Spontaneous vs secondary bacterial peritonitis. Differentiation by response of ascitic fluid neutrophil count to antimicrobial therapy.

A retrospective chart review revealed 24 patients who had at least one subsequent ascitic fluid neutrophil count within 14 days of the ascitic fluid analysis that was diagnostic of spontaneous bacterial peritonitis. The neutrophil count decreased (after antibiotic therapy was started) at an exponential rate, with a half-life of 34 +/- 35 hours. In none of four episodes of secondary bacterial peritonitis was there an exponential decline in neutrophil count after antimicrobial therapy was initiated. In fact, the first follow-up neutrophil count was greater than the baseline value in all four episodes. The response pattern of the ascitic fluid neutrophil count to antimicrobial therapy is helpful in differentiating spontaneous from secondary bacterial peritonitis.