Validation of a strategy for HCV antibody testing with two enzyme immunoassays in a routine clinical laboratory

BackgroundCenters for Disease Control (CDC) guidelines require confirmation of hepatitis C virus (HCV) screening-test-positive sera with a low signal/cut-off (S/CO) ratio by recombinant immunoblot or PCR. The UK Health Protection Agency has suggested that a second enzyme immunoassay (EIA) could be used as an alternative for confirmation in non-immunocompromised patients.ObjectiveTo evaluate the UK HPA approach in 17,936 consecutive in-house sera submitted for HCV testing.Study designAxSYM-positive sera (S/CO ≥ 1.0) were tested with Monolisa Plus. AxSYM-positive sera of patients that were confirmed PCR-positive were considered HCV+. All other AxSYM-positive sera were confirmed with immunoblot according to CDC guidelines.Results17,299 sera were negative with AxSYM. Of the 637 AxSYM-positive sera, 384 were from patients confirmed as PCR-positive. Of other 250 sera, 120 were negative with immunoblot, 103 were positive and 30 were indeterminate. All 30 immunoblot-indeterminate sera were PCR-negative. Two patients were Monolisa Plus+ and immunoblot− and PCR−. One patient was known as immunoblot−, while the other patient was diagnosed with non-A non-B hepatitis in 1980s. Nine sera from HCV-positive patients were Monolisa Plus−. Two PCR− sera were from immunocompetent patients who were PCR− for ≥8 years and six PCR− sera and one PCR+ serum were from immunocompromised patients. Sensitivity and specificity of confirmation with Monolisa Plus were 98.15% and 98.33% and the positive and negative predictive values were 99.58% and 92.91% in AxSYM-positive sera (excluding immunoblot-indeterminate/PCR-negative sera). If immunocompromised patients that were false-negative were excluded, sensitivity was 99.58%.ConclusionMonolisa Plus can be used as an alternative to immunoblot for the confirmation of AxSYM-positive sera.