## **Core Concept**
Spontaneous bacterial peritonitis (SBP) is an infection of the ascitic fluid in the absence of any obvious source of infection, such as a surgical wound or fistula. It is a serious complication commonly seen in patients with cirrhosis and ascites. The diagnosis of SBP is primarily made based on the analysis of ascitic fluid.

## **Why the Correct Answer is Right**
The correct answer, **> 250 cells/mm^3**, is based on the standard diagnostic criterion for SBP. The diagnosis of SBP is confirmed when the ascitic fluid neutrophil count is greater than 250 cells/mm^3. This threshold is used because it has been shown to correlate well with the presence of bacterial peritonitis and the need for antibiotic treatment. A higher neutrophil count in the ascitic fluid indicates a more severe infection.

## **Why Each Wrong Option is Incorrect**
- **Option A: 500 cells/mm^3**: While a neutrophil count of > 500 cells/mm^3 would certainly support the diagnosis of SBP, it is not the threshold used for the diagnosis. A count above 250 cells/mm^3 is sufficient.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that SBP should be suspected in any cirrhotic patient with ascites who presents with abdominal pain, fever, or signs of sepsis. Prompt diagnostic paracentesis (ascitic fluid analysis) is crucial. The ascitic fluid analysis should include cell count with differential, Gram stain, and culture. Patients with SBP require prompt antibiotic treatment.

## **Correct Answer:** . **> 250 cells/mm^3**