Comparison of a hepatitis C core antigen assay to nucleic acid amplification testing for detection of hepatitis C viremia in a US population

The prevalence of hepatitis C virus (HCV) infection in the United States has increased over the past decade despite the development of effective direct-acting antiviral treatments. To meet the World Health Organization's (WHO) goal of eliminating HCV infection by 2030, transmission events must be reduced. Currently, infection screening relies on detection of HCV antibodies, with nucleic acid amplification testing (NAAT) used to confirm HCV viremia and monitor changes in viral load. However, the seroconversion window for detection of HCV antibodies is long, averaging 6 weeks, with delayed seroconversion common in co-infected and immunosuppressed populations. Testing for HCV core antigen, which is present approximately 5 weeks before HCV antibodies, holds promise for earlier detection of HCV infection. It may also hold promise as a cheaper, more accessible, and more rapid alternative to NAAT for infection confirmation. Here, we evaluated the agreement between a research-use HCV Core Antigen Assay and NAAT among US patients receiving clinically indicated NAAT. Among 412 specimens, the overall concordance was 97.1%, with a positive percent agreement of 95.5%. Discrepancies primarily occurred among patients with chronic HCV and low viral loads; 11/12 discrepancies showed viral loads