WASHINGTON – Novel studies published in the Men’s Health Issue of AACC’s journal Clinical Chemistry suggest that hormone therapy for transgender people increases the risk of blood clots less than birth control pills and does not increase the risk of cardiovascular disease at all. These preliminary results could help more transgender individuals to access essential hormone therapy by increasing physician comfort with prescribing it.

All major medical associations agree that transgender individuals need to be able to express their gender in ways with which they feel comfortable and that this is the most effective treatment for psychological distress caused by incongruence between sex assigned at birth and gender. For many transgender individuals, expressing their gender involves physically changing their body through medical steps such as taking hormone therapy. However, transgender patients often experience difficulty getting hormone therapy prescriptions, to the point that 1 in 4 transgender women have to resort to illegally obtaining cross-sex hormones. Part of this is because existing research on transgender hormone therapy is limited and conflicting, which has led to some physicians denying patients this treatment out of concern that it could significantly increase the risk of health problems such as blood clots and cardiovascular disease.

A team of researchers led by Dina N. Greene, PhD, of the University of Washington in Seattle has now estimated that in transgender women prescribed estrogen, blood clots only occur at a rate of 2.3 per 1,000 person-years. While this is higher than the estimated incidence rate of blood clots in the general population (1.0-1.8 per 1,000 person-years), it is less than the estimated rate in premenopausal women taking oral contraceptives (3.5 per 1,000 person-years), which means that it is an acceptable level of risk. In order to determine this, Greene’s team performed a systematic review of all studies that have included the incidence rate of blood clots in transgender women receiving estrogen therapy, identifying 12 that were most relevant. The researchers then used meta-analysis to combine the results of these 12 studies and calculate a risk estimate that is based on all available evidence to date.

“Documenting the risks associated with hormone treatment may allow for prescribers to feel more comfortable with prescribing practices, allowing for better overall management of transgender people,” said Greene. “Our data support the risk of thrombotic events in transgender women taking estrogen therapy being roughly comparable to the risk of thrombotic risks associated with oral contraceptives in premenopausal women. Given the widespread use of oral contraception, this level of risk appears to be broadly accepted.”

In a second study, a team of researchers led by Guy G.R. T’Sjoen, MD, PhD, also conducted a systematic review of all studies that have measured risk factors for cardiovascular disease in transgender people taking hormone therapy. The researchers identified 77 relevant studies in this area and found that the majority of them report no increase in cardiovascular disease in either transgender men or women after 10 years of hormone therapy. The studies that did indicate a higher cardiovascular disease risk for transgender women in particular mainly involved patients using ethinyl estradiol, a now obsolete estrogen agent, and are therefore no longer valid.

T’Sjoen’s team does state that their results are not conclusive due to the small sample sizes and relatively short duration of the studies in this area (and Greene’s team included a similar caveat for their work). However, it is important to look at Greene and T’Sjoen’s studies in the context of transgender research as a whole. The field only began to receive National Institutes of Health funding in 2017 and is also lagging due to the fact that transgender patients often aren’t identified in medical databases that provide data for research. In light of this, these studies are significant not only because they suggest that transgender hormone therapy is safe, but also because they underscore the need for longer-term, large scale studies involving this underserved population.

About AACC

Dedicated to achieving better health through laboratory medicine, AACC brings together more than 50,000 clinical laboratory professionals, physicians, research scientists, and business leaders from around the world focused on clinical chemistry, molecular diagnostics, mass spectrometry, translational medicine, lab management, and other areas of progressing laboratory science. Since 1948, AACC has worked to advance the common interests of the field, providing programs that advance scientific collaboration, knowledge, expertise, and innovation. For more information, visit www.aacc.org.

Clinical Chemistry is the leading international journal of clinical laboratory science, providing 2,000 pages per year of peer-reviewed papers that advance the science of the field. With an impact factor of 8.636, Clinical Chemistry covers everything from molecular diagnostics to laboratory management.