How to interpret borderline HCV antibody test results: a comparative study investigating four different anti-HCV assays.

Anti-HCV testing is the first step to diagnose hepatitis C. Although anti-HCV assay performance improved during the last 2 decades, very high sensitivity required for screening may lead to limitations in specificity. Thus, there remains an uncertainty how to interpret anti-HCV test results with a borderline signal-to-cut-off ratio. Comparison was made of concordance and performance of four licensed anti-HCV assays in samples with borderline signal-to-cut-off ratios. Out of 12,090 consecutive samples tested for anti-HCV with the Abbott Architect Anti-HCV assay over a period of 29 months, 95 plasma samples with a signal-to-cut-off ratio between 0.5 and 2 were selected for this study. All samples were re-tested with the Enzygnost Anti-HCV version 4.0, the Ortho anti-HCV version 3.0, and the Monolisa anti-HCV-Plus version 2 assays. Discordant samples were classified by additional immunoblot testing. Overall, only 52% of the Architect borderline samples gave similar results in all four assays. Inter-assay concordance ranged between 58% and 80%. The highest discordance was observed between the Architect and the Monolisa assay (42%). In contrast, a high level of concordance was found between the Enzygnost and Ortho assays (80%). The Monolisa was best to identify negative samples (100%), while the Enzygnost correctly classified most of the positive samples (96%). Anti-HCV antibody assays show significant variation in classifying samples with low signal-to-cut-off ratios. Different performances may have cost and management implications, as false-positive results are not infrequent. However, sensitivities were good for all assays if indeterminate results are not considered as negative.