Methods: 50 aliquots of diluted WHO HIV standard at viral loads <200 c/mL and 4-6 aliquots of plasma samples from 4 patients experiencing blips of 50-200 c/mL after having had HIV-1 RNA <50 c/mL were quantified using the Cobas AmpliPrep/Cobas TaqMan v2.0 HIV-1 assay (Roche) at Covance central laboratories.
Results: The TaqMan assay of the WHO standards at viral loads <200 c/mL performed within the expected variability according to assay specifications. However, standards with 36 c/mL and 17 c/mL of HIV-1 RNA showed values of ≥50 c/mL in 66% and 18% of tests, respectively. In patients treated with antiretrovirals and having unexpected ≥50 c/mL results, retesting of multiple aliquots of stored plasma found <50 c/mL in most cases upon retesting (15/16; 94%).
Conclusion: HIV-1 RNA assays have expected variability around 50 c/mL that affect clinical trial results and clinical practice. In patients with a history of viral load suppression, unexpected low-level viremia may be due to assay variability rather than poor drug adherence or true virologic failure. Retesting a stored aliquot of the same sample may differentiate between assay variability and virologic failure as the source of perceived viremia. This retesting strategy could save time, money, and anxiety for patients and their providers, and decrease follow-up clinic visits without increasing the risk of virologic failure and resistance development.
J. Eron, Jr.,
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