radioimmunoassay

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radioimmunoassay

 (RIA) [ra″de-o-im″u-no-as´a]
a sensitive assay method that can be used for the measurement of minute quantities of specific antibodies or any antigen, such as a hormone or drug, against which specific antibodies can be raised. An assay for a specific hormone uses antihormone antibody produced by injecting the human hormone into an animal, such as a rabbit, and hormone that has been labeled with a radioisotope. These are mixed with the assay specimen and the antigen (hormone) bound to antibody is separated from the unbound antigen by chromatography or other means. Because any hormone in the assay specimen competes with the radiolabeled hormone for antibody binding sites, the amount of hormone in the specimen is inversely proportional to the radioactivity of the bound fraction or directly proportional to the activity of the free fraction. This is the standard method for clinical laboratory measurements of hormones and is also used for therapeutic drug monitoring, drug abuse screening, and other laboratory tests.

ra·di·o·im·mu·no·as·say (RIA),

(rā'dē-ō-im'yū-nō-as'sā),
An immunologic (immunochemical) procedure that uses competitive inhibition between a radioisotope-labeled antigen or other substance and unlabeled antigen for antiserums, binding as a means to quantify the agent of interest; any method for detecting or quantitating antigens or antibodies using radiolabeled reactants. Minute quantities of enzymes, hormones, or other substances can be assayed.

radioimmunoassay

(rā′dē-ō-ĭm′yə-nō-ăs′ā, -ĭm-yo͞o′-)
n. Abbr. RIA
A technique used to quantitate minute amounts of a substance, such as a hormone, in blood or another liquid. It involves the use of radioisotopes and of antibodies to the substance being investigated.

radioimmunoassay

see RIA.

ra·di·o·im·mu·no·as·say

(RIA) (rā'dē-ō-im'yū-nō-as'sā)
An immunologic (immunochemical) procedure that uses the competition between radioisotope-labeled antigen (hormone) 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.

radioimmunoassay

Any method of measuring the extent of linkage between ANTIGEN and ANTIBODY in which one or other of these is labelled with a radioactive substance (radionuclide). Measurement of radiation can be remarkably precise.