pH of ascitic fluid: diagnostic and prognostic value in cirrhotic and noncirrhotic patients.

The pH measurements of 185 samples of ascitic fluid in 169 cirrhotic and 16 noncirrhotic patients were analyzed to assess their diagnostic and prognostic value. The 169 cirrhotic patients were divided into four groups: sterile ascites (group 1), spontaneous bacterial peritonitis (group 2), probable spontaneous bacterial peritonitis (group 3), and bacterascites (group 4). Mean ascitic fluid pH values were lower (p less than 0.001) in patients of groups 2 (7.24 +/- 0.17) and 3 (7.34 +/- 0.11) than in patients of groups 1 (7.44 +/- 0.06) and 4 (7.45 +/- 0.08), but there was an important overlap between these groups. Mean arterial-ascitic fluid pH gradient values were higher (p less than 0.001) in patients of groups 2 (0.21 +/- 0.16) and 3 (0.10 +/- 0.13) than in patients of groups 1 (0.02 +/- 0.05) and 4 (0.02 +/- 0.05). This gradient had a better discriminant power than ascitic fluid pH alone. Sensitivity, specificity, positive and negative predictive value, and diagnostic accuracy for the diagnosis of certain or probable spontaneous bacterial peritonitis were, respectively, 47%, 99%, 88%, 89%, and 89% for ascitic fluid pH values less than 7.32; 66%, 99%, 91%, 93%, and 92% for arterial-ascitic fluid pH gradient values greater than 0.10; and 97%, 96%, 86%, 99%, and 96% for polymorphonuclear cell count greater than 75/microliter. Ascitic fluid pH values appeared to have a high prognostic value, as 6 of 7 cirrhotic patients with ascitic fluid pH values less than 7.15 died rapidly. Low ascitic fluid pH values were found in patients with malignant and pancreatic ascites and tuberculous peritonitis but not in patients with cardiac ascites. We conclude that in cirrhotic patients with certain or probable spontaneous bacterial peritonitis (a) arterial-ascitic fluid pH gradient measurements had a slightly higher diagnostic value than ascitic fluid pH measurements but a slightly lower diagnostic value than polymorphonuclear cell count and (b) ascitic fluid pH measurements had a high prognostic value. In noncirrhotic patients, ascitic fluid pH and arterial-ascitic fluid pH gradient measurements had a poor diagnostic value.