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.
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