A sensitive laboratory technique that uses radioactive isotopes to measure the concentration of proteins such as hormones or antibodies in blood.
(See also immunoassay.)
A technique introduced in 1960 which enables the minute quantities of natural substances in the blood such as HORMONES to be measured. A radioimmunoassay depends upon the ability of an unlabelled hormone to inhibit, by simple competition, the binding of isotopically labelled hormone by speci?c ANTIBODIES. The requirements for a radioimmunoassay include adequate amounts of the hormone; a method for labelling the hormone with a radioactive isotope; the production of satisfactory antibodies; and a technique for separating antibody-bound from free hormone. Radioimmunoassay is more sensitive than the best bioassay for a given hormone, and the most sensitive radioimmunoassays permit the detection of picogram (pg = 10?12g) and femtogram (fg = 10?15g) amounts of material.
n. a technique using radioactive antibodies as *tracers to estimate the levels of natural substances in a blood sample. The antibodies bind to antigens, and the amount of radioactivity trapped is a measure of the amount of the target antigen present. The technique is widely used in the estimation of hormone levels.
A glycoprotein hormone secreted by the PLACENTA in early pregnancy, and stimulating the CORPUS LUTEUM within the ovary (see OVARIES) to secrete OESTROGENS, PROGESTERONE, and relaxin. The hormone is essential for the maintenance of pregnancy up to about 6–8 weeks of gestation. A RADIOIMMUNOASSAY can be used to detect its presence, and pregnancy can be diagnosed as early as six days after conception by testing for it in the urine. Some tumours also secrete human chorionic gonadotrophin, particularly HYDATIDIFORM MOLE, which produces large amounts.... human chorionic gonadotrophin
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