- A very sensitive, specific laboratory test (assay) using radiolabeled (and unlabeled) substances in an immunological (antibody-antigen) reaction.
* * *An immunologic (immunochemical) procedure that uses the competition between radioisotope-labeled antigen or other substance and unlabeled antigen for antiserums, resulting in quantitation of the unlabeled antigen; any method for detecting or quantitating antigens or antibodies using radiolabeled reactants. Minute quantities of enzymes, hormones, or other substances can be assayed.
* * *ra·dio·im·mu·no·as·say .rād-ē-ō-.im-yə-nō-'as-.ā, -im-.yü-, -a-'sā n immunoassay of a substance (as insulin) that has been radiolabeled abbr. RIAra·dio·im·mu·no·as·say·able -ə-bəl adj
* * *n.a technique using radioactive antibodies as tracer 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.
* * *ra·dio·im·mu·no·as·say (ra″de-o-im″u-no-asґa) a highly sensitive and specific assay method that uses the competition between radiolabeled and unlabeled substances in an antigen-antibody reaction to determine the concentration of the unlabeled substance; it can be used to determine antibody concentrations or to determine the concentration of any substance against which specific antibody can be produced. Abbreviated RIA.
Medical dictionary. 2011.