Sensitivity of diagnosis of spontaneous bacterial peritonitis is higher with the automated cell count method.

Background: Spontaneous bacterial peritonitis (SBP) is one of the most important complications of patients with liver cirrhosis entailing high morbidity and mortality. Making an accurate early diagnosis of this infection is key in the outcome of these patients. The current definition of SBP is based on studies performed more than 40 years ago using a manual technique to count the number of polymorphs in ascitic fluid (AF). There is a lack of data comparing the traditional cell count method with a current automated cell counter. Moreover, current international guidelines do not mention the type of cell count method to be employed and around half of the centers still rely on the traditional manual method.

Aim: To compare the accuracy of polymorph count on AF to diagnose SBP between the traditional manual cell count method and a modern automated cell counter against SBP cases fulfilling gold standard criteria: Positive AF culture and signs/symptoms of peritonitis.

Methods: Retrospective analysis including two cohorts: Cross-sectional (cohort 1) and case-control (cohort 2), of patients with decompensated cirrhosis and ascites. Both cell count methods were conducted simultaneously. Positive SBP cases had a pathogenic bacteria isolated on AF and signs/symptoms of peritonitis.

Results: A total of 137 cases with 5 positive-SBP, and 85 cases with 33 positive-SBP were included in cohort 1 and 2, respectively. Positive-SBP cases had worse liver function in both cohorts. The automated method showed higher sensitivity than the manual cell count: 80% vs 52%, P = 0.02, in cohort 2. Both methods showed very good specificity (> 95%). The best cutoff using the automated cell counter was polymorph ≥ 0.2 cells × 10⁹/L (equivalent to 200 cells/mm³) in AF as it has the higher sensitivity keeping a good specificity.

Conclusion: The automated cell count method should be preferred over the manual method to diagnose SBP because of its higher sensitivity. SBP definition, using the automated method, as polymorph cell count ≥ 0.2 cells × 10⁹/L in AF would need to be considered in patients admitted with decompensated cirrhosis.