Endocrine Abstracts

Background and Objective: It is known that androgens decrease and estrogens increase TBG. In female to male transsexuals under testosterone replacement, decrease of TBG has been shown, but also an increased T3/T4 ratio despite stable free T4 and TSH, suggesting increased conversion to T3 by testosterone. We wanted to study the HPT axis in hypogonadal cis-males before and after testosterone replacement.

Method: Prospective observational study in adult male patients with hypogonadism in the setting of an outpatient endocrine clinic. Serum samples were taken prior to (visit 1) and at the first consultation (visit 2) under testosterone replacement. Males with history of thyroid disorder, having abnormal thyroid function at visit 1, treated with betaHCG, or taking drugs at baseline or during follow-up knowing to affect thyroid function were excluded. Paired t-test or Wilcoxon matched-pairs signed rank test was applied where appropriate.

Results: A cohort of n = 24 hypogonadal male patients was studied. Mean age was 52.9+/- 15.4 years, n = 17 patients were treated for structural hypogonadism (n = 8 hypogonadotropic, n = 9 hypergonadotropic), n = 7 patients were treated for functional hypogonadism. Median time between visit 1 and 2 was 2.53 months [range 1.15-11.5]. As expected, total and free testosterone increased significantly (see Table). TSH was not different, but T4 (total and free) decreased. Total T3 was not different, and T3/T4 ratio increased between visit 1 and 2.

Conclusion: In euthyroid hypogonadal cis-males, testosterone replacement did not alter TSH, decreased total T4 and free T4, but not total T3. The increased T3/T4 ratio suggests increased conversion and/or or differential binding to TBG.