The rapid determination of ascitic fluid L-lactate for the diagnosis of spontaneous bacterial peritonitis.

We have prospectively studied the value of ascitic fluid lactic acid levels by a rapid kit method in the diagnosis of SBP. Forty-five nonconsecutive patients admitted with ascites were investigated and their ascitic fluid cell counts and clinical presentation compared with ascitic fluid lactic acid levels. There were seven patients with SBP, six of whom had positive cultures. PMN were greater than 250/mm3 in 6/7 and lactic acid levels greater than 33 mg/dl in 7/7. In eight patients with malignancy without evidence of infection PMN was greater than 250/mm3 in 8/8 and lactic acid greater than 33 mg/dl in 1/8. In the 30 patients (31 samples) with cirrhotic ascites without SBP, 5/31 had elevated PMN and none had elevated lactic acid levels. From this small number of patients, the predictive value of PMN greater than 250/mm3 is 32% compared to 88% for lactic acid levels (if patients with malignancy are included). The predictive value of a PMN less than 250/mm3 is 96% and of lactic acid less than 33 mg/dl is 100%. Our study confirms that of Brook et al. (5), which used the same method and when the lactic acid results of both studies are combined, the sensitivity of lactic acid in SBP is 100% (15/15), the specificity is 96% (79/82), the predictive value positive is 83% (15/18), and the predictive value negative is 100% (76/76). We conclude that lactic acid levels above 33 mg/dl are more reliable than a PMN above 250/mm3 but that PMN and lactic acid levels below these values both accurately predict the absence of SBP. Lactic acid levels can be determined within 15 min and with minimal cost (presently $1.45/test) by a readily available kit as well as by automated equipment.