Choice of Hormone Assay to Monitor Feminizing Gender-Affirming Hormone Therapy.

Changes in testosterone concentrations were inversely correlated with changes in estradiol concentrations in transfeminine individuals on feminizing GAHT.

• Cross-sectional analysis of 9916 transfeminine individuals prescribed estradiol.
• The inverse correlation between T and E2 concentrations was statistically significant (P < .001).
• This was the most recent serum T and E2 concentrations analyzed per individual.

Orchiectomy, age, and use of spironolactone were associated with changes in testosterone concentrations but not estradiol concentrations.

• All three factors (orchiectomy, age, spironolactone use) reached statistical significance for association with T concentrations (P < .001).
• None of these factors were significantly associated with changes in E2 concentrations.
• This dissociation suggests T and E2 are not interchangeable monitoring parameters.

Changes in testosterone concentrations were correlated with changes in luteinizing hormone (LH) concentrations.

• The correlation between T and LH concentrations was statistically significant (P < .05).
• This correlation was not demonstrated between E2 and LH concentrations.
• This finding supports LH as a potential monitoring tool, particularly in post-orchiectomy patients.

FSH correlations were examined but did not show the same pattern of association with T or E2 as LH.

• Follicle stimulating hormone (FSH) was included as one of the four assays evaluated for monitoring feminizing GAHT.
• The abstract does not report significant correlations between FSH and T or E2 concentrations comparable to those found for LH.
• The study examined serum T, serum E2, LH, and FSH concentrations in the context of feminizing GAHT treatment.

The authors recommend favoring testosterone concentration targets over estradiol concentration targets for monitoring feminizing GAHT in patients with testes, and considering LH in post-orchiectomy patients not on GnRH agonists.

• Recommendation is based on T being influenced by clinically relevant factors (orchiectomy, age, spironolactone) that E2 is not.
• LH is suggested as a monitoring tool for individuals without testes, with the caveat that GnRH agonist use would suppress LH independently.
• The study population consisted of 9916 transfeminine individuals, representing a large real-world sample.