Radioimmunoassay (RIA)

Abstract

Radioimmunoassay (RIA), a 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 or pathogen in the body that causes antibody production by the B lymphocytes of the body) 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 Serum containing the antibodies is withdrawn and treated with a radioactive antigen and later with a nonradioactive antigen.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 Yalow. Yalow was awarded the 1977 Nobel Prize in Physiology or Medicine for her work. Radioimmunoassay is an in vitro assay. It calculates the presence of an antigen with very high sensitivity. Mainly, any biological product or substance for which a specific antibody exists can be measured, even in minute concentrations. Radioimmunoassay has been the first immune-assay procedure developed to analyse picomolar and nanomolar concentrations of hormones in biological fluids. The radioimmunoassay is perhaps the oldest types of immunoassays. Here, a radioisotope is attached to an antigen of interest and bound with its complementary antibody. Then a sample with the antigen to be measured is added. It competes with the radioactive antigen, kicks it out of the binding spot and replaces it. After washing away unbound antigens the radioactivity of the sample is measured. The amount of radioactive signal is inversely related to the amount of target antigen.