The principle of RIA involves the competition between a radioactively labeled antigen (tracer) and the unlabeled antigen for a fixed number of antibody binding sites. The procedure typically follows these steps:
Mixing the sample containing the unknown amount of antigen with a known quantity of radioactive antigen and specific antibodies. Allowing the antigen-antibody reaction to reach equilibrium. Separating the bound antigen-antibody complexes from the free antigens. Measuring the radioactivity of the bound fraction to determine the amount of antigen in the sample.
