Comparison between Roche and Xpert in HIV-1 RNA quantitation: A high concordance between the two techniques except for a CRF02_AG subtype variant with high viral load titters detected by Roche but undetected by Xpert

- Evaluation of Cepheid Xpert HIV-1 viral load.
- Comparison between Roche and Xpert in HIV-1 viral load quantitation.
- An HIV-1 CRF02_AG subtype variant detected by Roche but not detected by Xpert.
- Use of the Cepheid Xpert HIV-1 viral load assay in the clinical HIV laboratory.

BackgroundHIV-1 viral load (VL) testing is important to predict viral progression and to monitor the response to antiretroviral therapy. New HIV-1 VL tests are continuously introduced to the market. Their performance is usually compared to Abbott and/or Roche HIV-1 VL assays, as reference. The Xpert HIV-1 VL test was recently introduced, but its performance compared to Roche has not been sufficiently studied.ObjectivesTo compare the Xpert assay with Roche and to assess its use in the HIV clinical laboratory.Study designA total of 383 plasma samples of HIV-1 infected patients previously tested by Roche, were retrospectively tested by Xpert to determine concordance between the two assays. Samples included a diversity of HIV-1 subtypes and a wide range of VLs.ResultsThere was a high concordance between the two assays, except for a CRF02_AG subtype variant with high VL titters, that was detected by Roche but undetected by Xpert. The 5′ long terminal repeat gene region of this virus, targeted by the Xpert assay, was amplified and sequenced. A 25 nucleotide insert was identified, but was unmatched to any known sequences of HIV-1. This particular insert, however could not explain the false-negativity by the Xpert assay.ConclusionsThis study underlines the challenge to routine VL testing due to the high genetic diversity of HIV-1. Clinicians should, therefore be advised that a negative VL in cases where the clinical picture does not match the laboratory report, might in fact be, a false-negative result of the VL assay.