without awaiting culture results. 3, 1, 2 Each hour of delay increases mortality by 10% in septic shock and 3.3% overall. 2

First-line regimen for community-acquired SBP:

• Cefotaxime 2 g IV every 8-12 hours (77-98% resolution rate) 3, 1
• 5-day course is as effective as 10-day course 1

Alternative regimens with comparable efficacy:

• Amoxicillin-clavulanic acid (IV then oral) 1
• Ciprofloxacin (7 days IV or 2 days IV followed by 5 days oral) 1
• Oral ofloxacin 400 mg twice daily (for selected inpatients without prior quinolone exposure, vomiting, shock, or grade II+ encephalopathy) 3

For healthcare-associated or nosocomial SBP, use broader-spectrum coverage (piperacillin-tazobactam or carbapenem) due to rising multidrug resistance. 1, 4

Avoid aminoglycosides due to nephrotoxicity. 1

Albumin Administration

All patients with SBP should receive intravenous albumin in addition to antibiotics:

• 1.5 g/kg at diagnosis
• 1.0 g/kg on day 3 1, 4

This reduces hepatorenal syndrome from 30% to 10% and lowers 30-day mortality from 29% to 10%. 1 Greatest benefit occurs in patients with serum bilirubin ≥4 mg/dL and creatinine ≥1 mg/dL, though guidelines recommend albumin for all SBP cases. 1

Special Considerations

**Symptomatic patients with PMN <250 cells/mm³ but signs of infection** (fever >100°F, abdominal pain/tenderness) should receive empiric antibiotics while awaiting culture results. 3, 1

Culture-negative neutrocytic ascites (PMN >250 cells/mm³ with negative cultures) should be treated identically to culture-positive SBP, as clinical outcomes and mortality are similar. 2

Follow-Up

Repeat paracentesis at 48 hours is advised if clinical response is inadequate or if secondary peritonitis is suspected. 1 Most patients with typical SBP in the setting of advanced cirrhosis with dramatic clinical response do not require routine follow-up paracentesis. 3

Common Pitfalls

• Delaying paracentesis in asymptomatic patients—remember that one-third of SBP cases have no symptoms 1, 2
• Waiting for culture results before starting antibiotics—cultures are negative in up to 60% of cases 3, 5
• Using reagent strips as primary diagnostic tool—they lack adequate sensitivity and specificity 3
• Failing to give albumin—this significantly reduces mortality and should not be omitted 1, 4
• Inadequate antibiotic coverage for nosocomial SBP—these require broader-spectrum agents 1, 4