Effects of 12 Months' Treatment with Testosterone Undecanoate on Markers for Erythropoietic Activity and Safety Aspects in Transgender and Cisgender Hypogonadal Men.

Background: To investigate the erythropoietic activity and safety aspects of testosterone undecanoate (TU) injections in transgender men, assigned female at birth.

Methods: Twenty-three men (13 hypogonadal cisgender men and 10 transgender men) who initiated TU at the study start (naïve) and 15 men (10 hypogonadal cisgender men and 5 transgender men) on steady-state treatment with TU (non-naïve) were included in this prospective 1-year observational study. A control group of 32 eugonadal cisgender men was investigated once at baseline. Complete blood count, testosterone in serum and saliva, and plasma lipids, and liver enzymes were assessed.

Results: For naïve transgender men, a significant increase in hemoglobin concentration was noted (mean (SD)), 141 (8) g/L to 151 (13) g/L, while no increase was seen in naïve hypogonadal cisgender men. At the end of the study, naïve transgender men exhibited comparable levels of hemoglobin, hematocrit, and testosterone levels in serum and saliva to hypogonadal cisgender men, as well as to the eugonadal cisgender men. During the study, HDL-cholesterol decreased significantly in naïve transgender men, 1.4 (0.4) mmol/L to 1.2 (0.4) mmol/L, P = 0.03, whereas no significant change was noted in naïve hypogonadal cisgender men. Liver enzymes remained unchanged in all groups.

Conclusions: After 12 months of treatment with TU in naïve transgender men, hemoglobin and hematocrit increased to levels within the cisgender male reference range. A slight decrease in HDL-cholesterol was seen in naïve transgender men but liver enzymes remained unchanged.