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(RIA), highly sensitive laboratory technique used to measure minute amounts of substances including antigens, hormones, and drugs present in the body. The substance or antigen (a foreign substance in the body that causes antibody production) to be measured is injected into an animal, causing it to produce antibodies. Serum containing the antibodies is withdrawn and treated with a radioactive antigen and later with a nonradioactive antigen. Measurements of the amount of radioactivity are then used to determine the amount of antigen present. The technique was developed by Solomon Berson and Rosalyn YalowYalow, Rosalyn Sussman,
1921–2011, American medical physicist, b. New York City, Ph.D. Univ. of Illinois, 1945. As a researcher at the Bronx Veterans Administration Hospital (from 1947), Yalow and colleague Solomon A.
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. Yalow was awarded the 1977 Nobel Prize in Physiology or Medicine for her work.
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A general method employing the reaction of antigen with specific antibody, permitting measurement of the concentration of virtually any substance of biologic interest, often with unparalleled sensitivity. The basis of the method is summarized in the competing reactions shown in the illustration. The unknown concentration of the antigenic substance in a sample is obtained by comparing its inhibitory effect on the binding of radioactively labeled antigen to a limited amount of specific antibody with the inhibitory effect of known standards.

Competing reactions that form basis of radioimmunoassay; * indicates the labeled antigen, and † “in known standard solutions or unknown samplesenlarge picture
Competing reactions that form basis of radioimmunoassay; * indicates the labeled antigen, and † “in known standard solutions or unknown samples

A typical radioimmunoassay is performed by the simultaneous preparation of a series of standard and unknown mixtures in test tubes, each containing identical concentrations of labeled antigen and specific antibody. After an appropriate reaction time the antibody- bound (B) and free (F) fractions of the labeled antigen are separated by one of a variety of techniques. The B/F ratios in the standards are plotted as a function of the concentration of unlabeled antigen (standard curve), and the unknown concentration of antigen is determined by comparing the observed B/F ratio with the standard curve.

The radioimmunoassay principle has found wide application in the measurement of a large and diverse group of substances in a variety of problems of clinical and biological interest. It is therefore not unexpected that there are differences in the specific methods employed for the assay of a particular substance. The full potential of the method has yet to be exploited. It seems that virtually any substance of biologic interest can be measured, the method being modified according to the characteristics of the particular substance. See Antibody, Antigen, Immunology

McGraw-Hill Concise Encyclopedia of Bioscience. © 2002 by The McGraw-Hill Companies, Inc.


A sensitive method for determining the concentration of an antigenic substance in a sample by comparing its inhibitory effect on the binding of a radioactivity-labeled antigen to a limited amount of a specific antibody with the inhibitory effect of known standards.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
The global radioimmunoassay market was valued at USD 345.2m in 2014.
Irwin, "Comparison of radioimmunoassay and chemiluminescent assay methods to estimate canine blood cortisol concentrations," Australian Veterinary Journal, vol.
Direct measurement of progesterone in plasma and milk by a simple solidphase radioimmunoassay. Vet.
The radioimmunoassay analysis of insulin content performed 4 days after the treatment with 100 [micro]g/kg/day of either [E.sub.2] or BPA produced similar results as those presented with immunocytochemistry (Figure 3E).
Using a technique called radioimmunoassay of hair (RIAH), the company can confirm if illegal drugs--marijuana, cocaine, opiates (heroin), methamphetamine, or PCP--have been used during the past three months.
For each specimen, a 3/4-punch (equivalent to a 12-uL blood specimen) was obtained from one blood spot and was tested for benzoylecognine (BE)--a primary cocaine metabolite--using a modified radioimmunoassay (RIA) (2).
By breaking down hair proteins and using radioimmunoassay, Baumgartner claimed he could detect marijuana, cocaine, opiates, amphetamine or PCP in amounts as small as one-billionth of a gram.
Downs used crossover immunoelectrophoresis, Lowenstein radioimmunoassay, and the third group a dipstick clinicians use to detect hemoglobin in urine.
Urinalysis and new techniques such as radioimmunoassay of hair samples are discussed, but given that all these techniques are |new' in the British context, BGC readers might be particularly interested in the discussion of |Ethical Concerns and Legal Issues' (pp.
Determination of blood plasma hormone concentrations using radioimmunoassay. Alterations in hormonal metabolic pathways are detected along with the appearance of unusual or stress-related metabolic compounds.
Section three presents perspectives on palytoxin-one of the most potent coronary vasoconstrictors known-including its pharmacological action, antibody production and development of a radioimmunoassay for it, and other pharmacological and toxicological studies.
Immunodiagnostics are divided into western blot, radioimmunoassay, enzyme-linked immunospot assays, rapid tests and enzyme linked immunosorbent assay.