Sensitivity of a bedside reagent strip for the detection of spontaneous bacterial peritonitis in ED patients with ascites

Study objective: To determine the sensitivity of a highly sensitive bedside leukocyte esterase reagent strip (RS) for detection of spontaneous bacterial peritonitis (SBP) in emergency department (ED) ascites patients undergoing paracentesis. Methods: We conducted a prospective, observational cohort study of ED ascites patients undergoing paracentesis at two academic facilities. Two practitioners, blinded to each other's results, did a bedside RS analysis of the peritoneal fluid in each patient and documented the RS reading at 3-min according to manufacturer-specified colorimetric strip reading as either “negative”, “trace”, “small”, or “large”. The primary outcome measure was sensitivity of the RS strip for SBP (absolute neutrophil count ≥ 250 cells/mm³) at the “trace” threshold (positive equals trace or greater). Results: There were 330 cases enrolled, with 635 fluid analyses performed. Of these, 40 fluid samples had SBP (6%). Bedside RS had a sensitivity, specificity, positive predictive value, and negative predictive value of 95% (95% CI 82%–99%), 48% (95% CI 44%–52%), 11% (95% CI 10%–11%), and 99% (95% CI 97%–99%) respectively at the “trace” threshold for the detection of SBP. Conclusion: Bedside use of the RS in ED ascites patients demonstrated high sensitivity for SBP. Given the wide confidence intervals, we cannot currently recommend it as a stand-alone test. We recommend further study with a larger number of SBP patients, potentially combining a negative RS result with low clinical suspicion to effectively rule out SBP without formal laboratory analysis.