Radioimmunoassay

Radioimmunoassay is a general method for the determination of the concentration of virtually any substance by comparison of its inhibitory effect on the binding of radioactively labeled antigen to specific antibody with the inhibitory effect of known standards. Requirements for the assay include labeled antigen, specific antibody, standard antigen immunochemically identical to the unlabeled antigen in unknown samples, and a method for the separation of antibody-bound from free labeled antigen, since the antigen-antibody complexes generally do not precipitate spontaneously. Problems encountered in radioimmunoassay include nonhormonal factors which interfere in the chemical reaction and cross-reacting prohormones, molecular fragments, and related hormonal antigens which may alter the specificity of the immune reaction.