SUN-039 Estradiol Dose and Concentrations in Transfeminine Individuals

Background: Feminizing hormone therapy with estradiol is used to align an individual’s physical characteristics with their gender identity. Australian expert consensus guidelines (1) recommend targeting estradiol concentrations of 250-600 pmol/L (68-163 pg/mL) based on local cross-sectional data (2). We aimed to establish the proportion of individuals achieving estradiol concentrations in consensus guidelines. Methods: A retrospective cross-sectional analysis was performed of transfeminine individuals attending a primary or secondary care clinic in Melbourne, Australia who were prescribed oral estradiol valerate for at least 6 months and had estradiol dose and concentration available. Estradiol concentration was measured by immunoassay. Outcomes were (1) proportion of individuals achieving target estradiol concentrations and (2) influence of estradiol dose and BMI on estradiol concentrations. Results: 259 individuals (median age 25.8(IQR 21.9,33.5) years)) had data available for analysis. Median duration of estradiol therapy was 24(15,33) months. Median estradiol concentration was 328(238,434) pmol/L (89(65,118) pg/mL) on 6(4,8) mg estradiol valerate. 172 (66%) individuals had estradiol concentrations within the target range recommended in consensus guidelines. 70 (27%) individuals had estradiol concentrations below target, and 17 (7%) above target. There was a weak positive correlation between estradiol dose and estradiol concentration (r=0.156, p=0.012). There was no correlation between BMI and estradiol concentration achieved (r=-0.063, p=0.413). Conclusions: 66% of individuals achieved estradiol concentration recommended in consensus guidelines with a relatively high oral estradiol dose. There was significant interindividual variability. Estradiol concentration should be interpreted in conjunction with clinical features of feminization and weighed against potential risks of escalating estradiol dose. References 1. Cheung AS, Wynne K, Erasmus J, Murray S, Zajac JD. Position statement on the hormonal management of adult transgender and gender diverse individuals. Med J Aust 2019; 211:127-133 2. Angus L, Leemaqz SY, Ooi O, Cundill P, Silberstein N, Locke P, Zajac JD, Cheung AS. Cyproterone acetate or spironolactone in lowering testosterone concentrations for transgender individuals receiving estradiol therapy. Endocr Connect 2019