- BACKGROUND: Screening blood units for hepatitis C virus (HCV) with nucleic acid testing (NAT) reduces the risk associated with the long “window period” (8-9 weeks) after HCV infection. The feasibility of adding the HCV core antigen assay in pools to the existing anti-HCV individual screening was examined as an alternative of NAT, for early detection of HCV. STUDY DESIGN AND METHODS: Eighteen HCV seroconversion panels were tested for HCV antibodies, HCV antigen, and HCV RNA. Each sample was tested for HCV antigen individually and in pools of 3, 6, and 12. Statistical analyses included estimation of time until detection of the first positive HCV antigen bleed in each pool size, with a locally weighted regression (LOWESS) model. Sensitivity was calculated compared to NAT. RESULTS: Detection of HCV antigen in individual samples and in pools of 3 and 6 significantly preceded the detection of antibodies by 63, 53, and 46 days, respectively. Although the sensitivity of the HCV antigen test decreased with the increase in pool size, the estimated overall sensitivity of the “two-stage” antigen and antibody screening (where NAT of individual samples was the gold standard) was not significantly different between individual and the different pool sizes. CONCLUSION: Screening for HCV antigen in pools of 6 can be considered an efficient and easier-to-implement alternative to the costly NAT for identifying blood donors in the seroconversion period. It may offer a cost-effective approach in resource utilization in poor countries, that, after the implementation of HCV antibody testing, want to further improve blood safety.