Endocrine Abstracts

Thyroid hormone is considered the easiest hormone to replace as it can be taken orally, has a long half-life allowing once daily dosing, and serum levels can be monitored accurately using thyroid function tests. However, in repeated surveys up to 50% of patients on thyroxine do not have thyroid hormone levels in the reference range and the potential long-term consequences in terms of cardiovascular and bone health have recently been re-evaluated in large cohorts. Community surveys have also repeatedly shown decreased psychological well-being in people on thyroxine, although the basis of this remains controversial. Recent studies have highlighted that variation in the activity of cell membrane transporters and deioidinases between tissues means that serum levels of thyroid hormone do not necessarily reflect active levels of thyroid hormone within tissues. Current research is using genetic variation to determine the effect of differences in deiodinase activity between individuals on requirements for thyroid hormone. This may also prompt a re-evaluation of the role of combined T4 and T3 replacement in selected individuals.