Estrogen, Thyroxine Binding in Serum, and Thyroxine Therapy

In this issue of the Journal, Arafah presents data indicating that some women with hypothyroidism receiving thyroxine therapy needed more thyroxine when they received estrogen therapy — a change caused by an estrogen-induced increase in the serum concentration of thyroxine-binding globulin.1 The increased need for thyroxine occurred in women with hypothyroidism who were receiving moderate doses of thyroxine, intended to replace normal thyroxine secretion and restore thyrotropin secretion to normal, and in women with thyroid carcinoma who were receiving higher doses of thyroxine, intended to suppress thyrotropin secretion to below normal.Thyroxine-binding globulin is a glycoprotein produced in the liver . . .