Objective To study the significance of the sample S/Co ratio when using a domestic reagent for anti-hepatitis C virus(HCV)antibody detection and to explore the procedure and standard of anti-HCV antibody diagnosis by using this domestic reagent.Methods Anti-HCV antibody was detected in 295 000 blood donors by a domestic anti-HCV reagent with enzyme-linked immunosorbent assay(ELISA)method and the reactive samples were tested again by ortho anti-HCV antibody reagent.The samples which anti-HCV antibodies were determined as positive by ortho anti-HCV rea- gent were examined by recombinant immunoblot assay(RIBA)reagent and 106 samples of them were also tested for HCV RNA.Results Six hundred and eighty-one samples were reactive in 295 000 samples screened by the domestic ELISA reagent,the reactive ratio was 0.23 %.Among the reactive samples screened by the domestic ELISA reagent,367 samples were determined as positive by ortho anti-HCV reagent while 66.2% of them showed a S/Co ratio≥3.8.The consistency rate between positive results determined by the domestic reagent and RIBA reagent respectively was 53.8%.For the samples showing S/Co ratio≥3.8 by ortho anti-HCV reagent,94.2% had a S/Co ratio≥8.0 when using the domestic ELISA reagent,while the percentage of samples showing S/Co ratio