Is there yet any place for reagent strips in diagnosing spontaneous bacterial peritonitis in cirrhotic patients? An accuracy and cost-effectiveness study in Brazil

Abstract

Background: Diagnosis of spontaneous bacterial peritonitis (SBP) is currently based on ascitic cell counting, but there is a need for a more simple and rapid diagnostic tool. The objectives of this study are to evaluate the accuracy of reagent strips in diagnosing SBP and compare their costs with total and differential cell counts.

Patients and methods: 71 cirrhotic in- and outpatients were consecutively included (159 samples). Spontaneous bacterial peritonitis was defined as neutrophil cells >or= 250/microL. The cutoff values for each reagent strip were defined by a receiver operating characteristic (ROC) curve. Sensitivity (S), Specificity (Sp), Positive and Negative Predictive Values (PPV and NPV), Accuracy (Ac) and cost-effectiveness (US$) in comparison to cell count exam were calculated.

Results: Spontaneous bacterial peritonitis was diagnosed in 17 patients (23.9%), 11 of them with positive culture (64.7%). The best cutoff points found in ROC curves were 1+ for Multistix 10 SG and ca. 75 for Choiceline 10 (Multistix 10 SG S = 80%, Sp = 98.5%, PPV = 90.9%, NPV = 96.2%, Ac = 95%; Choiceline 10 S = 76.9%, Sp = 97.7%, PPV = 87%, NPV = 95.6%, Ac = 94%). In terms of cost-effectiveness by cost/accuracy, cell count was 41.5, Multistix 10 SG 0.57, and Choiceline 10, 0.19 (P < 0.001).

Conclusion: Reagent strips are a useful tool for diagnosing SBP in cirrhotic patients, but they have some limitations. Strips are especially indicated when total and differential cell counts are not quickly available or sometimes unavailable. They are also indicated as screening test in emergency rooms to anticipate the diagnosis of SBP and allow its early treatment. It's an interesting option in developing countries.