Study on the significance of S/Co ratio of a domestic reagent used for anti-hepatitis C virus antibody detection

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 ratio8.0 by domestic reagent was 99.2% among the samples showing S/Co ratio3.8 by ortho anti-HCV reagent.Two hundred and twenty-three(60.8 %)samples were HCV RIBA positive in 367 positive samples determined by ortho reagent.HCV RIBA positive rate was 95.7% in S/Co≥8.0 samples determined by the domestic ELISA reagent and only 2.2% in S/Co8.0 samples.Forty-two samples were HCV RNA positive in 106 HCV antibody positive samples determined by ortho anti-HCV reagent.Conclusions There is a high false positive rate when using the domestic ELISA reagent for HCV antibody screening in blood donors.This problem will result in the waste of the blood resource and donors.There is a relationship between samples showing S/Co≥8.0 by domestic ELISA HCV reagent and samples showing S/Co≥3.8 by ortho anti-HCV reagent,which may be helpful for anti- HCV antibody detection.