What Is the RIA Test?

RIA is a sensitive and accurate technique for measuring blood antigens.

Radioimmunoassay, or RIA, is a technique used in testing for the presence of antigens (such as insulin and other hormones) in the bloodstream. The test dates to the 1950s; since that time many new applications for RIA have been developed. Because it uses radioactive materials and tests using radioactive reactions, RIA requires specialized equipment, as well as knowledgeable and careful handling. It is accurate and extremely sensitive, and it is also a relatively expensive method of testing.

Preparing the Sample

The lab technician mixes a sample of a fixed, known quantity of 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 antibody.

Separation

Blood serum from the patient is then added to the sample. The unbound antigen in the 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.

Measurement

The technician then 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.

Medical Uses

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 can detect the presence of human growth hormone, a substance that has been banned for use by professional and amateur athletes.

Screening Uses

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.

References

• DiscoveriesInMedicine: Radioimmunoassay
• AntibodyAndBeyond.com: Radioimmunoassay
• Radioimmunoassay