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Evaluation of Third‐Generation Screening and Confirmatory Assays for HCV Antibodies

A third‐generation (gen.) screening and immunoblot assay (Ortho EIA‐3.0; Chiron RIBA‐3 prototype), using antigens derived from the capsid and different nonstructural regions (NS3, NS4 and NS5) of the hepatitis C virus viral genome, were evaluated in comparison with the corresponding second‐gen. assays (Ortho EIA‐2.0; revised Ortho EIA‐2.5; Chiron RIBA‐2). In 203 depository sera of blood donors, positive in EIA‐2.0, specificity of the screening assays was improved as shown by an increase in positive predictive value for viral carrier state from 0.23 (EIA‐2.0) to 0.37 (EIA‐2.5) and 0.52 (EIA‐3.0). Comparing the confirmation patterns on RIBA‐2 and RIBA‐3, this amelioration was mainly due to the specific elimination of false‐positive c22‐3 and c100‐3 reactions. Antibody response to the newly added NS5 antigen was not as prevalent as to the other antigens and had only a minor influence in sample allocation. In contrast, screening of 1,560 volunteer blood donors and 47 hemodialysis patients revealed 3 additional positive sera, only reacting with the NS5 antigen. However none of these isolated NS5 reactions could be confirmed on synthetic peptides [INNO‐LIA: NS5(p)] and none was PCR positive. A documented seroconversion, detected earlier with EIA‐3.0, was related to a better immunological response to the NS3 antigen and not to the additional NS5. From this pilot study third‐gen. assays appeared extremely useful in the reevaluation of HCV‐seropositive depository sera. However the additional value of the NS5 antigen in blood donor screening is still hypothetical and remains to be established in larger screening studies.