The process of RIA involves several key steps. First, a known quantity of radioactive antigen is mixed with a known quantity of antibody. The sample containing the unknown antigen is then added. The competition between the radioactive and non-radioactive antigens for the antibody binding sites forms the basis for quantification. The amount of radioactive antigen bound to the antibody is inversely proportional to the concentration of the unknown antigen in the sample. The bound and free antigens are separated, and the radioactivity of the bound fraction is measured using a gamma counter.
