Concordance of HIV-1 RNA Values by Amplicor and TaqMan 2.0 in Patients With Confirmed Suppression in Clinical Trials

Background. The COBAS AMPLICOR HIV-1 MONITOR Test, version 1.5 (Amplicor) has been replaced with the COBAS AmpliPrep/COBAS TaqMan HIV-1 Test, version 2.0 (TaqMan 2.0), a real-time polymerase chain reaction human immunodeficiency virus type 1 (HIV-1) assay with higher sensitivity and broader dynamic range. HIV-1 RNA values at the 50 copies/mL cutoff drive major patient management decisions and clinical study outcomes. Methods. A total of 2217 samples were collected from 1922 HIV-1-infected subjects taking antiretroviral therapy for at least 48 weeks and had at least 2 consecutive samples with HIV-1 RNA < 50 copies/mL by Amplicor from 7 recent clinical trials. HIV-1 RNA results were obtained from the Amplicor and TaqMan 2.0 assays in parallel by a reference laboratory. Results. The overall concordance between assay results was 96% at the cutoff of 50 copies/mL. However, statistically significant discordance at the 50 copies/mL cutoff was found between the assays for 3.9% of samples (n = 87). By TaqMan 2.0, virologic failure defined as HIV-1 RNA = 50 copies/mL was reported for 2.8% more samples than Amplicor. Of these 87 samples, 68 samples fell within the predicted range of assay variability. Retesting of HIV-1 RNA by TaqMan 2.0 confirmed the discordance in only 28 of the 87 samples. Conclusions. The TaqMan 2.0 assay reports fewer subjects below the clinical endpoint of HIV-1 RNA < 50 copies/mL in HIV clinical trials than the Amplicor assay. This difference must be considered when assessing disease progression, designing clinical trials, and comparisons with historical trials that used the Amplicor assay.