radioimmunoassay (RIA) /rā′dē·ō·im′yənō·as″ā/ [L, radius + immunis, free; Fr, essayer, to try] , a technique in radiology used to determine the concentration of an antigen, antibody, or other protein in the serum. The technique involves the injection of a known amount of a radioactively labeled substance that reacts with the protein in question.
