We studied the usefulness of the recently designed Trak-C assay for the detection and quantification of the hepatitis C virus (HCV) core antigen (Ag) for the screening of HCV infection in 4,201 subjects selected from 74,150 consecutive volunteers undergoing routine medical checkups. Subjects were selected for screening because they had risk factors (group II, n ‫؍‬ 321) and/or elevated alanine transaminase activity (group I, n ‫؍‬ 3847). Initially, the anti-HCV antibody assay and the Trak-C assay were performed on each patient. Subsequently, the Trak-C assay was performed only when the anti-HCV enzyme immune assay (EIA) was positive. Positive samples were further evaluated for anti-HCV antibodies by a third-generation strip immunoblot assay and for HCV RNA. Four samples (1.2%) from group II and 113 (2.9%) from group I were anti-HCV EIA positive. We also tested 33 subjects who previously tested positive for anti-HCV in our medical center. Among the 150 anti-HCV EIA-positive samples, the HCV core Ag result was in accord with the HCV RNA result in 146 cases (97.3%). When the EIA result was positive, the HCV core Ag concentration and the HCV RNA load were correlated (r 2 ‫؍‬ 0.78; P < 0.001). Four samples with low viral loads were Trak-C negative but HCV RNA positive. Among the 2,395 anti-HCV EIA-negative serum samples collected during the first part of the study, 17 (0.7%) were found to contain very low levels of HCV core Ag (<8.5 pg/ml, the cutoff value being 1.5 pg/ml). All these samples were HCV RNA negative and considered to be false positives. This was confirmed by HCV core Ag neutralization analysis. The HCV core Ag assay is a useful method in the screening strategy of HCV infection and provides a reliable means of distinguishing between current and cleared HCV infections that is well correlated with HCV RNA testing.The method currently recommended for identifying subjects with hepatitis C virus (HCV) infection is an enzyme immune assay (EIA) for the detection of anti-HCV antibodies (16). However, this assay sometimes generates false-positive or false-negative results. Furthermore, it is not always possible to distinguish between current and past cleared infections. Thus, supplementary tests are required. The strip immunoblot assay, a more specific anti-HCV serological test, is useful to distinguish true-positive from false-positive EIA results. Positive results from nucleic acid testing (NAT) for HCV RNA indicate active HCV infection (1). Assays that detect the HCV core antigen (Ag) have been developed to diagnose current HCV infection. The first such assay developed was a qualitative assay, conceived for screening blood donations. This assay increased viral safety by significantly reducing the length of the window preceding seroconversion (4, 13). A second test was subsequently developed for the detection and quantification of total HCV core antigen (Trak-C; Ortho-Clinical Diagnostics, Raritan, N.J.). This assay, incorporating an immune complex dissociation step, was designed for blood donation screening (3...

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