HCV RNA assay sensitivity impacts the management of patients treated with direct-acting antivirals

Background: Application of response-guided therapy (RGT) rules to the treatment of HCV infection with pegylated interferon-alpha 2a and ribavirin, and direct-acting antivirals (DAAs) such as the NS3/4A protease inhibitors (PIs) boceprevir and telaprevir, relies on the determination of viral genotype and on-treatment HCV RNA level. Currently there are few data available regarding the clinical impact of the analytical differences that exist between different HCV RNA quantification assays on treatment decisions such as those involved in RGT. Methods: We sought to ascertain the concordance between two HCV RNA quantification assays, the Roche/High-Pure-System COBAS (R) TaqMan (CTM) version 2 and Abbott RealTime HCV (ART), and to understand the impact of different assay characteristics on treatment decisions. We evaluated 1,336 specimens collected from 74 patients enrolled in the Phase II CHAMPION-2 study of the investigational DAAs ABT-450 (an acylsulfonamide NS3/4A PI), ABT-072 and ABT-333 (both non-nucleoside NS5B polymerase inhibitors). Results: HCV RNA level results were highly correlated, but CTM values were higher than those from ART by an average of 0.46 log IU/ml. Use of ART HCV RNA level results led to a higher positive predictive value of week 4 viral load for the achievement of a sustained virological response 24 weeks after the end of treatment (100% versus 87% using the lower limit of detection as the threshold). Conclusions: This study suggests that HCV viral load assay performance characteristics need to be taken into consideration when managing HCV patients with RGT. Further studies are required to determine whether a consensus HCV RNA level threshold can be established or whether HCV viral load assays with greater sensitivity can increase cure rates with RGT.