A standard concern about gender-affirming hormone therapy for transmasculine people is the danger of red blood cell volume changes and erythrocytosis, a high concentration of red blood cells, with using prescribed testosterone. Nonetheless, Mount Sinai researchers have found that testosterone treatment could also be safer than previously reported, with results published today in The Journal of Clinical Endocrinology and Metabolism.

Mount Sinai researchers from the Division of Endocrinology and Center for Transgender Medicine and Surgery examined the connection between using testosterone as a part of gender-affirming hormone therapy (GAHT) for transmasculine individuals and changes in hematocrit, a test that measures how much of an individual’s blood is made up of red blood cells. The study of a big North American cohort is the biggest on this subject so far.

A significant concern of patients, providers, and fogeys is the security of hormone therapy for transgender and gender-diverse people. The findings from this study represent very necessary reassurance regarding the security of testosterone as masculinizing treatment. Providers should feel more comfortable prescribing testosterone when it’s indicated. Patients and the families of patients should feel reassured regarding a minimum of this one source of hysteria about treatment.”

Joshua Safer, MD, FACP, FACE, Executive Director of the Mount Sinai Center for Transgender Medicine and Surgery, Professor of Medicine on the Icahn School of Medicine at Mount Sinai, and senior creator of the report

The researchers conducted a cross-sectional evaluation of serum-based testosterone and hematocrit levels in 6,670 transmasculine patients who were prescribed testosterone for GAHT through Plume, a virtual provider of gender-affirming care across 45 states. Patients were included in the event that they had an energetic prescription from Plume for a testosterone product as a part of their GAHT regimen, and up to date hematocrit and testosterone laboratory values available for evaluation. The entire testosterone was measured using liquid chromatography-mass spectrometry, and hematocrit was calculated as a part of a whole blood count. The hematocrit and testosterone laboratory values were collected as a part of the identical blood sample, typically mid-week after a weekly injection, for all patients using injectable types of testosterone.

Researchers found that higher testosterone levels were related to higher hematocrit levels, nevertheless, the magnitude of change in hematocrit was small and unlikely to be clinically meaningful. Only 8.4 percent of transmasculine individuals within the study had a hematocrit greater than 50 percent, and lower than 1 percent had a hematocrit greater than 54 percent, the extent at which treatment for erythrocytosis is advisable, often through using phlebotomy (bloodletting). These numbers are lower than those previously reported in smaller studies, and the finding of such a small degree of change in hematocrit and a lower risk of erythrocytosis should provide more assurance to those prescribing and using testosterone as GAHT.

“Our study found that the numbers of patients on testosterone therapy with abnormal red blood cell elevations were lower than previously reported in smaller studies. It’s noteworthy that in the biggest North American cohort reported so far, lower than 1 percent of transmasculine individuals had a hematocrit level where medical interventions is likely to be required. These results should help providers feel more comfortable prescribing testosterone as a part of GAHT,” said the primary and corresponding creator, Nithya Krishnamurthy, a second-year medical student at Icahn Mount Sinai. “This work suggests a necessity to evaluate the influence of other aspects that may result in secondary erythrocytosis; resembling being obese, smoking tobacco, or using alcohol.”