Laboratory Changes During Gender-Affirming Hormone Therapy in Transgender Adolescents

OBJECTIVES Guidelines for monitoring of medications frequently used in the gender-affirming care of transgender and gender-diverse (TGD) adolescents are based on studies in adults or other medical conditions. In this study, we aimed to investigate commonly screened laboratory measurements in TGD adolescents receiving gender-affirming hormone therapy (GAHT). METHODS TGD adolescents were recruited from 4 study sites in the United States before beginning GAHT. Hemoglobin, hematocrit, hemoglobin A1c, alanine transaminase, aspartate aminotransferase, prolactin, and potassium were abstracted from the medical record at baseline and at 6, 12, and 24 months after starting GAHT. RESULTS Two-hundred and ninety-three participants (68% designated female at birth) with no previous history of gonadotropin-releasing hormone analog use were included in the analysis. Hemoglobin and hematocrit decreased in adolescents prescribed estradiol (-1.4 mg/dL and -3.6%, respectively) and increased in adolescents prescribed testosterone (+1.0 mg/dL and +3.9%) by 6 months after GAHT initiation. Thirteen (6.5%) participants prescribed testosterone had hematocrit > 50% during GAHT. There were no differences in hemoglobin A1c, alanine transaminase, or aspartate aminotransferase. There was a small increase in prolactin after 6 months of estradiol therapy in transfeminine adolescents. Hyperkalemia in transfeminine adolescents taking spironolactone was infrequent and transient if present. CONCLUSIONS Abnormal laboratory results are rare in TGD adolescents prescribed GAHT and, if present, occur within 6 months of GAHT initiation. Future guidelines may not require routine screening of these laboratory parameters beyond 6 months of GAHT in otherwise healthy TGD adolescents.