Performance of a conventional enzyme immunoassay for hepatitis C virus core antigen in the early phases of hepatitis C infection.

There are periods within the early phase of hepatitis C virus (HCV) infection in which the anti-HCV antibody test is unable to confirm HCV viremia. To reduce the risk of transmitting HCV through transfusions, we developed a simple and highly sensitive enzyme immunoassay (EIA) which detects the core antigen of HCV (HCVcAg). This assay employed a conventional colorimetric EIA system, and was based on a two-step sandwich assay, using a 96- well microplate. The reproducibility of the results was very high. When the cutoff values were set to 30 fmol of recombinant HCVcAg/L, as determined by the distribution of healthy subject sera (n=223), 99.6% of healthy subject sera and 100% of hepatitis B patient sera (n=50) were negative for HCVcAg. The clinical performance of this EIA was examined using 14 commercially available seroconversion panels. In every panel, HCVcAg could be detected at points preceding the seroconversion of anti-HCV antibodies. The points at which HCVcAg was detected were the same as those at which it was detected by an AMPLICOR HCV Monitor test. The EIA's window period for detecting the HCVcAg in all panels was on average 26 days shorter than that of the anti-HCV antibody test. In three panels where the first sample is negative for HCV RNA, the window period was shortened 50 days by this EIA for HCVcAg. There was a positive correlation between the concentration of HCVcAg and HCV RNA in anti-HCV antibody negative specimens. This assay was simpler to perform than assays based on gene amplification technology for the detection of HCV RNA, and the window period was shortened to that of the AMPLICOR HCV Monitor test. Thus, the EIA for HCVcAg would be useful in screening seroconverting donors and could reduce the residual risk of secondary HCV infections through transfusions.