Immediate diagnostic criteria for bacterial infection of ascitic fluid. Evaluation of ascitic fluid polymorphonuclear leukocyte count, pH, and lactate concentration, alone and in combination.

We prospectively evaluated the ascitic fluid (AF) polymorphonuclear cell (PMN) count, pH, and lactate concentration in single ascitic fluids from 60 patients to determine their relative predictive values for the immediate diagnosis of ascitic fluid infection. Nine of the 60 ascitic fluids were malignant. Of the remaining 51 samples, nine from cirrhotic patients were infected. The mean AF pH, lactate concentration, and PMN count in the infected group were 7.20 +/- 0.19, 80 +/- 51 mg/dl, and 18,199 +/- 19,650 cells/mm3, respectively, and all were significantly different from the corresponding values in noninfected ascites. Mean arterial blood-ascitic fluid (B-AF) pH and lactate gradients in the infected group were 0.23 +/- 0.17 and -46 +/- 31 mg/dl, respectively, and were significantly different from the corresponding values in noninfected ascites (p less than 0.05). Significant differences were not found between infected and malignant ascites, except for the AF PMN count (p less than 0.001). In cirrhosis with ascites, an AF pH less than or equal to 7.34 was the most specific single test (100%) and had the highest diagnostic accuracy (98%). In the larger group of patients with ascites of diverse etiology, a B-AF pH gradient greater than or equal to 0.10 or an AF PMN count greater than or equal to 500 cells/mm3 were the single tests with the highest diagnostic accuracy (92%). Combining an AF PMN count greater than 500 cells/mm3 with any of the other diagnostic criteria increased the specificity and diagnostic accuracy (up to 98%) compared to the best single criterion. Although our data support the use of a number of different combinations of AF measurements for the immediate diagnosis of infection, the simplest and most readily obtainable measurements are the pH and PMN count. Therefore, in the clinical setting we recommend the use of either an AF pH less than or equal to 7.34 or a B-AF pH gradient greater than or equal to 0.10 in combination with an AF PMN count greater than 500 cells/mm3 to obtain the highest degree of accuracy in the immediate diagnosis of ascitic fluid infection.