Will use a subset of the main study cohort of transgender or non-binary individuals to evaluate the relationships between self-reported exogenous hormone use, endogenous hormone values, renal biomarkers, drug levels and directly measured renal function.

This cross-sectional sub-study will use a subset of the main study cohort of transgender (TG) or non-binary (NB) individuals to evaluate the relationships between self-reported exogenous hormone use, endogenous hormone values (serum estradiol, estrone, free/total testosterone), renal biomarkers, drug levels (measured by tenofovir diphosphate, TFV-DP, and emtricitabine triphosphate, FTC-TP, on dried blood spot cards and urine) and directly measured renal function (iohexol clearance).

Inclusion Criteria:

• HIV-uninfected
• Identifying as transgender or nonbinary (TG/NB)
• Age ≥ 18 years (adult)
• At risk of acquiring HIV
• Calculated creatinine clearance (CRCL) ≥ 60 mL/minute
• Taking emtricitabine/tenofovir alafenamide
• Willing to receive a small dose of iohexol
• Willing to provide 30 mL blood and a urine sample

Exclusion Criteria:

• Allergy to iohexol
• Use of concurrent medications that may interfere with iohexol such as metformin, amiodarone or beta-blockers
• Anuric or unable to produce 30 mL of urine
• Other condition that, in the opinion of the investigator, would put the participant at risk, complicate interpretation of study outcome data, or would otherwise interfere with participation or achieving the study objectives