Quantification of Core Antigen Monitors Efficacy of Direct-acting Antiviral Agents in Patients With Chronic Hepatitis C Virus Infection

BACKGROUND & AIMS: Widespread use of direct-acting antiviral (DAA) agents to treat patients with hepatitis C virus (HCV) infection has reduced the need for monitoring of HCV RNA levels, because viral kinetics do not predict sustained virologic response (SVR) to these drugs. However, the performance of cheaper tests such as the assay to quantify HCV core antigen (HCV Ag) has not been determined. We investigated the accuracy of the HCV Ag test in predicting which patients receiving DAAs will achieve SVRs at week 12 (SVR12). METHODS: We performed a prospective study of 58 patients infected with HCV genotypes 1-5 (45% with HCV genotype 1, 72% with cirrhosis) receiving DAA therapy from the Liver Center at the Universita degli Studi of Milan in Italy from January to March 2015. We collected blood samples and measured levels of HCV Ag and HCV RNA at baseline, after 2 and 4 weeks of treatment, the end of treatment, and 12 weeks after treatment ended. We compared the ability of these assays to predict which patients would have SVR12. RESULTS: The median baseline level of HCV RNA was 5.79 log10 IU/mL (range, 3.51-7.31 log10 IU/mL) and of HCV Ag was 3226.87 fmol/L (range, 17.30-54,927.00 fmol/L). HCV Ag became undetectable in 71% of patients at week 2, 84% at week 4, and 93% at the end of treatment. HCV RNA became undetectable in 10% of patients at week 2, 43% at week 4, and 100% at the end of treatment (P < .0001). Concordance between the tests in identifying patients who would achieve SVR12 was 40% at week 2, 55% at week 4, and 95% at the end of treatment. Fifty-three of 58 patients (91%) achieved an SVR12; the test for HCV Ag identified 97% of these patients. The tests for HCV Ag and HCV RNA predicted which patients would have SVR12 with positive predictive values of 90% vs 83%, respectively, at week 2 and 89% vs 92%, respectively, at week 4. CONCLUSIONS: Tests that measure HCV Ag monitor efficacy of DAA therapy for HCV infection as well as assays that measure HCV RNA and can be recommended for clinical practice. However, measurement of HCV RNA after treatment can rule out relapse in HCV Ag-positive patients.