Evaluation of the cobas® HCV test for quantifying HCV RNA in dried plasma spots collected using the cobas® Plasma Separation Card

Abstract

Objective: This study evaluated the performance of the cobas® hepatitis C virus (HCV) Test for use on the cobas® 6800/8800 Systems for the detection and quantification of HCV RNA collected using the cobas® Plasma Separation Card (PSC) compared with plasma samples.

Methods: Whole EDTA-venous blood was collected from 50 HCV-positive donors and 140 μL from each donor was spotted onto a PSC and stored either frozen or at ambient temperature. These were compared with matched EDTA-plasma samples. The limit of detection (LoD) of the assay for PSC samples was determined using serial dilutions of the Roche HCV secondary calibration standard. The stability of the PSC samples across a range of timepoints was also assessed.

Results: The mean titer difference between ambient and -10 °C storage of PSC samples was 0.04 log10 IU/mL (95% CI: 0.00, 0.07). The mean titer difference between frozen PSC samples and EDTA plasma samples was -1.59 log10 IU/mL (95% CI: -1.66, -1.53) and between ambient PSC samples and EDTA samples was -1.64 log10 IU/mL (95% CI: -1.70, -1.57). Correlation between PSC samples and EDTA plasma was linear in both cases (frozen: slope = 1.039, intercept=-1.839, R² = 0.89; ambient: slope = 1.012, intercept=-1.712, R² = 0.88). The LoD of the cobas® HCV Test using the PSC was 866 IU/mL (95% CI: 698, 1153 IU/mL) and 408 IU/mL (95% CI: 336, 544 IU/mL) using an optimized Assay Specific Analysis Package.

Conclusions: PSC samples correlate well with plasma viral load and demonstrate a LoD below 1000 IU/mL and good stability at ambient temperature for 28 days. A correction factor would allow quantification of HCV viral RNA load from samples collected using a PSC.

Keywords: Cobas; Detection; Dried blood spot; Hepatitis C virus; Plasma separation card; Quantification.