We examined the relationship between urine tenofovir
(TFV) levels measured with a novel immunoassay
, which permits point-of-care
testing, with HIV seroconversion and objective adherence metrics in a large preexposure prophylaxis
(PrEP) demonstration project.
Secondary analysis of stored specimens from an open-label PrEP cohort study.
We examined the association between undetectable urine
TFV levels and HIV seroconversion in iPrEx open-label extension using generalized estimating equations. We examined rank correlations between levels of TFV and emtricitabine in urine
, dried blood spots (DBS), and hair and determined the sensitivity and specificity of undetectable urine
TFV for predicting dosing cut-offs in DBS.
The median urinary TFV level was 15 000 ng/ml in those who remained HIV-negative (n
= 105; interquartile range: 1000–45 000); 5500 in those who eventually seroconverted (n
= 11; interquartile range: 1000–12 500); and all were undetectable at seroconversion (n
= 9; P
< 0.001). Decreasing strata of urine
TFV levels were associated with future HIV seroconversion (P
= 0.03). An undetectable urine
TFV was 100% sensitive and 81% specific when compared with an undetectable DBS TFV-diphosphate level and 69% sensitive, but 94% specific when compared with low adherence by DBS (<2 doses/week).
TFV detection by a novel antibody-based assay was associated with protection from HIV acquisition among individuals on PrEP. Urine
TFV levels were correlated with hair and DBS levels and undetectable urine
TFV was 100% sensitive in detecting nonadherence. By implementing the immunoassay
into a point-of-care
strip test, PrEP nonadherence could be detected in real-time, allowing rapid intervention.