Comparative analysis of viral load quantification in clinical samples with low detectable HCV viremia

The accurate determination of HCV viral load is essential for evaluating the response to antiviral therapy and to determine the duration of treatment. New “stopping rules” in the lower range of quantification have been defined. These stopping rules and rules for responseguided therapies are based on viral load results generated during the clinical phase II/III studies by using the Roche High-Pure-System/COBAS TaqMan assay v2 (HPS). Numerous systems for quantification of HCV viral load are currently available, such as RealTime HCV (Abbott), COBAS Ampliprep/COBAS TaqMan HCV (Roche) and COBAS AmpliPrep/COBAS TaqMan HCV Quantitative Test, version 2.0 (Roche), artus HCV QS-RGQ (Qiagen) and VERSANT HCV RNA 1.0 (Siemens, for use on the kPCR system) and there is little information on the comparability of results obtained from these systems. The aim of this study was to determine and compare the variation between these systems in the low range encompassing the clinical decision points of the different treatment schemes. 2 ), determined based on serially diluted PEI Standard, were similar for RealTime (0.99) and CAP/CTM v1.0 (0.99), while lower R 2 values were determined for CAP/CTM v2.0 (0.92) and kPCR (0.91) (Fig. 1). Similar correlation coefficients were determined with serial dilutions of the 3rd WHO standard for kPCR and RealTime (0.97 each), while CAP/CTM v2.0 (0.82) and artus QS-RGQ (0.61) showed lower R 2 values (Fig. 2). CAP/CTM v1.0 also demonstrated correlation of 0.99 for PEI- and WHO-standards, when dilution steps set at 100 IU/ml and below were excluded due to lower limit of quantification. Quantification results were higher with CAP/CTM v1.0 in comparison to CAP/CTM v2.0. Within the lower dilution range from 5 IU/mL to 25 IU/mL, RealTime “detected” 16/18 samples from both standards, while a lower number of samples was detected by CAP/CTM v1.0 (14/18), Versant kPCR (10/18), artus QS-RGQ (9/18) and CAP/CTM v2.0 (8/18), respectively (Tab. 1A / 1B). The highest precision expressed by the lowest coefficient of variation (CV) was obtained with the RealTime HCV assay for the two clinical samples at 100 IU/mL (Fig. 3).