Radioimmunology

Radioimmunology is a laboratory technique that uses the principles of radioimmunoassay (RIA) and immunoradiometric assay (IRMA) to measure the concentration of antigens or antibodies in a biological sample. These assays rely on the specific binding of an antibody to its corresponding antigen. In a typical RIA, a known amount of radiolabeled antigen is mixed with a sample containing an unknown amount of the same antigen and a limited amount of antibody. The unlabeled antigen in the sample competes with the radiolabeled antigen for binding to the antibody. After incubation, the antibody-bound antigen is separated from the free antigen, and the radioactivity of either the bound or free fraction is measured. The amount of radioactivity is inversely proportional to the concentration of the unlabeled antigen in the sample.

IRMA, on the other hand, uses an excess of antibody. In this assay, a known amount of antibody, often immobilized on a solid phase like a microplate well, is mixed with the sample. A second antibody, labeled with a radioisotope and specific for a different epitope on the same antigen, is then added. The amount of radioactivity bound is directly proportional to the concentration of the antigen in the sample. Radioimmunology has been widely used in clinical diagnostics for measuring hormones, drugs, and disease markers. However, due to the use of radioactive materials, concerns about safety and disposal, and the development of non-isotopic immunoassay technologies, its use has declined in favor of methods like ELISA and chemiluminescence assays.