Endocrine Abstracts

Introduction: Testosterone is known to have an effect on hematocrit levels, with polycythemia as an unwanted side effect. An increase in hematocrit levels is also seen in transmen after starting cross-sex hormonal treatment (CHT) with testosterone. The aim of this study is to investigate the effect of cross-sex hormonal treatment with testosterone on hematocrit levels in the context of the safety aspects of this treatment. The prevalence, determinants and outcome of secondary polycythemia were studied in a large cohort of transmen.

Methods: Adult female-to-male transpersons who started cross-sex hormonal treatment with testosterone and were monitored with laboratory control of hematocrit levels at our center were included. Polycythemia was defined as a hematocrit>50%, measured at any moment in treatment. The prevalence of a hematocrit >50% and >54% and thrombogenic complications were studied. Determinants in the development of polycythemia studied were age at start of hormonal treatment, tobacco use, medical history, testosterone levels and type of testosterone admission.

Results: Of the 1218 patients included, 24.8% developed a hematocrit (Ht) >50%, 4.2% had a maximum hematocrit of >54% during the median 60 months of follow-up. The relative risk for smokers to develop a Ht>50% was 1.27 (95% CI 0.90–1.78) and 1.67 (95%CI 0.84–3.34) for a Ht>54%. Compared to testosterone gel, for injection with esters the OR for the development of a Ht>50% is 2.00 (CI 1.30-3.08) and for a Ht>54% 4.46 (CI 1.29–15.4). Compared with testosterone undecanoate, the OR is 2.12 (CI 1.25–3.63) for the development of a Ht>50% and 4.12 (CI 1.01–16.9) for the development of a Ht>54% respectively.

Discussion: Polycythemia is seen as a frequent side effect of testosterone admission in transmen. The number in thrombogenic complications was low. Tobacco use increases the risk of developing high hematocrit levels. Compared to testosterone gel, both injections, testosterone esters and testosterone undecanoate, increased the risk to develop polycythemia.