Resin Uptake of I¹³¹-Labeled Tri-Iodothyronine as a Test of Thyroid Function

THE thyroid hormones, thyroxine and tri-iodothyronine (T3), circulate in plasma bound in dissociable linkage to specific proteins. The hormone-binding proteins defined to date consist of thyroxine-binding globulin (TBG), thyroxine-binding prealbumin (TBPA) and albumin.1 2 3 4 5 Collectively these may be referred to as thyroid-hormone-binding protein (TBP). Albright et al.6 demonstrated that TBP in the serum of hypothyroid subjects is less saturated, and that of hyperthyroid subjects more saturated, than the serum of euthyroid subjects. Hamolsky and his co-workers7 introduced a method for evaluating the saturation of the TBP by studying the incorporation in vitro by the human erythrocyte of I131-labeled . . .