Quantitative measurement of HCV RNA in the serum: a comparison of three assays based on different principles.

Quantitative measurement of hepatitis C virus (HCV) RNA is useful in patients with chronic hepatitis C, especially with interferon treatment. We examined the clinical usefulness of the AMPLICOR monitor assay, a newly developed assay for quantitative measurement, by comparing it with two other assays with different principles. A total of 48 patients with chronic hepatitis C who were treated with interferon-alpha (IFN-alpha) were studied: 19 were complete responders and 29 were non-responders. Hepatitis C virus RNA was measured quantitatively by AMPLICOR, branched DNA (bDNA) probe, and competitive polymerase chain reaction (C-PCR) assays. An internal quantification standard was used in the AMPLICOR assay. A cDNA competitor with a deletion of 15 base pairs in the middle portion was used in the C-PCR method. The concentration of HCV RNA was significantly correlated between the three assays adopted in this study. Sensitivity of assays was 100% by C-PCR, 90% by AMPLICOR and 69% by bDNA assays. The active quantitative range was best with the C-PCR assay and worst with the bDNA assay. The bDNA assay had a tendency to exhibit lower values for patients with serotype 2 than did the other two assays. The predictive rate of the long-term response to IFN-alpha therapy, before its initiation, was over 75% in all three assays. The predictive rate just after completing IFN-alpha therapy was as high as 80% by C-PCR and the AMPLICOR assays, but was low (58%) with the bDNA assay. The handling of the bDNA and AMPLICOR assays was much easier than the C-PCR assay, which required time and skill. These results indicate that the AMPLICOR assay is a simple and reliable method for measuring the serum concentrations of HCV RNA, and thus is suitable for clinical application.