A 48-year-old woman with decompensated cirrhosis (Child-Pugh C) presents with fever (38.5°C), abdominal pain, and ascites. Diagnostic paracentesis shows ascitic fluid protein 1.2 g/dL, WBC 450/µL (85% neutrophils), glucose 40 mg/dL, and negative bacterial culture. What is the most likely diagnosis and the immediate next step in management?

Explanation

## Spontaneous Bacterial Peritonitis (SBP) in Cirrhosis ### Clinical Diagnosis This patient meets **diagnostic criteria for SBP** despite negative culture — a common scenario in cirrhosis. ### Diagnostic Criteria for SBP ```mermaid flowchart TD A[Cirrhotic patient with ascites + fever/abdominal pain]:::outcome --> B[Diagnostic paracentesis]:::action B --> C{Ascitic fluid PMN ≥ 250/µL?}:::decision C -->|Yes| D[SBP diagnosed]:::outcome C -->|No| E[Exclude other causes]:::action D --> F{Culture positive?}:::decision F -->|Yes| G[Culture-positive SBP]:::outcome F -->|No| H[Culture-negative SBP]:::outcome H --> I[Still treat as SBP]:::action ``` **Key Point:** SBP is diagnosed by **ascitic fluid PMN (polymorphonuclear neutrophil) count ≥ 250/µL**, NOT by positive culture. Culture is positive in only 40–50% of cases. ### Diagnostic Features in This Case | Parameter | Finding | Interpretation | |---|---|---| | **PMN count** | 450/µL (85% neutrophils) | **≥ 250/µL → SBP** | | **Protein** | 1.2 g/dL | Low protein (< 1.5 g/dL) = high SBP risk | | **Glucose** | 40 mg/dL | Low glucose suggests bacterial infection | | **Culture** | Negative | Culture-negative SBP (40–50% of cases); still treat | **High-Yield:** **Culture-negative SBP** is common and must be treated empirically based on PMN count — do NOT wait for culture results [cite:Harrison 21e Ch 307]. ### Immediate Management 1. **Start antibiotics immediately** (do not wait for culture): - **Ceftriaxone 1 g IV 12-hourly** (or cefotaxime 2 g IV 8-hourly) — covers gram-negative and gram-positive organisms. - Alternative: Fluoroquinolone (ofloxacin 400 mg BD) if allergy. 2. **Albumin supplementation:** - 1.5 g/kg on day 1, then 1 g/kg on day 3 (reduces renal failure and mortality). 3. **Supportive care:** - Fluid resuscitation, correction of coagulopathy. - Repeat paracentesis at 48 hours if no clinical improvement. 4. **Secondary prophylaxis:** - Norfloxacin 400 mg daily (or trimethoprim-sulfamethoxazole) to prevent recurrence. **Clinical Pearl:** SBP mortality is 20–40% even with treatment; albumin reduces mortality by ~10% — always give it. ### Why NOT Secondary Peritonitis? Secondary bacterial peritonitis (from perforation) shows: - **Higher protein** (> 1 g/dL, often > 2.5 g/dL). - **Multiple organisms** on culture (gram-positive + gram-negative + anaerobes). - **Imaging findings:** Free air, bowel perforation, loculated fluid. - This patient has low protein and **monomicrobial infection** (culture-negative, but PMN pattern suggests single organism) → **SBP**, not secondary peritonitis. ### Why NOT TB or Fungal? - **TB peritonitis:** Ascitic protein typically **> 2.5 g/dL**, lymphocytic predominance (not PMN), slow clinical course, positive TB culture/PCR. - **Fungal peritonitis:** Rare in non-immunocompromised; requires positive fungal culture; no acute PMN elevation. This patient's **acute presentation, PMN-dominant fluid, and low protein** are classic for **SBP**, not chronic infections.