What are the diagnostic criteria and treatment options for a patient with suspected Spontaneous Bacterial Peritonitis (SBP)?

Spontaneous Bacterial Peritonitis (SBP): Diagnostic Criteria and Treatment

Diagnostic Criteria

SBP is diagnosed when ascitic fluid polymorphonuclear (PMN) leukocyte count exceeds 250 cells/mm³, regardless of culture results. 1, 2

When to Perform Diagnostic Paracentesis

• Perform diagnostic paracentesis immediately in ALL hospitalized cirrhotic patients with ascites at admission, even without symptoms 1, 3
• Urgent paracentesis is mandatory in patients presenting with: 1, 3
  • Fever or signs of systemic inflammation
  • Abdominal pain or gastrointestinal symptoms
  • Gastrointestinal bleeding or shock
  • Hepatic encephalopathy
  • Worsening liver or renal function

Critical pitfall: Up to 16% of SBP cases are completely asymptomatic, making routine screening paracentesis essential 1

Laboratory Diagnosis

• The diagnostic threshold is PMN count >250 cells/mm³ - this lower threshold is deliberately chosen because the mortality risk of missing SBP far outweighs the risk of overdiagnosis 1
• Inoculate at least 10 mL of ascitic fluid into aerobic and anaerobic blood culture bottles at bedside before starting antibiotics to achieve >90% culture sensitivity 1, 3
• Obtain blood cultures simultaneously before antibiotic initiation 1, 2
• Do NOT wait for culture results to initiate treatment - the PMN count alone is sufficient 1, 2

Special Diagnostic Scenarios

• Culture-negative neutrocytic ascites (PMN >250/mm³ with negative culture): Treat identically to culture-positive SBP with the same morbidity and mortality 1
• Bacterascites (positive culture but PMN <250/mm³): 1, 4
  • If symptomatic: Treat as SBP
  • If asymptomatic: Repeat paracentesis urgently, as 38% progress to frank SBP within hours
  • 62% resolve spontaneously without treatment

Treatment Protocol

Immediate Antibiotic Therapy

Initiate empirical antibiotics immediately upon diagnosis without waiting for culture results. 1, 2

First-line treatment for community-acquired SBP: 1, 2, 3

• Cefotaxime 2g IV every 8-12 hours for 5 days (77-98% resolution rate)
• Alternative: Ceftriaxone (third-generation cephalosporin)
• A 5-day course is as effective as 10 days 1, 2

Alternative for uncomplicated SBP in select patients: 1

• Oral ofloxacin 400mg twice daily
• Oral ciprofloxacin (for uncomplicated cases)

Nosocomial or healthcare-associated SBP: 3, 5

• Use broad-spectrum coverage: carbapenem or piperacillin-tazobactam
• Base selection on local resistance patterns

Critical antibiotic selection pitfalls: 1

• Never use quinolones in patients already on quinolone prophylaxis, in areas with high quinolone resistance, or in nosocomial SBP
• For patients developing SBP while on quinolone prophylaxis, use cefotaxime or amoxicillin-clavulanic acid

Albumin Therapy (Essential Component)

Administer IV albumin 1.5 g/kg body weight within 6 hours of diagnosis, followed by 1.0 g/kg on day 3. 1, 2, 3

• This regimen reduces mortality from 29% to 10% and decreases type 1 hepatorenal syndrome from 30% to 10% 1
• Particularly critical in patients with creatinine ≥1.0 mg/dL or bilirubin ≥5 mg/dL 3

Monitoring Treatment Response

48-Hour Follow-Up Paracentesis

Perform repeat diagnostic paracentesis at 48 hours after initiating antibiotics to assess treatment efficacy. 1, 2, 3

Treatment success criteria: 1, 2

• Ascitic PMN count decreases to <25% of pre-treatment value
• Clinical improvement accompanies laboratory response

Treatment failure definition: 1, 2

• PMN count fails to decrease by at least 25% from baseline
• Worsening clinical signs and symptoms

Management of Treatment Failure

If treatment fails at 48 hours: 1, 2, 3

• Broaden antibiotic coverage based on culture sensitivities or empirically escalate to broader-spectrum agents
• Obtain CT imaging to exclude secondary bacterial peritonitis (requires surgical evaluation)
• Consider resistant bacteria, particularly multidrug-resistant organisms 6, 5

Prognosis and Time-Sensitive Nature

• SBP carries approximately 20% hospital mortality despite infection resolution 1, 2
• Each hour of delay in antibiotic initiation increases mortality by 3.3-10% in cirrhotic patients with septic shock 1
• Early appropriate antibiotic treatment combined with albumin therapy significantly improves survival 1, 2