Research ArticleA new highly sensitive point of care screen for spontaneous bacterial peritonitis using the leukocyte esterase method

Background & AimsUrine reagent strips measuring leukocyte esterase activity have been studied to screen spontaneous bacterial peritonitis (SBP) but are insensitive. We calibrated a strip specifically for ascitic fluid to achieve high sensitivity in this diagnosis.MethodsExperiments were conducted on ascitic fluid from patients with cirrhosis. Samples with SBP were diluted with native acellular ascitic fluid to achieve PMN counts below, above, and close to the diagnostic threshold of 250 PMN/μl. A model of SBP was created by spiking negative ascitic fluid samples (<250 PMN/μl) with activated PMN from blood of patients with sepsis, and diluted to achieve a range of PMN. Aliquots were tested at 2, 3, 4, and 10 min with the Periscreen™ leukocyte esterase strip. PMN/μl was correlated to timings and color scales: white defined negative (PMN <250/μl); and shades of brown, purple, and pink defined positive. Ascitic fluid samples were obtained from 58 patients. Negative ascitic fluid was used from 32 to generate the model SBP.ResultsOne thousand three hundred and four experiments were performed with a median PMN count of 492/μl (0-7510). After exclusion of uninterpretable colorimetric results, 1089 experiments were analyzed [PMN of 444/μl (0-7510)]. The best result was obtained at 3 min (n = 299), with Se: 100%, Sp: 57.9%; NPV: 100%, PPV: 76.5%. The test was not interpretable in bloody, chylous or bilious ascitic fluid, or concurrent imipenem treatment.ConclusionsThis new leukocyte esterase strip calibrated to an ascitic fluid PMN count ⩾250/μl is a robust screening tool when the strip turns any hue of tan/brown at 3 min.