Radioimmunoassay

Radioimmunoassay is a scientific methodused to test antigens(for example, hormonelevels in the blood) without the need to use a bioassay. It involves mixing known quantities of radioactiveantigen(frequently labelled with gamma-radioactive isotopesof iodineattached to tyrosine) with antibodyto 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 concentrationsof "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 curveis ploted.

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

In medicineit is especially useful in diagnosing and treating autoimmune diseasessuch as Hashimoto's thyroiditisand Systemic Lupus Erythematosus.

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

This article is licensed under the GNU Free Documentation License.
It uses material from the http://en.wikipedia.org/wiki/Radioimmunoassay Wikipedia article Radioimmunoassay.