Are there reasons for a rise in TSH levels other than being given estrogen while on levothyroxine?
” — JG, Foster City, CA Estrogens increase thyroxine-binding globulin, a protein which binds over 99% of the thyroid hormone present in the blood. Thyroid hormone bound to TBG represents a circulating storage pool of thyroid hormone and is not readily available to other organs such as liver and kidney. The thyroid hormone that is unbound or “free” is readily available to other tissues. In normal individuals, the increase in TBG results in a transient increased production of thyroid hormone to saturate the extra TBG in the blood and maintain the normal level of unbound thyroid hormone. In patients who are being treated with thyroid tablets because their own thyroid is unable to produce a normal amount of thyroid hormone, it is possible that a higher dose of thyroid hormone might be necessary after beginning estrogen therapy. It is uncertain how commonly this occurs. Women taking thyroid hormone for hypothyroidism who become pregnant may require as much as 45% more thyroxine – however o
