Radioimmunoassay (RIA)

Radioimmunoassay (RIA) is a sensitive method for measuring very small amounts of a substance in the blood. Radioactive versions of a substance, or isotopes of the substance, are mixed with antibodies and inserted in a sample of the patient's blood. The same non-radioactive substance in the blood takes the place of the isotope in the antibodies, thus leaving the radioactive substance free.

The amount of free isotope is then measured to see how much of the original substance was in the blood. This isotopic measuring method was developed in 1959 by two Americans, biophysicist Rosalyn Yalow (1921-) and physician Solomon A. Berson (1918-1972).

History

Yalow and Berson developed the first radioisotopic technique to study blood volume and iodine metabolism. They later adapted the method to study how the body uses hormones, particularly insulin, which regulates sugar levels in the blood. The researchers proved that Type II (adult onset) diabetes is caused by the inefficient use of insulin. Previously, it was thought that diabetes was caused only by a lack of insulin.

In 1959 Yalow and Berson perfected their measurement technique and named it radioimmunoassay (RIA). RIA is extremely sensitive. It can measure one trillionth of a gram of material per milliliter of blood. Because of the small sample required for measurement, RIA quickly became a standard laboratory tool.

How RIA Works

As an example of how this technique works, let's apply it to insulin. To measure insulin, the first step is to mix known amounts of radioisotope-tagged insulin and antibodies. These combine chemically. Next, a small amount of the patient's blood is added. The insulin contained in the blood displaces some of the tagged insulin. The free-tagged insulin is then measured with isotope detectors and the patient's insulin level is calculated.

Uses for RIA

RIA has many uses, including narcotics (drug) detection, blood bank screening for the hepatitis (a highly contagious condition) virus, early cancer detection, measurement of growth hormone levels, tracking of the leukemia virus, diagnosis and treatment of peptic ulcers, and research with brain chemicals called neurotransmitters.

radioimmunoassay A technique for the very precise analysis of proteins such as polypeptide hormones, antigens, antibodies, and enzymes. It is based on the ability of unlabelled proteins to inhibit competitively the binding of labelled protein by specific antibodies (i.e. an immunological reaction). A radioactive label (e.g. radioactive iodine) may be used to follow the interaction of an antibody with an antigen. The amount of radioactivity in the antibody–antigen precipitate is a measure of the degree of inhibition. The protein concentration of the unknown sample is determined by comparing the degree of inhibition with that produced by a series of standards containing known amounts of the protein. The technique has been adapted to assay nonproteins, such as steroids and nucleotides.

radioimmunoassay A technique for the very precise analysis of proteins, based on the ability of unlabelled proteins to inhibit competitively the binding of labelled protein by specific antibodies (i.e. an immunological reaction). The protein concentration of the unknown sample is determined by comparing the degree of inhibition with that produced by a series of standards containing known amounts of the protein. The technique has been adapted to assay nonproteins.

radioimmunoassay (RIA) A sensitive quantitative method for detecting trace amounts of a biomolecule, based on its capacity to displace a radioactively labelled form of the molecule from combination with its antibody. See also immunoassay.

radioimmunoassay (ray-di-oh-im-yoo-noh-ass-ay) n. the technique of using radioactive antibodies as tracers to estimate the levels of natural substances, especially hormones, in the blood, which act as antigens. The amount of radioactivity trapped is a measure of the amount of the antigen present.