Radioimmunoassay (RIA)- Definition, Principle, Procedure, Results, Uses


Radioimmunoassay (RIA) is a laboratory technique that uses radioisotopes to measure the concentration of a substance in a biological sample. RIA is based on the principle of specific and competitive binding of antigens and antibodies. Antigens are molecules that can elicit an immune response and antibodies are proteins that can recognize and bind to antigens.

In RIA, a known amount of a radiolabeled antigen (an antigen that has been attached to a radioactive atom) is mixed with a known amount of a specific antibody. The antibody binds to the radiolabeled antigen, forming an antigen-antibody complex. Then, a sample containing an unknown amount of the same antigen (unlabeled antigen) is added to the mixture. The unlabeled antigen competes with the radiolabeled antigen for binding to the antibody. The more unlabeled antigen there is in the sample, the less radiolabeled antigen will be bound to the antibody.

The mixture is then separated into two fractions: one containing the bound antigen-antibody complex and one containing the free antigens (both labeled and unlabeled). The radioactivity of each fraction is measured using a device called a gamma counter. The radioactivity of the bound fraction reflects the amount of radiolabeled antigen that is bound to the antibody, while the radioactivity of the free fraction reflects the amount of radiolabeled antigen that is displaced by the unlabeled antigen. By comparing the radioactivity of the two fractions, the concentration of the unlabeled antigen in the sample can be calculated.

RIA is a very sensitive technique that can detect very low levels of substances in biological samples. RIA can be used to measure hormones, drugs, antibodies, viruses, toxins and other molecules of interest. RIA has many applications in biomedical research, clinical diagnosis and environmental monitoring. However, RIA also has some limitations, such as the use of radioactive materials, the high cost of equipment and reagents, and the short shelf-life of radiolabeled substances.