How is Spontaneous Bacterial Peritonitis (SBP) diagnosed in patients with low Serum-Ascites Albumin Gradient (SAAG) ascites?

Diagnosis of Spontaneous Bacterial Peritonitis in Low SAAG Ascites

Spontaneous bacterial peritonitis (SBP) can be diagnosed in low SAAG ascites using the same diagnostic criteria as in high SAAG ascites: an ascitic neutrophil count >250 cells/mm³ in the absence of an intra-abdominal surgically treatable source of infection. 1

Diagnostic Approach

Primary Diagnostic Criteria

• Ascitic fluid neutrophil count >250 cells/mm³ - This is the gold standard for diagnosis regardless of SAAG status 1, 2
• Absence of an intra-abdominal surgically treatable source of infection 1

Mandatory Diagnostic Testing

1. Diagnostic paracentesis - Must be performed without delay in all patients with ascites 1
2. Ascitic fluid analysis should include:
   • Neutrophil count (manual or automated) 1
   • Total protein concentration 1
   • Bedside inoculation of ascitic fluid into blood culture bottles (10 ml per bottle) 1, 3

Additional Tests for Low SAAG Ascites

When dealing with low SAAG ascites (<1.1 g/dL), additional tests should be considered based on clinical suspicion:

• Cytology - For suspected malignancy 1
• Adenosine deaminase - For suspected tuberculosis (levels <40 IU/mL exclude TB) 1
• Amylase - For suspected pancreatic ascites (typically >1000 IU/L) 1

Clinical Considerations in Low SAAG Ascites

Differentiating SBP from Secondary Peritonitis

This distinction is particularly important in low SAAG ascites:

Parameter	SBP	Secondary Peritonitis
Neutrophil count	>250/mm³	Often >1000/mm³
Culture	Typically monobacterial	Often polymicrobial
Protein	Usually <1 g/dL	Often >1 g/dL
Glucose	Usually normal	Often <50 mg/dL

Common Pitfalls and Caveats

1. Do not rely on clinical impression or fluid appearance - Studies show physician clinical suspicion has poor sensitivity (42%) for detecting SBP, and even clear-appearing fluid can harbor infection 4

2. Do not delay paracentesis - Each hour of delay in diagnostic paracentesis is associated with a 3.3% increase in mortality 1, 2

3. Do not wait for culture results - Treatment should be initiated based on neutrophil count, not culture results 1, 2

4. Do not exclude SBP based on atypical presentation - SBP can be asymptomatic or present with subtle symptoms, especially in low SAAG states 2, 5

5. Do not rely on preprocedure coagulation parameters - These are likely unnecessary prior to paracentesis 3

Management Algorithm for Suspected SBP in Low SAAG Ascites

1. Perform immediate diagnostic paracentesis in any patient with:

   • New-onset ascites
   • Worsening of existing ascites
   • Signs of infection (fever, abdominal pain)
   • Worsening liver or renal function
   • Gastrointestinal bleeding
   • Hepatic encephalopathy
   • Shock 1, 2

2. Analyze ascitic fluid:

   • Neutrophil count (>250 cells/mm³ indicates SBP)
   • Culture (bedside inoculation into blood culture bottles)
   • Total protein, albumin
   • Additional tests based on clinical suspicion 1

3. If neutrophil count >250 cells/mm³:

   • Initiate empiric antibiotic therapy immediately
   • Consider albumin administration (particularly in patients with renal dysfunction) 2

4. If bacterascites is found (positive culture but neutrophil count <250 cells/mm³):

   • For symptomatic patients: treat as SBP
   • For asymptomatic patients: repeat paracentesis when culture results return 2

5. Consider a second diagnostic paracentesis at 48 hours from the start of treatment to check treatment efficacy 1

By following this algorithm, clinicians can effectively diagnose and manage SBP in patients with low SAAG ascites, potentially reducing morbidity and mortality associated with delayed diagnosis and treatment.