The correlation between single copy plasma HIV-1 RNA assays (research tests) and less sensitive but automated, FDA-cleared plasma HIV-1 RNA assays is not well-defined. We examined this association by testing plasma with both a single copy qRT-PCR assay and the Abbott M2000 automated, commercial platform.
The single copy qRT-PCR assay targeting integrase (iSCA) was performed as published (Cillo, J Clin Micro 2016) with a limit of detection (LoD) 0.4 cp/mL for a 5 mL sample tested. iSCA results were classified as HIV-1 RNA ‘detected’ or ‘not detected’. The FDA-cleared Abbott M2000 RealTime HIV-1 Viral Load assay has a LoD of 40 cp/mL for a 1.0 mL sample. Results below 40 cp/mL were reported as either <40 cp/mL detected but not quantifiable (<40 target detected) or target not detected (TND). Plasma samples obtained at entry into the ACTG A5321 cohort study were tested with both assays. Participants were on suppressive ART with HIV RNA <40 cp/mL by the Abbott assay.
Participants are mostly men (82%), median age of 49, and median of 7 years on ART. Paired samples from 309 participants were tested with both assays. 52% of iSCA results had undetectable HIV-1 RNA; the undetectable iSCA results were primarily (94%) <0.4 cp/mL; nine were <0.5 to <1.1 cp/mL because of lower sample volume. By Abbott M2000, 17% of samples were <40 target detected and 83% were TND. Of the samples TND by Abbott, 43% had HIV-1 RNA detected by iSCA. Of the samples <40 target detected by Abbott, 73% had detectable HIV-1 RNA by iSCA (Figure; p<0.001). Results were similar excluding nine with lower iSCA plasma volume, categorizing iSCA as <0.4 vs. ≥0.4 cp/mL: 44% ≥0.4 cp/mL if TND by Abbott and 73% ≥0.4 cp/mL if target detected (p<0.001).
73% of plasma samples with an Abbott HIV-1 RNA result of <40 cp/mL target detected also had HIV-1 RNA detected by iSCA, whereas 43% of samples that were TND by Abbott had HIV-1 RNA detected by iSCA. The difference between <40 cp/mL target detected and TND by Abbott has meaningful information, and can be used to estimate the likelihood of HIV-1 RNA detectability by iSCA. The strong association between the results of both assays indicates that a high-throughput automated assay such as Abbott M2000 could be used in epidemiologic investigations of low-level viremia and to screen for changes in low-level viremia following therapeutic interventions, thereby reducing the need for more labor-intensive research single copy assays.