Performance assessment of the new Xpert® HIV-1 viral load XC assay for quantification of HIV-1 viral loads

Background: HIV-1 RNA quantification is a key component of treatment monitoring. Objectives: To assess the performance of a redesigned HIV-1 RNA quantitative assay that uses a dual-target approach: Xpert (R) HIV-1 Viral Load (VL) XC. Study design: Fresh and frozen samples (N = 533) from HIV-1 positive patients tested with Abbott HIV-1 assays (Alinity m and RealTime [m2000]) were retested using the new Xpert XC assay. Three samples with known underquantification using the previous single-target Xpert assay were retested. Results: The Xpert XC assay yielded valid results in 98.5% (N = 528/536) of cases and showed high sensitivity in 80 fresh samples that had undetectable VLs or <= 1.7 log copies/mL with Alinity m. Linear regression and Bland-Altman analyses showed high concordance with the Abbott tests for quantified samples over a wide VL range (1.6-6.9 copies/mL), including non-B subtypes (mean difference=-0.1 +/- 0.23 log copies/mL). Mutations associated with integrase resistance did not impact the results. Very good linearity and reproducibility was shown for the tested subtypes B, CRF06_cpx, and CRF02_AG. Xpert XC VLs in samples that were previously underquantified using the original single-target Xpert assay were similar to those detected by the Abbott assays (+/- 0.11 log copies/mL). Conclusions: The Xpert XC assay showed excellent correlation with the Abbott assays for all tested HIV-1 subtypes. Sensitivity, linearity and accuracy were high in the therapeutically relevant VL range. With a time to result of only 90 min, this on-demand decentralized assay is a safe, reliable and fast option for VL monitoring in HIV-1-infected patients.

Automated summary

This study evaluated the performance of a redesigned HIV-1 RNA quantitative assay. The results demonstrated high sensitivity, good linearity, and accuracy of this assay in HIV-1 positive patients of different subtypes. Additionally, the assay showed simplicity and fast turnaround time.