Abstract: Objective  To determine the optimal signal-to-cutoff (S/CO) value of the positive predictive value of hepatitis C virus  (HCV) antibody ≥ 95%,and to determine the medical decision level of the laboratory and to establish the methodology for exploring the 95% positive confidence intervals for different systems of HCV antibody detection reagents. Methods  From July 2021 to February 2022,a total of 282 plasma samples from outpatients and inpatients in Beijing Ditan Hospital,Capital Medical University were subjected to both the initial screening of chemiluminesent immunoassay (CLIA) and HCV RNA testing.Among the samples,252 showed reactivity in the antibody initial screening (S/CO ≥ 1),while 30 samples tested negative; supplemental confirmation test of recombinant immunoblot assay (RIBA) was performed and the results of HCV RNA were consulted. The antibody S/CO value of HCV infection was obtained by receiver operating characteristic  (ROC) curve when the positive predictive value in our laboratory was ≥ 95%.  Results  The 30 samples tested negative in the initial screening also showed negative results for HCV RNA testing and RIBA. Excluding 16 cases with unclear history of HCV infection,among 236 samples with HCV antibody S/CO ≥ 1,188 samples were true positive and 48 samples were negative. ROC analysis showed that the optimal S/CO value was 7.83,the sensitivity was 93.09%,the specificity was 95.83% and the area under the curve (AUC) was 0.98. (P < 0.000 1). Conclusion  It is helpful for clinical diagnosis and treatment to provide the antibody S/CO value of HCV infection when the positive predictive value was ≥ 95% in our laboratory.

Key words: hepatitis C virus antibody, recombinant immunoblotting assay, receiver operating characteristic curve, positive predictive value