Radioimmunoassay, or RIA, is a blood testing technique used to detect the presence of antigens, like insulin and other hormones. The test dates back to the 1950s, however many new applications for RIA tests have been developed since then. Because it uses radioactive materials, RIA testing requires specialized equipment, as well as knowledgeable and careful handling. While it is a very accurate method of testing, it is also relatively expensive.
Preparing the Sample
A trained lab technician prepares a sample by mixing a fixed, known quantity of an antigen labeled with a radioactive isotope, often one of iodine, and a fixed amount of antibody. The radioactive antigen forms a chemical bond with its corresponding antibody.
After the sample has been prepared, the technician adds blood serum from the patient. The unbound antigen in the blood serum replaces the bound antigen in the sample. Bound and unbound antigens are separated, using one of several techniques. The most common is through charcoal absorption of the antibody and bound antigen.
After separation, the technician measures the amount of radioactivity given off by the replaced bound antigen, which allows the lab to calculate the amount of antigen that was present in the blood serum sample. The more radioactivity produced by the bound antigen, the lower the concentration of the free antigen in the sample. The less radioactive the bound antigen, the higher the concentration of the free antigen in the sample.
RIA can be used to test for the presence of insulin in the bloodstream, a crucial tool in the diagnosis and treatment of diabetes. It can also be used to test for hepatitis, ulcers and certain cancers, including leukemia. RIA tests can also detect the presence of human growth hormone, a substance that has been banned for use by professional and amateur athletes.
The RIA technique can also be used for testing the presence of illegal narcotics in the bloodstream. Because it is relatively expensive, RIA is more commonly used by large public agencies, hospital systems, the federal government and the military. Private, smaller drug-screening firms generally use less expensive, although less accurate, methods. Banned or illegal substances cannot be masked in any way from the RIA method.