radioimmunoassay

Radioimmunoassay (RIA) is a medical procedure that uses radioactively labeled substances to measure the concentration of a specific substance, typically a hormone or drug, in a patient's blood or other bodily fluid. This technique is a type of immunoassay, meaning it relies on the binding of antibodies to antigens.1

In RIA, a known amount of radioactive antigen is mixed with a sample containing an unknown amount of the same antigen. Antibodies are then added, which will bind to both the radioactive and non-radioactive antigens. Because the antibodies have a limited binding capacity, the more unlabeled antigen present in the sample, the less radioactive antigen will be bound to the antibodies. By measuring the amount of radioactivity bound to the antibodies, doctors can determine the concentration of the substance in the original sample. This method has been crucial in medical diagnostics, particularly for measuring hormone levels.12