Optimizing Signal to Cut-off Values (S/Co) of Anti-HCV in Prediction of Viremia: A Retrospective Analysis with HCV-RNA

Objective: The prevalence of chronic hepatitis C worldwide is defined in three categories: low (<2.5%), medium (2.5-10%) and high (>10%) while the prevalence of it is seen between 0.5-1.9% in Turkey. This study aims to identify the most appropriate signal to cut-off (S/Co) value to observe viremia and decrease the number of unnecessary hepatitis C virus-ribonucleic acid (HCV-RNA) analyzes due to false positive anti-HCV results. Methods: A retrospective analysis was performed regarding the relationship of HCV-RNA and anti-HCV results between January 2019-September 2021. Adult patients (18+ age) with reactive anti-HCV and HCV-RNA results were included in the study. Results: A total of 626 patients were included (median age 49.7; standard deviation +/- 18.2), of which 352 (56.2%) were female and 274 (43.8%) were male. Despite their seropositivity, 595 (95%) patients were HCV-RNA negative and only 31 (%5) patients were positive. Non-parametric MannWhitney U test was used to compare anti-HCV results regarding HCV-RNA positive and negative patients. Anti-HCV levels in the HCV-RNA positive group of patients (median =13.7) were significantly higher compared with the HCV-RNA negative group (median =1.1) (p=0.001). HCV-RNA was accepted as the gold standard in receiver operator characteristic (ROC) analysis to define the most accurate cutoff value which was found to be 8.9 S/Co. Sensitivity and specificity were 93% and 91%, respectively [area under the curve (AUC): 0.94] (95% confidence interval: 0.907-0.974). AUC was significantly over 0.5 (p=0.001). Conclusion: It is essential for laboratories to modify reference values according to their patient populations and prevalence. 8.9 S/Co was defined as the most appropriate value for anti-HCV in our laboratory and below this, additional interventions and retesting should be performed prior to the report.