OBJECTIVE: 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.
METHODS: 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.
RESULTS: 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.
CONCLUSION: 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.
