What is the white blood cell (WBC) count indicative of spontaneous bacterial peritonitis (SBP)?

From the Guidelines

A white blood cell (WBC) count of ≥250 neutrophils/mm³ in ascitic fluid is diagnostic of spontaneous bacterial peritonitis (SBP). This threshold is the established criterion for diagnosis and initiation of treatment, as indicated by the most recent and highest quality study 1. When evaluating a patient with ascites, particularly those with cirrhosis who develop fever, abdominal pain, or altered mental status, a diagnostic paracentesis should be performed immediately. The fluid should be sent for cell count with differential, as well as culture in blood culture bottles to increase the yield of bacterial growth.

Key Points

• Treatment should be initiated promptly when the neutrophil count meets or exceeds this threshold, even before culture results are available, as supported by 1 and 1.
• This cutoff value has been determined based on studies showing that counts above this level correlate with bacterial infection of the ascitic fluid.
• The neutrophil count is more specific than the total WBC count because neutrophils are the primary cellular response to bacterial infection.
• Some clinicians use a total WBC count of ≥500 cells/mm³ with ≥50% neutrophils as an alternative diagnostic criterion, but the neutrophil count of ≥250/mm³ remains the gold standard, as noted in 1, 1, and 1.

Considerations

• The use of reagent strips for rapid diagnosis of SBP is not recommended due to low sensitivity and high false-negative rate, as stated in 1 and 1.
• Empirical antibiotic therapy should be started immediately after the diagnosis of SBP, with potentially nephrotoxic antibiotics avoided, as recommended in 1 and 1.
• The choice of antibiotic therapy should consider the severity of infection, local resistance profiles, and the environment of the infection, as discussed in 1.

From the Research

White Blood Cell Count for Spontaneous Bacterial Peritonitis (SBP)

• The diagnosis of SBP is established by a polymorphonuclear cell count in ascitic fluid ≥ 250 cells/mm^3 2, 3, 4, 5, 6
• A white blood cell (WBC) count of ≥ 250 cells/mm^3 in ascitic fluid is considered diagnostic of SBP 2, 3, 4, 5, 6
• The presence of fever and an elevated lactate dehydrogenase (LDH) level in ascitic fluid can also support the diagnosis of SBP 2, 3

Diagnostic Criteria for SBP

• Polymorphonuclear cell count in ascitic fluid ≥ 250 cells/mm^3 2, 3, 4, 5, 6
• Positive culture of ascitic fluid 2, 3, 4, 5, 6
• Elevated LDH level in ascitic fluid 2, 3
• Ascitic fluid protein level ≤ 1 gm/dl 2

Treatment and Prognosis of SBP

• Treatment with a third-generation cephalosporin achieves a cure rate in more than 80% of patients 5, 6
• Despite the improvement in short-term survival, the long-term prognosis of cirrhotic patients who survive an episode of SBP remains poor 4, 5, 6