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Journal of Clinical Microbiology, August 1999, p. 2525-2532, Vol. 37, No. 8
0095-1137/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Genotype Dependence of Hepatitis C Virus Load Measurement in Commercially Available Quantitative Assays

Janet Mellor, Anna Hawkins, and Peter Simmonds*

Department of Medical Microbiology, University of Edinburgh, Edinburgh EH8 9AG, United Kingdom

Received 28 December 1998/Returned for modification 16 March 1999/Accepted 29 April 1999

Standardization and genotype independence of methods used to quantify hepatitis C virus (HCV) RNA in clinical specimens are necessary for accurate assessment of the role of HCV quantitation as a prognostic marker for HCV infection and monitoring of the response to antiviral treatment. Commercially available methods used to measure HCV loads include PCR-based (Roche Monitor) and hybridization-based (Quantiplex bDNA-2) methods. Recently, a new version of the Roche Monitor assay (version 2.0) has become available; it has been modified to achieve more equal quantitation of different HCV genotypes. Consistent with previous reports, Roche Monitor version 1.0 substantially underestimated concentrations of RNA transcripts of types 2b, 3a, 4a, 5a, and 6a and virus loads in individuals infected with genotypes 2 to 6 relative to reference tests. However, version 2.0 achieved equivalent quantitation of each genotype over a narrow quantitative range (103 to 5 × 105 copies of RNA/ml) but significantly underestimated RNA concentrations above this range. The assay showed an equivalent inability to quantify high levels of HCV RNA in plasma samples, and this was responsible for the falsely narrow range of virus loads detected in HCV-infected individuals. In contrast, the Chiron bDNA-2 assay could only measure RNA concentrations in the upper quantitative range (2 × 105 to 5 × 107 copies of RNA/ml) but showed equivalent sensitivity for genotypes 1 to 5; however, concentrations of type 6a RNA transcripts and virus loads in clinical specimens from individuals infected with type 6a were underestimated by a factor of 2 to 4. Differences were observed between PCR- and hybridization-based assays in their relative quantitation of HCV RNA transcripts and HCV genomic RNA, which may cause problems with the use of transcripts for interassay calibration.

* Corresponding author. Mailing address: Department of Medical Microbiology, University of Edinburgh, Teviot Place, Edinburgh EH8 9AG, United Kingdom. Phone: 44 131 650 3138. Fax: 44 131 650 6531. E-mail: Peter.Simmonds{at}ed.ac.uk.

Journal of Clinical Microbiology, August 1999, p. 2525-2532, Vol. 37, No. 8
0095-1137/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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