Testosterone Levels in Transgender Women Undergoing Gender-Affirming Hormone Therapy.

The participation of transgender women in women's sports is a topic rife with controversy and lacks a unified set of guidelines. Testosterone thresholds vary widely between organizations, ranging from less than 2.5 nmol/L to less than 10 nmol/L during a pre-competition period of 12 to 24 months. Little is known about how quickly and to what degree testosterone is suppressed below the thresholds required for participation in women's sports after the initiation of gender-affirming hormone therapy (GAHT). This study examined trends in testosterone levels among transgender women undergoing the current standard of care GAHT and compared these values to existing guidelines for participation in women's sports. After 12 months on GAHT, the median testosterone level was 0.52 nmol/L (95% CI: 0.47-0.73), and the mean was 3.39 nmol/L (95% CI: 2.63-4.15) (N=261). After 24 months, the median testosterone level was 0.43 nmol/L (95% CI: 0.35-0.66), and the mean was 3.90 nmol/L (95% CI: 2.51-5.29) (N=112). These results suggest substantial variability in testosterone levels among transgender women on GAHT. These data may inform the typical course of testosterone suppression under the current standard of care and serve as a reference for future athlete-specific studies. Further research is needed to better understand both the extent of testosterone suppression across different GAHT regimens and the duration required to meet eligibility guidelines for participation in women's sports.