USMLE Prep - Medical Reference Library

Spontaneous Bacterial Peritonitis — Diagnosis & Treatment

System: Hepatology • Reviewed: Aug 31, 2025 • Step 1Step 2Step 3

Synopsis:

In cirrhosis with ascites, diagnose when PMN count is 250 cells per mm3 or higher; start third generation cephalosporin and give IV albumin on days 1 and 3; begin prophylaxis after recovery.

Key Points

  • Stabilize ABCs; begin targeted evaluation without delaying life-saving therapy.
  • Use system-specific risk tools to guide testing and disposition.
  • Order high-yield tests first; escalate imaging when indicated.
  • Start evidence-based initial therapy and reassess frequently.

Algorithm

  1. Primary survey and vitals; IV access and monitors.
  2. Focused history/physical; identify red flags and likely etiologies.
  3. Order system-appropriate labs and imaging (see Investigations).
  4. Initiate guideline-based empiric therapy (see Pharmacology).
  5. Reassess response; arrange consultation and definitive management.

Clinical Synopsis & Reasoning

For Spontaneous Bacterial Peritonitis, frame the differential by acuity and pathophysiology, then align diagnostics to the leading hypotheses. Prioritize stabilization while obtaining high‑yield studies such as CBC (Baseline hematology), BMP (Electrolytes/renal). Incorporate bedside imaging and targeted labs to define severity and identify complications; synthesize results with clinical trajectory to refine the working diagnosis and disposition needs.


Treatment Strategy & Disposition

Initiate disease‑directed therapy alongside supportive care, titrating to objective response. Pharmacologic options commonly include Analgesia/Antipyretics. Use validated frameworks (e.g., Key Diagnostic Cutoffs) to guide escalation and site of care. Address precipitating factors, de‑escalate empiric therapies with data, and arrange follow‑up for monitoring and risk‑factor modification; admit patients with instability, high risk of deterioration, or needs for close monitoring.


Epidemiology / Risk Factors

  • Risk factors vary by condition and patient profile

Investigations

TestRole / RationaleTypical FindingsNotes
CBCBaseline hematologyAbnormal counts
BMPElectrolytes/renalDerangements

Key Diagnostic Cutoffs

ParameterThreshold
PMN count≥250 cells/mm3
CulturePositive or negative does not exclude diagnosis

Pharmacology

MedicationMechanismOnsetRole in TherapyLimitations
Cefotaxime/CeftriaxoneCephalosporinHoursFirst-line therapyAllergy
Albumin (IV)Volume expansionHoursPrevents HRS (selected)Fluid overload

Prognosis / Complications

  • Prognosis depends on severity, comorbidities, and timeliness of care

Patient Education / Counseling

  • Explain red flags and when to seek emergent care.
  • Reinforce medication adherence and follow-up plan.

Notes

Consider resistant organisms in nosocomial cases. Evaluate for secondary peritonitis if polymicrobial cultures, very high protein, or poor response.


References

  1. AASLD Practice Guidance — Ascites and SBP — Link
  2. EASL Clinical Practice Guidelines — Link