Low C3 in cirrhotic ascites predisposes to spontaneous bacterial peritonitis

The risk of developing spontaneous bacterial peritonitis (SBP) in relation to the concentration of C3 in ascitic fluid (AF) has been studied prospectively in 33 patients with cirrhosis of the liver, seven of whom had one or more episodes of SBP during hospitalization. C3 concentrations in the AF of patients who developed infection (9.0 +/- 2.67 mg/dl) were significantly lower than in those who did not (18.26 +/- 8.11 mg/dl) (P less than 0.01). C4 concentrations were similar in both groups. A direct correlation was found between AF C3 and total protein concentrations (P less than 0.001). We conclude that a low C3 concentration in AF may predispose to SBP.