Thyroxin Hormone (fT4) ELISA
A solid-phase enzyme immunoassay for the quantitative determination of free thyroxin in blood serum or plasma.
Thyroid hormones thyroxin (T4) and 3,5,3’-triiodothyronine (T3) exert regulatory influences on growth, differentiation, cellular metabolism and development of skeletal and organ systems. T4 and T3 in blood are found both in free and bound form – mostly, they are bound to thyroxin binding globulin (TBG). Only free forms of T3 and T4 exert hormonal activity also their percentage is very low – 0.3% for T3 and 0.03% for T4.
The concentration of T4 is generally accepted as an index of thyroid function which provides enough information to differentiate between hyper-, hypo- and euthyroidism.
Elevation of total T4 is found in hyperthyroidism, in patients with tumors of pituitary gland, in subjects with elevated TBG level (pregnancy, acute or chronic active hepatitis, estrogen-secreting tumors or estrogen intake, hereditary elevation of TBG), in patients taking oral contraceptives, heroin, methadone, thyroid preparations, TSH, thyroliberin.
Low total T4 is found in hypothyroidism, in patients with panhypopituitarism, in subjects with low TBG level (acromegaly, nephritic syndrome, hypoproteinemia, chronic liver diseases, androgen-secreting tumours, hereditary reduction), in patients taking aminosalicylic and acetylsalicylic acids, cholestyramine, reserpine, potassium iodide, triiodothyronine.
This test is based on competition enzyme immunoassay principle. Tested specimen is placed into the microwells coated by specific murine monoclonal to T4-antibodies simultaneously with conjugated fT4-peroxidase. fT4 from the specimen competes with the conjugated fT4 for coating antibodies. After washing procedure, the remaining enzymatic activity bound to the microwell surface is detected and quantified by addition of chromogen-substrate mixture, stop solution and photometry at 450 nm. Optical density in the microwell is inversely related to the quantity of the measured analyte in the specimen.
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