Correlation of the Red Blood Cell Uptake of I131-L-Triiodothyronine and Thyroxine-Binding Globulin Capacity in Man

Abstract

The thyroxine-binding globulin capacity and the binding coefficient of the red blood cell uptake of I¹³¹-L-triiodothyronine were measured in healthy subjects and in patients with hyperthyroidism and hypothyroidism. The mean thyroxine-binding globulin capacity (17.1 ±5.0 μg/100 ml) is significantly less in hyperthyroid patients than in healthy subjects (20.7 ±4.8 μg/100 ml). The mean thyroxine-binding globulin capacity is elevated in hypothyroid patients (24.3 ±4.6 μg/100 ml). The mean binding coefficients of the red blood cell uptake of I¹³¹-L-triiodothyronine are the same as those previously reported. A significant negative correlation between thyroxine-binding globulin and log of the binding coefficient was found in healthy subjects and in patients with hyperthyroidism and hypothyroidism. The study suggests the physiologic importance of the thyroxine-binding globulin capacity in the cellular uptake of triiodothyronine.