Radioimmunoassay is the in vitro measurement of human hormones, proteins and other trace substances using isotope labeling and the immunological principle of antigen-antibody binding. Radioimmunoassay (RIA) uses radionuclides as tracers. Antigens are labeled with isotopes, and the labeled antigens undergo a reversible immunoconjugation reaction with antibodies and compete with unlabeled standards. Measurement of the mass of each substance allows for the calculation of isotope-labeled bound and free antigens, and allows for the calculation of the radioactivity binding rate. Different concentrations of standards are combined with antibodies under the same conditions to obtain the radioactivity binding rates of different concentrations of standards, and a standard curve is plotted. The sample to be tested is put into the same conditions for reaction, and the binding rate of the sample to be tested is compared with the curve to obtain the content of the sample to be tested. Radioimmunoassay can be used for quantitative detection of various hormones, tumor markers, tumor molecular typing, etc. It has been widely used in clinical examination and experimental research.