Study Examines Risk of Blood Clots in U.S. Transgender Women

Transgender women undergoing cross-sex hormone therapy in the United States have a low incidence of venous thromboembolism (VTE), according to new research in the Journal of Sexual Medicine.

Many transgender individuals undergo cross-sex hormone therapy as they transition from their biological gender to the gender they identify with. The hormones help them develop the secondary sex characteristics of their preferred gender.

However, one concern for transgender women (transitioning from male to female) is VTE – a blood clot. Sometimes, VTE occurs in a deep vein, often in the leg. But the clot can also break away and block blood flow to the lungs. This is called a pulmonary embolism.

Protocols for cross-sex hormone therapy are different in Europe and the United States. Patients in both regions typically receive estradiol, a type of estrogen. In Europe, estradiol is usually paired with a progestin hormone called cyproterone acetate, which is not approved for use in the U.S. Instead, U.S. patients usually take estradiol along with an antiandrogen called spironolactone. (An antiandrogen works to suppress male hormones.)

Most of the research on VTE in cross-sex hormone therapy is based on the European protocol. In this study, researchers examined VTE incidence in transgender women being treated in the U.S.

They studied the medical charts of 676 transgender women who received cross-sex hormone therapy between 2008 and 2016. On average, the women were on hormone therapy for 1.9 years.

The researchers discovered that only one patient – 0.15% of the group – had a VTE (a pulmonary embolism) during this time. This rate was lower than the rates in European studies.

The study authors pointed out that the patients in this study took oral estradiol. The hormone can also be injected into a muscle or applied directly to the skin, and the VTE incidence rates for these methods are unclear.

The authors also recommended that future research compare the European and American protocols directly, as the results would help determine which combination is the safest and most effective.


American Heart Association

“Symptoms and Diagnosis of Venous Thromboembolism (VTE)”
(Updated: October 14, 2016)

The Journal of Sexual Medicine

Arnold, Justin D., MMSc, et al.
“Incidence of Venous Thromboembolism in Transgender Women Receiving Oral Estradiol”
(Full-text. Published online: September 23, 2016)