Serum Hormone Concentrations in Transgender Youth Receiving Estradiol

This study aimed to evaluate the serum estradiol levels in gender-diverse youth to compare the efficacy of different estradiol routes in achieving therapeutic blood levels and suppressing serum testosterone levels.

This was a retrospective chart review of patients who initiated estradiol at an adolescent gender clinic between 2010 and 2019. Data on the route of estradiol administration and antiandrogen use (spironolactone or gonadotropin-releasing hormone agonist) were collected, and laboratory data were analyzed. Scatterplots were used to visualize the relationship between the estradiol dose and testosterone and estradiol laboratory values.

A total of 118 patients were included, with a mean (standard deviation [SD]) age of 17.2 (1.6) years. The most common route of estradiol administration was oral only (62.7%), followed by transdermal only (23.7%), multiple routes excluding subcutaneous (8.5%), and any subcutaneous (5.1%). Notable variability was observed in the serum estradiol levels, with means (SDs) of 131.9 (120.4) pg/mL for those on oral estrogen 6 to 8 mg per day, 62.6 (40.3) pg/mL for those on transdermal estrogen 0.1 to 0.15 mg every 24 hours, and 53.6 (42.4) pg/mL for those on subcutaneous estradiol. In patients who received spironolactone, transdermal estradiol was associated with lower testosterone levels than estradiol administered orally or subcutaneously.

Oral, transdermal, and subcutaneous administrations of estrogen all lead to increased serum estradiol levels and are effective for use in gender-affirming care for youth. Patients on transdermal estrogen tended to have lower serum estradiol levels but also had more suppression of serum testosterone levels.