Radioimmunoassay (RIA) is a laboratory method that measures, with relative accuracy, minute amounts of substances present in the body. When it was developed in the 1950’s, radioimmunoassay was considered a revolution in medical investigations. As of 2009, it is still considered revolutionary because it is the blueprint for more advanced methods of laboratory techniques.

First discovered by Rosalyn Yalow and Solomon Berson, radioimmunoassay was used to investigate blood volume, iodine metabolism, and hormones like insulin. Radioimmunoassay has expanded its viability by being able to measure trace amounts of substances using sensitive laboratory techniques. Drugs, antigens and hormones are some of the substances measured by radioimmunoassay.

Radioimmunoassay is a specific scientific process. First, laboratory technicians must obtain a substance that contains the antigen they are testing for. This antigen is then injected with radioactive chemicals, such as a gamma-radioactive isotope made from iodine or some other substance. The radioactive chemicals cause the antigen to become radioactive, so it can be observed.

The radioactive antigen is then mixed with a set amount of antibodies that scientists have determined are appropriate. The antigens and antibodies bind to each other and become one substance. This provides the benchmark or basis for testing. Then, an unknown substance which contains some tiny amount of the antigen is added. This new substance is the substance being tested.

When the new substance, called the cold or unlabeled substance is added, the antigens in the new substance try to also join with antibodies. As they do, they displace the radioactive substances that were joined to these antibodies. The radioactive substances break away from the antibodies. Scientists can then measure the amount of free radioactive agents that have become unbound to create a binding curve. The binding curve shows the amount of antigens in the unknown substance.

Radioimmunoassay is considered the pioneer in nuclear medicine radioactive measurements because radioactive substances show up with great clarity and accuracy. The uses of radioimmunoassay are varied and include blood-bank screening for hepatitis, drug detection, tracking viruses, early detection of leukemia and other cancers, measurement of human growth hormones, and aid in the detection of many kinds of ulcers like peptic ulcers.

More advanced methods, notably ELISA, which rely less heavily in radioactive substances, have all but replaced radioimmunoassay in most applications. ELISA utilizes a biochemical process and bypasses the need for radioactive elements. These new methods are both less dangerous and less costly for scientists.