Total Thyroxine ELISA (Total T4 ELISA)

The thyroid hormones thyroxine (T4) and triiodothyronine (T3) are synthesized and stored in the thyroid gland and circulate in the bloodstream mostly bound to the plasma protein, thyroxine binding globulin (TBG). 1 The thyroid gland and associated hormones are a major component of the endocrine system. They exert powerful and essential regulatory influences on growth, differentiation, cellular metabolism, and general hormone balance of the body. Proteolytic cleavage of follicular thyroglobulin releases T4 into the bloodstream. Greater than 99% of T4 is reversibly bound to three plasma proteins in blood – thyroxine binding globulin (TBG) binds 70%, thyroxine binding pre-albumin (TBPA) binds 20%, and albumin binds 10%. 2,3 Approximately 0.03% of T4 is in the free, unbound state in the blood at any one time. Diseases affecting thyroid function may present a wide array of confusing symptoms. Measurements of total T4, TSH, Free T3, and Free T4 by immunoassay are reliable and convenient methods to determine the presence of thyroid disorders in patients.4, 5 Increased levels of T4 have been found in hyperthyroidism due to Grave’s disease and Plummer’s disease and in acute and subacute thyroiditis. Low levels of T4 have been associated with congenital hypothyroidism, myxedema, chronic thyroiditis (Hashimoto’s disease), and with some genetic abnormalities. See Product Insert for references.