Evaluation of HCV RNA by PCR and Signal-to-Cutoff Ratios of HCV Antibody Assays for Diagnosis of HCV Infection

Myeong Hee Kim, MD; So Young Kang, MD; Woo In Lee, MD; Min Young Lee, MD


Lab Med. 2021;52(3):240-244. 

In This Article

Abstract and Introduction


Objective: In this study, we assessed whether a hepatitis C virus (HCV) RNA test could replace recombinant immunoblot assay (RIBA) and reduce unnecessary supplemental tests as the signal-to-cutoff (S/Co) ratio from anti-HCV antibody (Ab) tests.

Methods: Anti-HCV Ab tests were performed to screen for HCV infections, and RIBA and real-time polymerase chain reaction were performed for HCV RNA to confirm HCV infection. Receiver operating characteristic curves were evaluated to determine the optimal S/Co ratios for predicting HCV infection.

Results: The cutoff value for the S/Co ratio was 3.63 for predicting RIBA results and 10.6 for predicting HCV RNA results. Our data suggested that an S/Co ratio ≥10.6 indicated a high risk of active HCV infection. An S/Co ratio of 3.63 to 10.6 needed further evaluation and repeat HCV RNA testing. No further testing was required for S/Co ratios <3.63 or ≥10.6.

Conclusion: We determined that the S/Co ratio of the anti-HCV Ab test provides useful information to confirm HCV infections, including the need for further laboratory testing or clinical follow-up.


Hepatitis C virus (HCV) is a major cause of chronic liver disease globally and associated morbidity and mortality.[1] Laboratory testing is important in diagnosis and follow-up of patients with HCV infections. The methods for diagnosing HCV infection are detecting circulating antibodies (Abs) against HCV and detecting HCV RNA.[2] The traditional approach to HCV testing is initial screening for anti-HCV Ab followed by supplementary testing using a recombinant immunoblot assay (RIBA), because of the chance of false positives from anti-HCV Ab tests. Physicians use HCV RNA tests to monitor responses to treatment and sometimes to confirm anti-HCV Ab positivity. However, the strategy for diagnosing HCV infection changed after discontinuation of the RIBA reagent in the United States. In 2013, the Centers for Disease Control and Prevention (CDC) updated its guidelines for testing for HCV infections, recommending that a reactive result for an anti-HCV Ab test should be followed by an HCV RNA test.[3] Meanwhile, the CDC stated that more studies are needed for a strategy to confirm a diagnosis of HCV infection.[3] Therefore, patients with negative HCV RNA tests are required to have confirmation by further evaluation. Several studies have suggested that RIBA can be substituted with the signal-to-cutoff (S/Co) ratio of the anti-HCV Ab concentration.[4] In this study, we analyzed whether HCV infection could be diagnosed correctly with an anti-HCV Ab test and an HCV RNA test without RIBA and evaluated the diagnostic performance with and without RIBA and the usefulness of the S/Co ratio.