Using a rapid urine tenofovir (TFV) test may improve adherence counseling for PrEP/ART, but traditional lateral flow assays (LFAs) provide only limited qualitative results. We developed a new urine TFV LFA that produces both semi- and fully-quantitative results. The study aim was to characterize the quantitative LFA results of urine TFV and their relationship with time since last dosing using samples from a controlled pharmacokinetic trial.
We conducted a three-arm, randomized study among HIV-negative adults receiving 300 mg tenofovir disoproxil fumarate (TDF) and 200 mg emtricitabine (FTC) over a six-week directly-observed therapy (DOT) phase and four-week washout phase. Urine samples from known timepoints since last drug ingestion were tested using the rapid LFA assay. Using the same color intensity reference card, on a scale of 0-5, independent visual assessment from two lab technicians were averaged as one semi-quantitative result. LFA strips were also read within 10 minutes of test completion using an optical reader that gave fully-quantitative readings. We calculated the Spearman coefficients between LFA results and time since last dosing. We also evaluated the performance of using different cutoffs of LFA results to correctly categorize samples with different time since last dosing.
Twenty-eight adults with 268 spot urine samples were included in this analysis. The presence of TFV resulted in no or light color signal on the LFA strip, and thus lower values of LFA results. Both semi- (averaged visual scores) and fully- (optical reader readings) quantitative LFA results increased with longer time since last dosing. The correlation coefficients between time since last dosing and averaged visual scores and optical reader readings were 0.80, and 0.83, respectively. An averaged visual score above 1.5 or an optical reading over 1500 had correctly identified all samples if their last dose was ingested more than 24 hours ago. No samples with an averaged visual score above 2.5 or an optical reading over 3000 were from participants who took their last dose within the past 48 hours.
Both averaged visual scores and optical reader readings were highly correlated with time since last dosing. Benchmarks from this study will help guide and promote future adoption of LFA as a low-cost and easy-to-perform point-of-care (POC) test for PrEP/ART adherence monitoring and interventions.
