Results of HCV screening of volunteer blood donors with a chemiluminescent immunoassay and a second- or third-generation EIA: overlap of false-positive reactivity and its impact on donor management

BACKGROUND: This study reports the results of adopting a strategy of anti-HCV testing of volunteer blood donors that uses a primary screening assay, two secondary EIAs (Anti-HCV Version III, Murex; Monolisa Anti-HCV New Antigens, Sanofi Pasteur), and a confirmatory immunoblot (HCV WE, Murex). STUDY DESIGN AND METHODS: A comparison was made of HCV test results from volunteer donors tested in two periods when different primary HCV screening assays were in use. The same two secondary screening assays and the same confirmatory test were used for the whole study. The two different primary assays were semi-automated second- or third-generation HCV EIA (Abbott Diagnostics) and an HCV chemiluminescent immunoassay (ChLIA), performed on a fully automated analyzer (PRISM, Abbott). RESULTS: During the period of use of the EIAs as primary screening assays, there were 60 donors per year who were confirmed as anti-HCV-positive, 29 who were classed as having indeterminate HCV serologic results, and 236 who were assessed as having biologically false-positive anti-HCV results. These numbers compared with 57, 52, and 320 such donors, respectively, in the first year of routine use of the ChLIA. The significant increase (p<0.05) in the number of anti-HCV-indeterminate donors after the introduction of the ChLIA was primarily due to an increase in donors who reacted on Monolisa HCV, but not an HCV Murex (expected 18/year vs. the observed 31/year, p<0.01). CONCLUSIONS: Compared to the second- or third-generation HCV EIA, the HCV ChLIA has a significantly greater overlap of false reactivity with the Monolisa HCV assay. This finding has implications for the selection of primary and secondary assays for anti-HCV screening of blood donors.