Antibodies to hepatitis C virus in low-risk blood donors: implications for counseling positive donors

The significance of antibodies to hepatitis C virus (HCV) found by screening enzyme-linked immunoassay testing in a low-risk blood donor population is unclear. The rate of false positivity in this group as well as the usefulness of supplemental testing were examined by correlating the results of two screening enzyme-linked immunoassays (Ortho Diagnostics, Raritan, NJ, and Abbott Laboratories, North Chicago, IL) with supplemental antibody testing by the recombinant immunoblot assays (1 and 2) (Ortho) and neutralization assay (Abbott). Polymerase chain reaction was used to detect HCV genomic RNA to confirm viremia. Among 11.243 volunteer donors who were screened for the presence of antibodies to HCV by enzyme-linked immunoassay, 60 (0.53%) sera were repeatedly reactive. Twenty-five of these 60 sera were available for further testing. Seven sera were reactive by both screening enzyme-linked immunoassays, as well as by both recombinant immunoblot and neutralization assays. Six of these seven sera had detectable HCV genomic RNA by polymerase chain reaction. Among the remaining 18 sera, none were reactive by either recombinant immunoblot assays, whereas two sera were reactive by the neutralization assay only. None of the 18 samples had detectable HCV genomic RNA. Five of the six sera with elevated aminotransferase levels were among the seven sera reactive by all immunoassays. It is concluded that there is a significant false positivity rate associated with screening enzyme-linked immunoassay testing in a low-risk blood donor population. Supplemental testing correlates well with detection of hepatitis C genomic material by polymerase chain reaction and identifies donors who are truly infected.