Diagnostic accuracy of the multistix 8 SG reagent strip in diagnosis of spontaneous bacterial peritonitis

Recent studies have shown that the diagnosis of spontaneous bacterial peritonitis (SBP) can be rapidly obtained using leukocyte esterase reagent strips. However, published studies were restricted to one or two centers, and the number of patients with SBP was thus limited. The aims of the current prospective multicenter study were: (1) to assess the diagnostic accuracy of the Multistix 8SG urine test for the diagnosis of SBP; and (2) to assess the prevalence of SBP. From January to May 2004, 2 reactive strips were tested independently in inpatients with cirrhosis and in outpatients undergoing paracentesis. Cultures of ascitic fluid were performed at the bedside using aerobic and anaerobic blood culture bottles. Two thousand one hundred twenty-three paracenteses were performed in 1,041 patients from 70 centers. One hundred seventeen samples, obtained from 91 patients, had ascites polymorphonuclear cell (PMN) counts >= 250/mu l (range, 250-34,000), among which 56 were associated with positive ascitic fluid cultures. The prevalence of SBP was 5.5% in the whole population, 9% in inpatients, and 1.3% in outpatients (P < 0.0001). The prevalence of SBP was 0.57% in asymptomatic outpatients versus 2.4% in symptomatic outpatients (P = 0.04). Using a threshold of 2+ for positivity of the reagent strip, sensitivity was 45.3% for the diagnosis of SBP, specificity was 99.2%, positive predictive value was 77.9%, and negative predictive value was 96.9%. Conclusion: This study confirms the low prevalence of SBP in asymptomatic outpatients according to a priori defined criteria, and indicates an absence of diagnostic efficacy for this specific strip test.