Significance of the signal‐to‐cutoff ratios of anti‐hepatitis C virus enzyme immunoassays in screening of Chinese blood donors

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Abstract
BACKGROUND: The correlation between signal‐to‐cutoff (S/CO) ratios of a second‐generation hepatitis C virus (HCV) enzyme immunoassay (EIA; Abbott) and a third‐generation HCV enzyme‐linked immunosorbent assay (ELISA; Ortho) and confirmed HCV infection has been reported. The utility of the values for the Chinese anti‐HCV EIA kits, however, has not been studied in evaluating test results in Chinese blood donors. STUDY DESIGN AND METHODS: A total of 156 donor samples repeat reactive for anti‐HCV at routine screening from five representative regions of China were retested for anti‐HCV by the Ortho third‐generation HCV ELISA and six Chinese EIA kits and for HCV RNA by a human immunodeficiency virus‐1 and HCV assay (Procleix, Chiron Corp.). The HCV RNA–nonreactive samples were further tested for anti‐HCV by a third‐generation recombinant immunoblot assay RIBA (Chiron Corp.). The positive result by either nucleic acid amplification test or RIBA was interpreted as confirmed HCV infection. RESULTS: The confirmed HCV prevalence rate in donors in five representative regions obtained in this study was 0.20 percent (77/37,900) in 2004. All seven anti‐HCV EIA kits had a significant correlation between S/CO ratios and confirmed HCV infection. The threshold S/CO ratios, which predicted more than 95 percent of confirmed HCV infections for the Ortho, SABC, BGI‐GBI, InTec, GWK, KHB, and WANTAI kits, were 3.8, 6.0, 7.0, 8.6, 10.0, 10.0, and 14.0, respectively. CONCLUSIONS: Anti‐HCV EIA kits commonly used in Chinese donors screening demonstrate good correlation between S/CO ratios and the confirmed infection. For the Ortho third‐generation HCV ELISA, the S/CO ratio of 3.8 determined by the US Centers for Disease Control and Prevention is applicable to Chinese blood donors. The Chinese domestic EIA kits evaluated show a diverse range of threshold S/CO ratios.
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