Free Т4 ELISA kit

The Free T4 ELISA kit is intended for quantitative determination of free thyroxine in human serum.

Thyroxine (T4) is one of the thyroid gland hormones with molecular mass of 777 Da. Determination of free thyroxine in serum is significant for evaluation of thyroid gland function.

The bulk of serum T4 persists in protein-bound form. Main T4-binding proteins are thyroxine-binding globulin (TBG), thyroxine-binding prealbumin and albumin. Concentration of free non-bound form of T4 (freeT4) is very low, approximately 0.03% of total concentration of circulating hormone. Free T4 is considered to be responsible for biological activity of the hormone. Free T4 concentration does not depend on the concentration of binding proteins and remains normal when TBG levels are either increased (e.g. due to congenital pathology, pregnancy, intake of estrogens and oral contraceptives) or decreased (e.g. due to congenital pathology, administration of androgens and salicylates, or renal insufficiency) and if the binding capacity of proteins is diminished after treatment by salicylates. Thus, free T4 level adequately reflects the actual thyroid status. Concentration of free T4 is above normal in patients with thyroid hyperfunction or after intake of thyroxine preparations; it is below normal level in case of  thyroid hypofunction.