Biochemical Changes During the First Year of Feminizing Hormone Therapy in Transfeminine Individuals

BACKGROUND: Persons with assigned male sex at birth (AMAB) might wish to obtain feminization and/or demasculinization according to the person's gender identity and are therefore treated with estradiol and/or antiandrogens. AIM: The aim was to evaluate biochemical changes and side effects in AMAB individuals treated with guideline-based feminizing hormone treatment (FHT). METHODS: Medical charts of 99 AMAB individuals ≥ 18 years referred to the Center for Gender Identity; Aalborg University hospital, Denmark, between January 2017 and July 2019 were reviewed to identify adverse side effects. Furthermore, data from the laboratory information system (Labka II) were retrieved to obtain biochemical parameters. Biochemical plasma concentrations after initiation of FHT were compared to concentrations prior to FHT and to existing guidelines. OUTCOMES: After 11–19 months, 29% of the trans feminine individuals had plasma estradiol concentrations within the treatment target. RESULTS: The plasma concentration of estradiol varies greatly during FHT. Plasma levels of estrogen were within the treatment target after 11–19 months of treatment, whereas 100% had concentrations within the reference range for premenopausal cis-women. Furthermore, plasma concentrations of lipids and hematological parameters approached female reference ranges after 11 months of FHT. CLINICAL IMPLICATIONS: The target levels of plasma estradiol concentrations during FHT could be expanded, making the wanted physiological changes easier to obtain. STRENGTHS & LIMITATION: This cohort study included 99 AMAB individuals and biochemical evaluation was possible in 67 individuals. Only one individual was lost during follow-up. However, the follow-up period was limited making evaluation of long-term side effects impossible. CONCLUSION: Plasma concentration of estradiol varies greatly during guideline based FHT, making plasma estradiol levels within the target level difficult to attain. JA Hojbjerg, AD Højgaard, A-M Hvas. Biochemical Changes During the First Year of Feminizing Hormone Therapy in Transfeminine Individuals. Sex Med 2021;10:100472.