Radioimmunoassay

A radioimmunoassay is a technique used to detect levels of different substances, usually antigens or hormones in the blood, by using antibodies and forming an antibody-antigen/hormone complex. For example. a radioimmunoassay could measure insulin levels of a particular patient. An antibody-insulin complex would be created (they will bind to each other), but the insulin used will be radioactive labeled insulin. A bunch of these antibody-insulin complexes would be created on a slide, and then the sample of the patients serum will be added in with the slide. If insulin is present in the serum, it will replace some of the radioactively labeled insulin in the previously formed antibody-insulin complexes on the slide. If it is high, it will replace more of them, so there will be more antibodies attached to non-radioactive insulin, and more free radioactive insulin that has been displaced. The antigen-insulin complexes will be precipitated out by the use of a second antibody that attaches to the complex. Then, the radioactivity of the supernatant, which contains all of the free insulin, will be measured. The level of radioactivity quantifies the amount of radioactive insulin that was displaced, which quantifies the level of insulin in the patient.