A comparison of plasma efavirenz and tenofovir, dried blood spot tenofovir-diphosphate, and self-reported adherence to predict virologic suppression among South African women.

BACKGROUND: Tenofovir-diphosphate (TFV-DP) in dried blood spots (DBS) is an objective long-term adherence measure but data are limited on its ability to predict virologic suppression (VS) in people on antiretroviral (ARV) treatment. There are also no data comparing DBS TFV-DP with plasma ARV concentrations as predictors of VS.

METHODS: Women who were on a first-line regimen of tenofovir, emtricitabine, and efavirenz (EFV) were enrolled in a cross-sectional study. Plasma EFV and tenofovir (TFV), DBS TFV-DP assays, and 30-day self-reported adherence were evaluated as predictors of VS (<50 copies/mL) with area under the curve (AUC) of receiver operating characteristics (ROC) and logistic regression.

RESULTS: We enrolled 137 women; mean age 33 years; median 4 years on ART; 88 (64%) had VS. In ROC analyses: DBS TFV-DP (0.926 [95%CI 0.876-0.976]) had a higher AUC than plasma TFV (0.864 [0.797-0.932]; p=0.006), while plasma EFV (0.903 [0.839-0.967]) was not significantly different from DBS TFV-DP (p=0.138) or plasma TFV (p=0.140); all ARV assays performed better than self-report. The association of TFV-DP in DBS with VS strengthened with increasing concentrations (reference <350 fmol/punch: 350-699 fmol/punch aOR 37 [8-178]; 700-1249 fmol/punch aOR 47 [13-175]; ≥1250 fmol/punch aOR 175 [20-1539]). "White coat adherence" (defined as DBS TFV-DP <350 fmol/punch with detectable plasma TFV) was only detected in 4 women.

CONCLUSIONS: Plasma EFV, TFV and DBS TFV-DP were all strong predictors of VS. EFV or TFV assays have potential for development as point-of-care assays for use as objective adherence measures in resource-limited settings.