The thyroid hormones, tri-iodothyronine and thyroxine are transported in the bloodstream bound to proteins; measurement of protein-bound iodine, as opposed to total plasma iodine, was used as an index of thyroid gland activity before more specific methods of measuring the hormones were developed.
The binding of almost all thyroxine in the blood to protein. The measure of the amount is useful as an indicator of the quantity of circulating (in the blood) iodine.
A compound of thyroxine and iodine.
Iodine chemically bound to protein in the serum; measured as a test of thyroid function.