Abstract Body

Therapeutic drug monitoring measures adherence to tenofovir (TFV)-based PrEP more accurately than self-report but has not been available at the point-of-care (POC) until now. We developed an ELISA using a highly-selective antibody to TFV in urine and previously validated it against spectrometry-based methods with high accuracy. We have now developed a lateral flow immunoassay (LFA) using this antibody, which permits testing at the POC. A cut-off for the LFA of 1,500 ng/ml was previously selected from a directly observed therapy study to accurately classify recent dosing. The objective of this analysis was to compare a novel POC test for PrEP to laboratory-based ELISA in diverse patient populations.

Urine samples were analyzed using the ELISA and POC LFA test from two cohorts of PrEP users taking tenofovir disoproxil fumarate/emtricitabine: the Partners PrEP Study, which recruited heterosexual men and women, and the IBrEATHe Study, which recruited transwomen using estrogen and transmen using testosterone hormone therapy. We calculated the sensitivity and specificity of the POC test compared to laboratory-based ELISA at a cut-off of 1,500 ng/ml.

Overall, 684 urine samples were tested from 324 participants in the two cohorts. In Partners PrEP, 454 samples from 278 participants (41% cisgender women) were tested; the median age was 33 years (interquartile range [QR] of 28-39). In IBrEATHe, 231 samples from 46 individuals (50% transwomen) were tested; the median age was 31 (IQR 25-40). Overall, of the 505 samples with tenofovir (TFV) levels greater than or equal to the cut-off using lab-based ELISA, 505 of the POC test results were also positive, yielding 100% sensitivity. Of the 179 samples with TFV levels below the cut-off, 178 were negative with the POC test, yielding 99.4% specificity. The accuracy of the POC LFA was 99.8% compared to ELISA.

In 324 women and men (both cisgender and transgender) taking PrEP, the sensitivity, specificity, and accuracy of a novel POC test for urine TFV all exceeded 99% when compared to a lab-based ELISA method. Given the association of low urine TFV levels with HIV seroconversion events, the simplicity of using the LFA, and its expected low cost, this POC test is a promising tool to support adherence to PrEP that could be widely scalable to real-world clinical settings. Adherence support using this POC test should be evaluated in a randomized controlled trial.