Serum protein-bound iodine or total thyroxine.

on thyroxine-binding proteins (UTBP), T4 bound to thyroxine-binding proteins (PBI or TBPT4) andfree thyroxine (FT4). thyroid status. This is shown in diagrammatic fashion in fig 1 which illustrates the changes that occur in thyrotoxicosis and hypothyroidism and in those situations where there are alterations in thyroxine-binding protein capacity, such as the increase in thyroxine-binding globulin (TBG) that accompanies pregnancy. The PBI and T4 and their variants define merely one aspect of thyroid hormone secretion and there are other tests available which may be better for evaluating thyroid status, for example, free thyroxine in serum (FT4) (Ingbar, Braverman, Dawber, and Lee, 1965; Sterling and Brenner, 1966), total and free serum triiodothyronine (Sterling, Bellabarba, Newman, and Brenner, 1969; Chopra, Solomon, and Beall, 1971; Mitsuma, Nikei, Gershengorn, and Hollander, 1971; Jacobs, Mackie, Eastman, Ellis, Ekins, and McHardy-Young, 1973), and urinary thyroxine and triiodothyronine (Chan and Landon, 1972; Chan, Besser, Landon, and Ekins, 1972; Burke, Shakespear, and Fraser, 1972) (table I).