Testosterone Levels Among Transgender Women on Gender-Affirming Hormone Therapy

Background and/or Objectives: Little is known regarding duration of gender-affirming hormone therapy (GAHT) required to suppress testosterone within the range required for participation in women’s sport, often less than 2.5 or 5 nmol/L. This study aimed to elucidate trends in testosterone levels among transgender women on GAHT.

Design: Retrospective cohort study

Setting : Academic hospital system.

Participants : Participants included in our retrospective chart review were seen between 2003-2023 with record of at least one ICD9/10 diagnosis code associated with transgender individuals. We included patients on combined estradiol and spironolactone who had testosterone lab values in our electronic medical record obtained after starting GAHT.

Interventions: Standard of care GAHT therapy.

Main Outcome Measures: Mean testosterone values were calculated.

Results: A total of 261 patients met study criteria. Patients’ mean testosterone level on initial testing after starting GAHT was 6.04 nmol/L (95% CI [5.57, 6.51]). After 12 months on GAHT, the 261 patients demonstrated a mean testosterone level of 3.39 nmol/L (95% CI [3.00,3.78]). After 24 months, 112 patients had testosterone levels drawn with a mean level of 3.90 nmol/L (95% CI [3.19,4.61]). At initial testing, 37.2% of patients had higher testosterone values than the 5 nmol/L threshold, while 48.3% were higher than the 2.5 nmol/L threshold. At one year, 19.5% and 23.8% were above the respective thresholds, while 22.3% and 25.0% were above at two years.

Conclusions: Many organizations have testosterone-based policies restricting sports participation of transgender women. Policies vary in testosterone threshold and length of testosterone suppression. Testosterone levels less than 5 nmol/L or 2.5 nmol/L are required by many organizations. These data suggest that there is a wide variability in testosterone levels, and a large percentage of patients still have supra-threshold values at one and two years. Further understanding of duration of GAHT and degree of endogenous hormone suppression required to meet guidelines for participation in women’s sport is needed.