Immunoradiometric Assay for quantitative determination of thyroid-stimulating hormone (TSH) in human serum or plasma
TSH (Thyroid-stimulating hormone) is a glycoprotein hormone of approximate molecular weight of 28,000 daltons, secreted by the anterior pituitary gland. It consists of two noncovalently bound subunits, known as αand β ‚ the αsubunits are very similar in structure, but the β ‚ subunits differ markedly in amino acid sequence, and are responsible for the differences in the biological specificity of TSH. The main function of TSH is to develop the thyroid gland and also to stimulate and control the secretion of thyroxine (T4) and triiodothyronine (T3). Increase in serum concentrations of TSH is an early and sensitive indicator of decrease thyroid reserve and in conjunction with decreased T4 concentrations is diagnostic of primary hypothyroidism. The secretion and the liberation of TSH are stimulated by the hypothalamic tripeptide TRH (TSH-Releasing Hormone) and are controlled by serum concentrations of the thyroid hormones: T4 and T3 through a negative feedback mechanism: in the thyreotrope cells, T4 is desiodinated in T3 which directly inhibits TSH secretion.
The RIAKEY TSH IRMA Tube II is an one step non-competitive immunoradiometric (IRMA) method (“sandwich”). The method employs two highly specific monoclonal anti-TSH antibodies which recognize two different epitopes of the molecule. One antibody is coated on solid phase (coated tube), the other, specific for the TSH and labeled with Iodine-125, is used as a tracer. Antibody-coated polystyrene tubes serve as solid phase. The tracer antibody and the coated antibody react simultaneously with the TSH antigen present in the standards, control serum and samples. Unbounded material is removed by a washing step. The amount of bound tracer will be directly proportional to the TSH antigen concentration and the remaining radioactivity bound to the tubes is measured in a gamma scintillation counter.