Radioimmunoassay

Encyclopedia : R : RA : RAD : Radioimmunoassay

Radioimmunoassay is a scientific method used to test antigens (for example, hormone levels in the blood) without the need to use a bioassay. It involves mixing known quantities of radioactive antigen (frequently labeled with gamma-radioactive isotopes of iodine attached to tyrosine) with antibody to that antigen, then adding unlabeled or "cold" antigen and measuring the amount of labeled antigen displaced.

Initially, the radioactive antigen is bound to the antibodies. When "cold" (unlabeled, quest) antigen is added, the two compete for antibody binding sites - at higher concentrations of "cold" antigen, more of it binds to the antibody, displacing the radioactive variant. The bound antigens are separated from the unbound ones. The latter stay in the supernatant, the radioactivity of which is measured and a binding curve is plotted.

The technique is both extremely sensitive and specific, but it requires special precautions (because radioactive substances are used), sophisticated apparatus, and is expensive.

In medicine it is especially useful in diagnosing and treating autoimmune diseases such as Hashimoto's thyroiditis and Systemic Lupus Erythematosus.

It was developed by Rosalyn Yalow and Solomon Aaron Berson in the 1950s.

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