Diagnostic problems in spontaneous bacterial peritonitis

In spontaneous bacterial peritonitis (SBP) the ascitic fluid culture (certain criterion of diagnosis) may be negative despite an evident clinical and biochemical picture. Therefore the diagnosis may be sometimes more "probable" than "certain". The authors performed a comparative analytical study--from a clinical, biochemical and prognostic point of view--between a group of 10 "probable" SBP (10 cirrhotic pts.) and 9 "certain" SBP (9 cirrhotic pts.). 115 "normal ascitic fluids" (negative culture in absence of any SBP-symptoms), collected from 82 cirrhotic pts., were used as control group. The ascitic concentration of white blood cells (WBC)/mmc and polymorphonuclear cells (PMN)/mmc was significantly different between the SBP and control group (p less than 0.001) and between the "certain" and "probable" SBP (p less than 0.02). The latter have a mean WBC and PMN/mmc count that is lower than the "certain" SBP and on the contrary a significantly higher ascitic glucose content (p less than 0.05). Probably that means a lower ascitic bacterial inoculum, which is below the threshold of detectability by current culture techniques. Serum laboratory tests showed no differences between the "probable" and the "certain" SBP groups, although, however they were worse than the control group. The symptoms and the prognosis resulted nearly the same in both groups. In spite of a high rate of recovery (57.9%) the global survival at the follow-up (10 +/- 5.2 months, range 6-19) was only 26.3%. The wide clinical, biochemical and prognostic overlap of the two groups leads us to consider as "certain" all the cases of "probable" SBP. Owing to the fact that only an early recognition and therapy are known to affect the prognosis significantly, the obvious conclusion is that in the SBP the suspicion is more important that the diagnostic certainty. Furthermore--in agreement with previous studies--the cutoff limit of 250 PMN/mmc has shown the best statistical diagnostic value for a rapid diagnosis (sensibility 100%, diagnostic accuracy 92.5%, negative predictive value 100%, likelihood ratio 1.9).