By Mila Madison

Appearing in the journal Endocrine Practice, the new study is the first to investigate the effectiveness of current treatments used in The United States that are aimed at reaching targeted and sustained levels of testosterone in transgender women over a period of several years. The purpose of the cross-sectional study was to assess the testosterone suppression achieved with spironolactone and estrogens.

Testosterone and estradiol levels were extracted using the electronic medical records of 98 anonymized transgender women who were treated with oral spironolactone and oral estrogen therapy at the Endocrinology Clinic at Boston Medical Center. Patients were divided into four similarly sized groups using the average estradiol dose they were administered over the course of their treatment. Current Endocrine Society guidelines suggest that patients should reach a serum testosterone <50ng/dl.

Only a quarter of transgender women taking the spironolactone and estrogen regimen were able to lower their testosterone levels within the usual female physiologic range. Another quarter could not achieve ideal female levels, but they remained below the male range virtually all of the time. One quarter of the women were unable to achieve any significant suppression of their testosterone levels.

Patients required an average of 9 months to reach steady testosterone levels overall, though the levels obtained varied from patient to patient.

Those who had a normal BMI (Body Mass Index) had higher testosterone while patients who had an obese BMI displayed lower testosterone levels throughout their treatment.

The age of the patient had no significant effect on testosterone levels.

"This study allowed us to identify patients who achieved differing levels of testosterone suppression, including a group of patients unable to achieve any significant testosterone suppression. These patients may have had difficulty adhering to their treatment or may have had a different physiologic response to treatment than other patients. On the other hand, patients who were able to achieve high levels of suppression may have adhered stringently to their treatment or had robust response based on physiology," explained corresponding author Joshua D. Safer, MD, FACP, associate professor of medicine at Boston University School of Medicine. "Also, it is not known if there is an absolute need for all transgender women to suppress the testosterone levels entirely into the female range. Perhaps it is acceptable for some to have levels just above the usual female upper limit."

The researchers believe future studies could pinpoint specific characteristics of patients who fall into each quartile of average steady state testosterone. "Identification of reasons why certain patients have better testosterone suppression could help improve anti-androgen therapy and allow for targeted interventions to advance the U.S. medical regimen for transgender women. As well, future study could determine the specific impact of testosterone at different levels even if not entirely in the female range," said Safer, who is also the Medical Director of the Center for Transgender Medicine and Surgery at Boston Medical Center.