The Role of Body Composition Assessment in Tailoring Gender-Affirming Treatment for Transgender/Gender Diverse Youth.

Purpose: We explored the relationship between body composition parameters and achieved hormone levels in transgender/gender diverse (TGD) adolescents on gender-affirming hormones. Methods: This retrospective study was conducted between January 2018 and January 2023 and included 159 TGD adolescents (109 TGD males) aged ≤21 years and treated with gender-affirming hormones. Body composition was assessed by bioelectrical impedance analysis. Anthropometric measurements, treatment dose, and hormone levels were extracted from medical files. The outcome measures were estradiol and testosterone levels in correlation with indices of adiposity and muscle adjusted for treatment dose and duration. Results: Peak testosterone blood levels, adjusted for dose and treatment duration, correlated negatively with body mass index z-score (r = -0.541, p < 0.001), fat mass (r = -0.454, p = 0.004), truncal fat mass (r = -0.444, p = 0.005), appendicular skeletal muscle mass (r = -0.660, p < 0.001), skeletal muscle mass index (r = -0.566, p < 0.001), body surface area (BSA; r = -0.620, p < 0.001), and estimated basal metabolic rate (r = -0.658, p < 0.001). Trough testosterone blood levels, adjusted for dose and treatment duration, correlated but to a lesser extent with muscle indices and BSA. Estradiol levels in TGD females did not correlate significantly with body composition parameters. Conclusion: Our results demonstrate an association between both adipose and muscle mass and testosterone levels. This is of special importance, as TGD youth exhibit a higher frequency of differing weight status and body composition. These findings enable a more individualized approach to medication dosing for TGD adolescents. Body surface area may be a potential indicator for determining the appropriate testosterone dose in cases where data on body composition are unavailable.