Alkor Bio, Ltd.

Thyroxin (T4) is one of the thyroid gland hormones with a molecular weight of 777 Da. Quantitative determination of serum free thyroxin is significant for evaluation of thyroid gland function. The bulk of serum T4 persists in protein-bound form. The main T4-binding proteins are thyroxin-binding globulin (TBG), thyroxin-binding pre-albumin and albumin. Concentration of non-bound form of T4 (freeT4) is very low, approximately 0,03% of the total concentration of circulating hormone. Namely 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, renal insuffi ciency) and when the binding capacity of the proteins is diminished due to salicylates treatment. So, 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 thyroxin preparations; it is below normal in the case of thyroid hypofunction. ThyroidEIA-free T4 kit is intended for the quantitative determination of free thyroxin in human serum.