Abstract
The efficacy of interferon therapy for hepatitis C virus (HCV) infection improved remarkably. However, virologic relapse occurs in a substantial proportion of patients with virologic response (defined as an HCV RNA level below 50 IU/ml at the end‐of‐treatment). A highly sensitive RT‐nested PCR assay capable of detecting almost a single copy of HCV RNA and a real‐time RT‐PCR assay to quantify HCV RNA down to 120 copies per ml were developed. The RT‐nested PCR assay showed that 1 IU of HCV RNA is equivalent to 12.2 copies. For 28 patients with virologic response (12 relapsers and 16 sustained virologic responders), week‐4 and end‐of‐treatment plasma samples were retested. At week 4, HCV RNA was detected by the RT‐nested PCR and qualitative COBAS Amplicor HCV version 2.0 in 8/9 (89%) and 6/9 (67%) samples from relapsers, and in 4/16 (25%) and 2/16 (13%) samples from sustained virologic responders, respectively. End‐of‐treatment samples with HCV‐negative by the qualitative COBAS Amplicor were positive by the present assay in 4/12 (25%) of relapsing patients and 0/16 (0%) of sustained virologic responders. The viral levels detected by the present assay in the Amplicor‐negative samples were 3.5–17.3 copies/ml, which is below the detection limit of COBAS Amplicor. In conclusion, the highly sensitive RT‐nested PCR assay can predict sustained virologic response at week 4 and virologic relapse at the end‐of‐treatment more accurately than COBAS Amplicor, suggesting its usefulness in monitoring antiviral therapy for HCV infection. J. Med. Virol. 79: 1113–1119, 2007. © 2007 Wiley‐Liss, Inc.