High rate of false positives in blood donor screening for antibodies to hepatitis C virus. Cause of underestimation of virus transmission rate?

Anti-hepatitis C virus antibody screening of blood donors in different countries revealed prevalences ranging from 0.4-1.4%. These results were obtained with an enzyme immunoassay based on a recombinant hepatitis C virus antigen. We applied a specific inhibition assay (neutralization assay) and a recombinant immunoblot assay to determine the specificity of positive reactions in the enzyme immunoassay. Of 2836 blood donor sera tested, 10 (0.35%) were reactive in the enzyme immunoassay, however, only 3 sera (0.1%) proved to be specifically anti-HCV positive in the inhibition assay. The recombinant immunoblot assay gave similar results. The prevalence of anti-hepatitis C virus antibodies among blood donors has been overestimated in recent publications. Furthermore the high rate of false positives in the enzyme immunoassay may explain reports claiming that only a minor part of EIA positive blood units transmitted the hepatitis C virus to recipients. The inhibition assay was also applied to sera of haemophiliacs and of patients with hepatopathy which had reacted positively in the anti-hepatitis C virus antibody enzyme immunoassay. The anti-hepatitis C virus specificity was confirmed for all sera from the haemophiliacs group (100%) and for 77% of the hepatopathy patients group. Thus, the anti-hepatitis C virus enzyme immunoassay has a high predictive value when it is used to screen groups with high risks of parenteral hepatitis C virus infection, however, its predictive value is very low when it is used for blood donor screening.