Introduction Screening high-risk populations for hepatitis C (HCV) using antibody (anti-HCV) does not immediately distinguish resolved and active infections and may miss acute infections. HCV core-antigen (HCVAg) screening has been introduced in laboratories supporting some UK sexual health clinics. We evaluated Abbott Architect’s automated HCVAg immunoassay for HCV screening.
Methods Testing was introduced in May 2015 for those reporting HCV risk in the past 6 months, and annual screening for all HIV-positive individuals. HCVAg-positive samples were tested in duplicate, then tested for HCV–RNA. Few samples were tested for both HCVAg and HCV-RNA in the initial few months. Results for all tests performed May 2015–April 2016 were reviewed.
Results 5132 samples were tested for HCVAg. 113/5132(2%) were HCVAg positive. 139 samples had both HCVAg and HCV-RNA tested. Using HCV-RNA as the gold standard, HCVAg sensitivity was 99%; positive predictive value 63%. Specificity was 39%; negative predictive value 96%.
The HCVAg negative/HCV-RNA positive individual had low viral load (130c/ml).
Of the 41 HCVAg positive/HCV-RNA negative individuals; 30(73%) were retested later and were HCVAg negative and HCV-RNA or anti-HCV negative. 3(7%) were persistently HCVAg positive but HCV-RNA negative; 7 had no follow up samples; 1 subsequently became HCV-RNA positive.
Discussion The specificity of HCVAg in our cohort is lower than that published in a recent systematic review (93% sensitivity/99% specificity). False positive results cause distress for patients and additional laboratory costs, however the increased sensitivity for acute infection may lead to earlier diagnosis in high-risk populations.
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