Urine Test Shows Predictive Values for PrEP Adherence

In a recent study presented at the Conference on Retroviruses and Opportunistic Infections 2023 in Seattle, WA, researchers calculated the predictive values of urine point-of-care tenofovir (POC-TFV) tests, self-reported recent pre-exposure prophylaxis (PrEP) use, and TFV-diphosphate (TFV-DP) in dried blood spots.

Although the accuracy of self-reported PrEP use can be called into question at times, self-reporting is one of the most frequently used reporting methodologies in research. Considering the suboptimal metrics associated with self-reporting PrEP adherence, the authors of the current study set out to determine whether urine POC-TFV could be used as an alternative approach.

The authors found that “the urine POC-TFV assay had excellent predictive values for adherence in a real-world cohort, while self-reported adherence did not add significantly to prediction.”

For the study, researchers invited participants who were current PrEP users in the RADAR community-cohort study of young men and transgender women who have sex with men. During three monthly visits, participants completed a survey of daily PrEP use in the prior 7 days and provided dried blood spot and urine samples. The researchers tested dried blood spot samples for TFV-DP to estimate the average dosing over the prior month and emtricitabine-triphosphate (FTC-TP) to assess recent dosing, which was defined here as the past 2 to 3 days. A urine POC-TFV test was performed to determine recent adherence, which was defined here as  the past 4 to 7 days.

In a subset of 73 PrEP-users who contributed 126 observations, self-reported adherence was over-reported (87% for four or more doses in last 7 days), compared with urine TFV (69%), DBS FTC-TP (68%), and DBS TFV-DP (67%). Although self-reporting overestimated longer-term adherence, it had better results for short-term adherence metrics. And in multivariable logistic regression analyses, the urine assay was a significant predictor of dried blood spot TFV-DP (OR = 30.2, p < .0001). The study results also showed that self-reporting did not add significantly to prediction.

Considering the results of the study, plus the overall cost effectiveness associated with urine POC-TFV, the test may be useful as an adherence assay moving forward.

“The POC assay provides results in several minutes to enable same-visit counseling and intervention, requires no specialized training, and is projected to be low-cost,” the authors concluded. “It could also be used for research where objective short term adherence metrics are needed.”

Reference:

Mustansk B, D'Aquila R, Gandhi M, Ryan D, Spinelli MA, Newcomb M. Urine point-of-care TFV test shows strong predictive clinical and research utility. Presented at: Conference on Retroviruses and Opportunistic Infections (CROI); February 19-22, 2023; Seattle, WA. Accessed March 3, 2023. https://www.croiconference.org/abstract/predictive-values-of-urine-prep-tfv-test-show-strong-clinical-and-research-utility/.