Hormone treatment for trans women may boost VTE risk

Transgender women who initiate cross-sex hormone therapy are at an increased risk of venous thromboembolism (VTE) and ischemic stroke, researchers reported in the Annals of Internal Medicine.

Researchers studied 2,842 transfeminine individuals who were assigned a male gender at birth but identify more as female. All of them were enrolled in Kaiser Permanente health systems in California and Georgia, and were matched to 10 male and 10 female Kaiser Permanente patients based on age, race, study site and year of index date, which was the first recorded evidence of transgender status.

Some trans individuals may undergo medical treatment to more closely align their physical appearance to their gender identity, the study authors pointed out, but research into the cardiovascular outcomes associated with this treatment is sparse.

Two years after the index date, trans women had higher incidence of VTE compared to cisgender men (4.1 additional events per 1,000 participants) and women (3.4 additional events per 1,000 people). At eight years, those absolute increases jumped to 16.7 and 13.7 per 1,000 people, respectively.

Also, among the trans women who underwent estrogen therapy through Kaiser Permanente, adjusted odds of VTE were 2.7 times higher than reference men and 1.5 times higher than reference women. An increase in stroke rate was also more apparent when the analysis focused only on those with confirmed hormone therapy.

“The present study demonstrated that cross-sex estrogen is a risk factor for VTE and probably ischemic stroke among transfeminine persons,” wrote lead author Darios Getahun, MD, PhD, and colleagues. “We also observed that patterns of VTE and ischemic stroke incidence among transfeminine persons receiving hormone therapy were different from those reported in cisgender women receiving hormone replacement therapy. If confirmed, these results may indicate the need for increasing vigilance in identifying long-term vascular side effects of estrogen therapy in transgender patients.”

Getahun et al. found rates of myocardial infarction were greater among transwomen than cisgender women but similar to the incidence observed in men. They didn’t find evidence of any increased risk for transmasculine participants.

The authors noted the primary limitation of their study is it couldn’t account for hormone therapy that people may have received from other sources. This highlights the challenge of quantifying patients’ complete history of hormone use, they said.

“In the meantime, it is critical to keep in mind that the risk for (acute cardiovascular events) in this population must be weighed against the benefits of treatment,” Getahun and coauthors wrote.