Dynamic range of hepatitis C virus RNA quantification with the Cobas Ampliprep-Cobas Amplicor HCV Monitor v2.0 assay

Abstract

Accurate quantification of hepatitis C virus (HCV) RNA is needed in clinical practice to decide whether to continue or stop pegylated interferon-alpha-ribavirin combination therapy at week 12 of treatment for patients with chronic hepatitis C. Currently the HCV RNA quantification assay most widely used worldwide is the Amplicor HCV Monitor v2.0 assay (Roche Molecular Systems, Pleasanton, Calif.). The HCV RNA extraction step can be automated in the Cobas Ampliprep device. In this work, we show that the dynamic range of HCV RNA quantification of the Cobas Ampliprep/Cobas Amplicor HCV Monitor v2.0 procedure is 600 to 200,000 HCV RNA IU/ml (2.8 to 5.3 log IU/ml), which does not cover the full range of HCV RNA levels in infected patients. Any sample containing more than 200,000 IU/ml (5.3 log IU/ml) must thus be retested after dilution for accurate quantification. These results emphasize the need for commercial HCV RNA quantification assays with a broader range of linear quantification, such as real-time PCR-based assays.

FIG. 1.

Relationship between the HCV RNA levels measured in the undiluted (neat) and diluted samples in the Cobas Amplicor HCV Monitor v2.0 assay after HCV RNA extraction in the Cobas Ampliprep device. All samples falling above 100,000 IU/ml (5.0 log IU/ml) were retested after 1/100 dilution. The regression line is shown as a solid line, in comparison with the main diagonal (dashed line).

FIG. 2.

Median value and distribution of the log HCV RNA level in the diluted sample minus the log HCV RNA level in the undiluted (neat) sample, according to the initial viral level in the undiluted sample.

FIG. 3.

Proportion of samples for which a difference of more than 0.3 log (twofold; gray-shaded columns) and more than 0.5 log (threefold; black-shaded columns) was found between the HCV RNA levels measured in the undiluted (neat) and the diluted sample, respectively, according to the initial viral level in the undiluted sample.