Radioimmunoassay is a scientific method used to test hormone levels in the blood without the need to use a bioassay. It involves mixing a radioactive antigen (frequently labelled with isotopes of iodine attached to tyrosine) with antibody to that antigen, then adding unlabeled or "cold" antigen in known quantities and measuring the amount of labeled antigen displaced. A hormone (from Greek horman - to set in motion) is a chemical messenger from one cell (or group of cells) to another. ... Red blood cells (erythrocytes) are present in the blood and help carry oxygen to the rest of the cells in the body Blood is a circulating tissue composed of fluid plasma and cells (red blood cells, white blood cells, platelets). ... Also known as a biological assay, a bioassay is a measurement of the effects of a substance on living organisms. ... Radioactivity may mean: Look up radioactivity in Wiktionary, the free dictionary. ... An antigen is a molecule that stimulates the production of antibodies. ... Isotopes are forms of an element whose nuclei have the same atomic number–-the number of protons in the nucleus--but different atomic masses because they contain different numbers of neutrons. ... General Name, Symbol, Number iodine, I, 53 Chemical series halogens Group, Period, Block 17, 5, p Appearance violet-dark gray, lustrous Atomic mass 126. ... Tyrosine (from the Greek tyros, meaning cheese, as it was first discovered in cheese), 4-hydroxyphenylalanine, or 2-amino-3(4-hydroxyphenyl)-propanoic acid, is one of the 20 amino acids that are used by cells to synthesize proteins. ... Wikipedia does not yet have an article with this exact name. ...

Initially, the radioactive antigen is bound to the antibodies. When cold antigen is added, the two compete for antibody binding sites - and at higher concentrations of cold antigen, more binds to the antibody, displacing the radioactive variant. The bound antigens are separated from the unbound ones in solution and the radioactivity of each used to plot a binding curve.

The technique is both extremely sensitive, and specific, if costly, and it is especially useful in diagnosing and treating autoimmune diseases such as Hashimoto's thyroiditis and Systemic Lupus Erythematosus. The sensitivity of a binary classification test or algorithm, such as a blood test to determine if a person has a certain disease, or an automated system to detect faulty products in a factory, is a parameter that expresses something about the tests performance. ... In binary testing, e. ... Autoimmune diseases arise from an overactive immune response of the body against substances and tissues normally present in the body. ... Hashimotos thyroiditis is the most common form of thyroiditis, an autoimmune disease where the bodys own antibodies fight the cells of the thyroid. ...