The diagnostic significance of hepatitis C virus antibody levels for chronic hepatitis C virus infection

Background/Aims: Although anti-hepatitis C virus (HCV) assay is widely used to screen for HCV infection, it has a high false-positive (FP) rate in low-risk populations. We investigated the accuracy of anti-HCV signal-to-cutoff (S/CO) ratio to dis-tinguish true-positive (TP) from FP HCV infection.Methods: We retrospectively analyzed 77,571 patients with anti-HCV results. A receiver operating characteristic (ROC) curve analysis was performed to evaluate the diagnostic accuracy of anti-HCV S/CO ratio in anti-HCV positive patients.Results: Overall, 1,126 patients tested anti-HCV positive; 34.7% of patients were FP based on HCV RNA and/or recombinant immunoblot assay (RIBA) results. The age and sex-adjusted anti-HCV prevalence was 1.22%. We identified significant differences in serum aspartate transaminase and alanine transaminase levels, anti-HCV S/CO ratio, and RIBA results between groups (viremia vs. non-viremia, TP vs. FP). Using ROC curves, the optimal cutoff values of anti-HCV S/CO ratio for HCV viremia and TP were 8 and 5, respectively. The area under the ROC curve, sensitivity, specificity, positive and negative predictive values were 0.970 (95% CI, 0.959-0.982, p < 0.001), 99.7%, 87.5%, 87.4%, and 99.7%, respectively, for predicting HCV viremia at an anti-HCV S/CO ratio of 8 and 0.987 (95% CI, 0.980-0.994, p < 0.001), 95.3%, 94.7%, 97.1%, and 91.4%, respectively, for TP HCV infection at an anti-HCV S/CO ratio of 5. No patients with HCV viremia had an anti-HCV S/CO ratio below 5. Conclusions: The anti-HCV S/CO ratio is highly accurate for discriminating TP from FP HCV infection and should be considered when diagnosing HCV infections.