Differences between quantification of genotype 3 hepatitis C virus RNA by Versions 1.0 and 2.0 of the COBAS AmpliPrep/COBAS TaqMan HCV Test.

Background: Differences between the designs of hepatitis C virus (HCV) viral load assays can result in genotype-related variability in RNA quantification. We tested paired aliquots of plasma specimens from HCV-infected individuals using two versions (v1.0 and v2.0) of the Roche COBAS AmpliPrep/COBAS TaqMan HCV Test (CAP/CTM HCV) and noted variability between results for a subset of specimens; we then sought to determine whether discrepant results were more prevalent among specific HCV genotypes.

Methods: Archived and prospectively-collected plasma samples from 114 unique patients were tested using CAP/CTM HCV v1.0 and v2.0. The HCV genotype result for each patient was determined by retrospectively reviewing laboratory records.

Results: All (46/46) specimens with quantifiable viral loads from patients with genotype 1 or 2 infection had CAP/CTM HCV v1.0 and v2.0 results that were within 0.5 log10 IU/mL; in contrast, only 3/11 (27.3%) from patients with HCV genotype 3 (mean difference, 0.56 log10 IU/mL higher with v2.0) and 0/3 (0%) from patients with HCV genotype 4 (mean difference, 0.91 log10 IU/mL higher with v2.0) had results within 0.5 log10 IU/mL. Among specimens with detectable HCV RNA below the lower limit of quantification with v1.0, greater proportions of genotype 3 (4/7, 57.1%) and genotype 4 (3/4, 75.0%) specimens than genotype 1 or 2 specimens (6/30, 20.0%) had v2.0 results within the quantifiable range.

Conclusions: In patients infected with HCV genotype 3, sequential CAP/CTM HCV viral load results should be compared with caution and interpreted in the context of the specific assay version used.