C72-09 Pulmonary Function Tests in Transgender Adolescents Receiving Gender-Affirming Hormone Therapy

Rationale Sex hormones are known to influence lung development and function; however, the effects of Gender-Affirming Hormone Therapy (GAHT) on pulmonary physiology in Transgender and Gender Diverse (TGD) adolescents remain unclear. Spirometry interpretation is typically based on Sex Assigned at Birth (SAAB), yet its applicability in this population is debated. Our objective was to evaluate pulmonary function in TGD adolescents receiving GAHT and examine associations between serum hormone levels and lung function. Methods Cross-sectional study in a tertiary TGD clinic between March 2021 and April 2023. TGD males received Gonadotropin-Releasing Hormone Agonist (GnRHa) and testosterone; TGD females received GnRHa and estradiol. Lung function was assessed by body plethysmography and analysed according to both SAAB and gender identity. Additional variables included hormone levels, GAHT duration, smoking, chest binding, and surgical history. Results The cohort included 27 TGD males (mean age 17.7 ± 1.2 years) and 12 TGD females (mean age 19.1 ± 1.6 years), with median GAHT durations of 18.9 and 23.2 months, respectively. Absolute lung volumes remained within normal limits by SAAB reference equations. TGD females (assigned male at birth) had significantly higher mean Forced Expiratory Volume in 1 Second (FEV1) (3.6 ± 0.4 L vs. 3.1 ± 0.4 L, P < 0.001), Forced Vital Capacity (FVC) (3.9 ± 0.5 L vs. 3.4 ± 0.5 L, P = 0.001), and Total Lung Capacity (TLC) (5.4 ± 0.8 L vs. 4.4 ± 0.6 L, P < 0.001) than TGD males. %-predicted values differed when calculated by SAAB vs. gender identity. Follicle-Stimulating Hormone (FSH) levels correlated negatively with FVC in TGD females, while testosterone correlated positively with Residual Volume/Total Lung Capacity (RV/TLC). Conclusions Lung function remained physiologically aligned with SAAB despite GAHT, supporting continued use of SAAB-based reference equations for accurate interpretation of pulmonary function tests in TGD adolescents. Correlations with FSH and testosterone were identified. To the best of our knowledge, this is the first study to evaluate pulmonary function in this unique population using both SAAB- and gender-identity-based reference equations.