Effects of gender affirming hormone treatment in transgender individuals - a retrospective cohort study.

Purpose: Gender affirming hormone treatment (GAHT) results in measurable changes to anthropomorphic, biochemical and hormonal variables that are important to patients and their health care professionals to guide treatment. This study sought to quantify changes which occur in response to initiation of GAHT.

Methods: We performed a retrospective cohort study of outcomes in transgender and gender diverse (TGD) patients starting GAHT. The primary outcome was proportion of patients and time required to achieve optimal hormone levels after commencement of GAHT. Additional analyses were performed to assess whether clinical and biochemical factors were associated with likelihood of achieving target hormone levels.

Results: 345 patients were included. Among 154 transmasculine individuals, 116 (75%) achieved a testosterone level >10 nmol/L during follow-up at a median of 4-months (IQR 4-9). No clinical or biochemical factors were significantly associated with likelihood of reaching therapeutic testosterone concentrations in transmen. Among 191 transfeminine individuals, 131 (72%) achieved a testosterone level <2.0 nmol/L during follow-up at a median of 4-months (IQR 3-9). Factors associated with increased likelihood of testosterone suppression were use of subdermal estradiol implants as well as cyproterone acetate as an androgen antagonist. Changes in differing directions were observed during repeated measures of lipids, liver function, and blood count between transmasculine and transfeminine individuals, reflecting the important effects of testosterone and estradiol on biochemical tests ordered as part of routine clinical care.

Conclusion: Most TGD patients achieve target testosterone levels within 9 months of GAHT initiation. Adverse effects of GAHT are rare, and are usually mild.