Hormonal Target Validation based on Biochemical Shifts in Gender-Affirming Hormone Therapy

Background: Hormonal targets for gender-affirming hormone therapy (GAHT) remain largely unvalidated in gender-diverse individuals, with no clinical markers to assess dosing adequacy. We hypothesize that a biochemical shift towards the hormonal profile of the identified sex correlates with appropriate dosing. Methods: A data-subset from the National Health and Nutrition Examination Survey (NHANES), comprising 5433 assumed-cisgender individuals (47.2% male) aged <52 years, was used to train and validate a Random Forest model to predict sex-assigned-at-birth, incorporating platelet count, HDL%, SHBG, creatinine, and hematocrit. Being assigned-female-at-birth was weighted at 0.54. The model was subsequently run in 171 transgender men (TM) and 119 transgender women (TW) from the European Network for the Investigation of Gender Incongruence (ENIGI) Ghent cohort. Blood samples were collected at 0, 3, 12, 18, 24 and 36 months after GAHT-initiation. Hormonal profiles were compared based on predicted sex-assigned-at-birth. Results: The model achieved 91% accuracy in NHANES, with baseline accuracy of 81% in ENIGI, declining to 11% at 36 months. Median E2 levels in TW predicted male-assigned-at-birth (62.5pg/mL, IQR: 40.9-77.1) were significantly lower (p<0.0001) than in TW predicted female-assigned-at-birth (81.2pg/mL, IQR: 64.9-102.0). Difference in T-levels in TM classified female-assigned-at-birth and predicted male-assigned-at-birth did not reach significance. Classification according to sex-at-birth seemed less likely to occur at higher E2 levels in TW. Conclusion: The innate sexual dimorphism of biochemical parameters might provide a framework for GAHT target validation. Significantly different hormonal profiles can be seen in people depending on the biochemical shift experienced during GAHT.