The purpose of this study is to understand the effects of testosterone or estradiol on kidney function in transgender adolescents and young adults.

Inclusion Criteria:

• Identify as transgender
• Age 17-30 years (inclusive)
• Plan to start gender affirming hormone therapy (testosterone or estradiol) clinically in ≤ 1 months and remain on for at least 3 months

Exclusion Criteria:

• Cognitive, psychiatric or physical impairment resulting in inability to tolerate the study procedures (e.g. intellectual disability, schizophrenia, hallucinations)
• Type 1 or Type 2 diabetes
• Chronic kidney disease, or eGFR <60ml/min/1.73m2 by CKD-EPI formulation
• Uncontrolled hypertension (resting BP ≥ 140/90 mm/Hg)
• Allergy to shellfish, iodine or iohexol
• Currently taking: sulfonamides, procaine, thiazolesulfone and probenecid (renal clearance measurements of PAH cannot be made accurately if individuals are on these medications)
• Prior gender affirming hormone therapy use
• Prior gonadectomy
• Pregnancy

20 transgender youth and young adults (10 transgender females, 10 transgender males) before and 3 months after initiation of gender affirming hormone therapy to determine the impact of gender affirming hormone therapy on intrarenal hemodynamic function and tubular function.