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Immunoassay for the in vitro quantitative determination of thyroxine in human serum.
The hormone thyroxine (T4) is the main product secreted by the thyroid gland and is an integral component of the hypothalamusanterior pituitary-thyroid regulating system. It has the function of anabolically influencing metabolism. Thyroxine is formed in a coupling reaction from two DIT molecules (3,5-diiodotyrosine) in the thyroid gland. It is stored bound to thyroglobulin in the lumina of the thyroid follicles and is secreted as required under the influence of TSH. (1, 2)
The major part (> 99 %) of total thyroxine (T4) in serum is present in protein-bound form. As the concentrations of the transport proteins in serum are subject to exogenous and endogenous effects, the status of the binding proteins must also be taken into account in the assessment of the thyroid hormone concentration in serum. If this is ignored, changes in the binding proteins (e.g. due to estrogen-containing preparations, during pregnancy or in the presence of a nephrotic syndrome etc.) can lead to erroneous assessments of the thyroid metabolic state. (3, 4, 5, 6, 7)
The determination of T4 can be utilized for the following indications: the detection of hyperthyroidism, the detection of primary and secondary hypothyroidism, and the monitoring of TSH-suppression therapy. (8)
The T4 ELISA test kit employs a competitive test principle with an antibody specifically directed against T4. Endogenous T4,
released by the action of 8-anilino-1-naphthalene sulfonic acid(ANS).
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