Multicenter Evaluation of the Cepheid Xpert Hepatitis C Virus Viral Load Assay

Abstract

Viral load monitoring for hepatitis C virus (HCV) is necessary to diagnose infection and monitor response to therapy, but the tests involved are currently confined to specialist institutions. There is a need for a fast, accurate assay with limited operator input to enhance the access to viral load monitoring. We evaluated the quantification of HCV RNA in serum and plasma by the Cepheid Xpert HCV Viral Load assay in comparison to the Abbott RealTime HCV assay. Serum and plasma samples were gathered from HCV-infected individuals at four international sites. These were tested with the Xpert HCV Viral Load assay, and results were compared to quantification by the Abbott RealTime HCV assay. An external quality assessment panel of eight samples was also tested. In total, 614 samples were analyzed in the study, and the qualitative results agreed on the two platforms for 588 (95.8%) samples. Further analysis of 396 samples quantified by both tests showed strong correlation (correlation coefficient r = 0.99) across the quantifiable range, with Bland-Altman plot data showing a mean difference (±1.96 standard deviation) of 0.03 ± 0.44 log10 IU/ml. In the external quality assessment panel, the Xpert HCV Viral Load assay results (quantified in log10 IU per milliliter) were within 1 standard deviation of the target value for all but one sample, which was also similarly misquantified by the Abbott RealTime HCV assay. The Xpert HCV Viral Load assay performs well compared to a market-leading HCV viral load test and should be considered for instances where rapid near-to-patient testing is required.

Keywords: HCV RNA; hepatitis C virus; viral load.

Copyright © 2017 American Society for Microbiology.

Figures

FIG 1

Deming regression and Bland-Altman plot analysis of HCV quantification by the Abbott RealTime HCV and Xpert HCV Viral Load assays. (A) Deming regression of 396 samples quantified by both assays. (B) Bland-Altman plot of 396 samples quantified by both assays. (C) Deming regression of 92 HCV genotype 1 samples quantified by both assays. (D) Bland-Altman plot of 92 HCV genotype 1 samples quantified by both assays. (E) Deming regression of 51 HCV genotype 3 samples quantified by both assays. (F) Bland-Altman plot of 51 HCV genotype 3 samples quantified by both assays. The Deming regression plot shows the identity line (dashed line) and the Deming fit with a 95% confidence interval (black line and two dotted lines, respectively). The Bland-Altman plot shows the difference between the two assays in HCV quantification results plotted as a function of the mean of the two; the mean difference is highlighted by the black line, and dotted lines indicate ± 1.96 standard deviation.