Ascitic fluid pH in alcoholic cirrhosis: a reevaluation of its use in the diagnosis of spontaneous bacterial peritonitis.

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Abstract
An ascitic fluid pH less than or equal to 7.31 has been advanced as being the best index in the early diagnosis of spontaneous bacterial peritonitis in cirrhotic patients. In order to test the validity of this criteria, 55 patients with alcoholic cirrhosis and ascites were studied. In each patient, arterial blood and ascitic fluid samples were analysed for pH, PCO2, total CO2 and PO2, and the pH gradient between blood and ascites was calculated. White blood cell and polymorphonuclear cell counts were determined in ascitic fluid, and cultures of ascites were done under aerobic and anaerobic conditions. Twelve patients had a culture proven spontaneous bacterial peritonitis. Their mean ascitic fluid pH (+/- SD) was 7.38 +/- 0.09 (range 7.21-7.49) and differed significantly (p less than 0.05) from that found in patients without spontaneous bacterial peritonitis: 7.44 +/- 0.06 (range 7.34-7.6.3). A marked overlap was observed, however, between the two groups, and only three out of the 12 patients with spontaneous bacterial peritonitis had an ascitic fluid pH less than or equal to 7.31. The pH gradient was 0.10 +/- 0.08 (range -0.01 to +0.28) in the spontaneous bacterial peritonitis group, as compared with 0.02 +/- 0.04 (range -0.09 to +0.12) in the sterile group (p less than 0.01), but a marked overlap was also noted between the two groups. In the spontaneous bacterial peritonitis group, the polymorphonuclear count was 3588 +/- 3849/microliter (range 60-11 776) versus 41 +/- 138/microliter (range 0-813) in the sterile group (p less than 0.0001). All but one patient in the spontaneous bacterial peritonitis group and only two patients in the sterile group had over 250 polymorphonuclear/ microliter. Thus, in our experience, neither the ascitic fluid pH nor the pH gradient values accurately discriminated the individual patients with and without spontaneous bacterial peritonitis. A polymorphonuclear count less than 250/ microliter remained the best criteria for the diagnosis of spontaneous bacterial peritonitis in cirrhotic patients, before having the results of ascitic fluid cultures.