Testosterone Levels Achieved by Medically Treated Transgender Women in a United States Endocrinology Clinic Cohort

Abstract

Most transgender women depend on medical treatment alone to lower testosterone levels in order to align physical appearance with gender identity. The medical regimen in the United States typically includes spironolactone and estrogens. The purpose of this cross-sectional study was to assess the testosterone suppression achieved among transgender women treated with spironolactone and estrogens. Testosterone and estradiol levels were extracted from the electronic medical records of 98 anonymized transgender women treated with oral spironolactone and oral estrogen therapy at the Endocrinology Clinic at Boston Medical Center. Patients starting therapy required about 9 months to reach a steady-state testosterone, with significant heterogeneity of levels achieved among patients. Patients with normal body mass index (BMI) had higher testosterone levels, whereas patients with obese BMI had lower testosterone levels throughout treatment. Stratification of patients by age or spironolactone dosage revealed no significant difference in testosterone levels achieved. At steady state, patients in the highest suppressing quartile were able to achieve testosterone levels of 27 ng/dL, with a standard deviation of 21 ng/dL. Measured serum estradiol levels did not change over time and did not correlate with dosage of estradiol administered. Among a cohort of transgender women treated with spironolactone and estrogen, the highest suppressing quartile could reliably achieve testosterone levels in the female range at virtually all times. The second highest suppressing quartile could not achieve female levels but remained below the male range virtually all of the time. One quartile was unable to achieve any significant suppression. BMC = Boston Medical Center BMI = body mass index CPY = cyproterone acetate LC-MS/MS = liquid chromatography-tandem mass spectrometry Q = quartile.