Hepatitis C core antigen: Diagnosis and monitoring of patients infected with hepatitis C virus.

New efficient strategies are needed for the assessment of active hepatitis C virus (HCV) infection. The aim of this study was to evaluate the ability of HCV core antigen (HCV-cAg) as a marker of active HCV infection in newly diagnosed patients, for treatment monitoring, and for the detection of therapeutic failure. A prospective study was conducted at a regional reference hospital in Spain. HCV-cAg and viral load (RNA-HCV) were tested in plasma or serum samples from three patient groups: new diagnosis, treatment monitoring, and treatment failure. The treatment monitoring group was tested at the beginning of treatment, at 4 weeks post-initiation, at the end of treatment, and at 12 weeks post-treatment completion. The Architect HCV core antigen assay was performed for HCV-cAg testing, and viral load was quantified with the Cobas 6800 system. A total of 303 samples from 124 patients were analyzed. Excellent correlation was seen between HCV-cAg and HCV-RNA (R2=0.932). The optimal cut-off value was 3fmol/l in the receiver operating characteristics curve analysis, and the area under the curve was 0.987 (95% confidence interval 0.972-1.000). HCV-cAg sensitivity and specificity were 97% and 95%, respectively. Most diverging results were observed in the treatment follow-up group. HCV-cAg demonstrated good sensitivity and specificity as a marker for active HCV infection, new diagnosis, detection of antiviral therapeutic failure, and treatment monitoring.