Triiodothyronine (fT3) ELISA
A solid-phase enzyme immunoassay for the quantitative determination of free triiodothyronine in blood serum or plasma.
Thyroid hormones thyroxin (FT3) and 3,5,3’-triiodothyronine (T3) exert regulatory influences on growth, differentiation, cellular metabolism and development of skeletal and organ systems. FT3 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 FT3 exert hormonal activity also their percentage is very low – 0.3% for T3 and 0.03% for FT3.
The concentration of T3 is much less than that of FT3 but its metabolic activity is about 3 times greater. About 80% of T3 is produced in peripheral tissues by deiodination of FT3, and only 20% is secreted by thyroid gland. That is why in hypothyroid patients T3 level may for a long time remain on the lower limit of the normal range, because its loss may be compensated by enhanced conversion of FT3 into T3. Determination of T3 level is most useful in T3-hyperthyroidism because 5-10% of such patients do not show significant changes in FT3 level while the concentration of T3 is highly elevated.
Elevated T3 levels are seen in early thyroid hypofunction, after intake of estrogens, oral contraceptives, heroin, methadone, during pregnancy.
Decreased concentrations of T3 are found in an initial stage of hyperthyroidism, acute and subacute thyroiditis, after intake of androgens, dexamethasone, salycilates. Decreased concentrations of T3 are found in the initial stage of hyperthyroidism, acute and subacute thyroiditis, after intake of androgens, dexamethasone, salycilates
This test is based on competition enzyme immunoassay principle. Tested specimen is placed into the microwells coated by specific rabbit polyclonal to T3-antibodies simultaneously with conjugated fT3-peroxidase. fT3 from the specimen competes with the conjugated fT3 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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