Radioimmunoassay 1150897 224711672 2008-07-10T02:05:45Z Lightbot 7178666 Units/dates/other '''Radioimmunoassay''' (RIA) is a [[scientific method]] used to test [[antigen]]s (for example, [[hormone]] levels in the [[blood]]) without the need to use a [[bioassay]]. It involves mixing known quantities of [[radioactivity|radioactive]] [[antigen]] (frequently labeled with gamma-radioactive [[isotope]]s of [[iodine]] attached to [[tyrosine]]) with [[antibodies|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 [[concentration]]s of "cold" antigen, more of it binds to the antibody, displacing the radioactive variant. The bound antigens are separated from the unbound ones. One method of separation used initially was the use of a second antibody directed against the first for precipitation and centrifugation. The use of charcoal suspension for precipitation was extended but replaced later by Drs. Werner and Acebedo at Columbia University for RIA of T3 and T4.<ref>{{cite journal |author=Werner SC, Acebedo G, Radichevich I |title=Rapid radioimmunoassay for both T4 and T3 in the same sample of human serum |journal=J. Clin. Endocrinol. Metab. |volume=38 |issue=3 |pages=493–5 |year=1974 |pmid=4815178 |doi=}}</ref> An ultramicro RIA for human TSH was published in BBRC (1975) by Drs. Acebedo, Hayek et al.<ref>{{cite journal |author=Acebedo G, Hayek A, Klegerman M, Crolla L, Bermes E, Brooks M |title=A rapid ultramicro radioimmunoassay for human thyrotropin |journal=Biochem. Biophys. Res. Commun. |volume=65 |issue=2 |pages=449–56 |year=1975 |pmid=1148002 |doi=10.1016/S0006-291X(75)80168-9}}</ref> The free hormone stays in the [[supernatant]], the radioactivity of which is measured and a [[binding curve]] is plotted. The technique is both extremely [[sensitivity (tests)|sensitive]] and [[Specificity (tests)| specific]], but it requires special precautions (because radioactive substances are used), sophisticated apparatus, and is expensive. The technique has been largely replaced by the [[ELISA]] method where instead of a radioactive signal, the antigen-antibody reaction is measured by [[colorimetry|colorometric]] signals. The RIA was developed by [[Rosalyn Yalow]] and [[Solomon Berson|Solomon Aaron Berson]] in the 1950s.<ref>Yalow RS, Berson SA. Immunoassay of endogenous plasma insulin in man. ''J Clin Invest'' 1960;39:1157-75. PMID 13846364.</ref> [[Rosalyn Sussman Yalow]] received the 1977 [[Nobel Prize in Medicine]] for the development of the RIA for insulin. The precise measurement of minute amounts of such a [[hormone]] was a key event in [[endocrinology]]. ==References== <references/> ==External links== * {{MeshName|Radioimmunoassay}} * [http://www.biotecnika.googlepages.com/radioimmunoassay.html Radioimmunoassay- procedure] * http://www.lib.mcg.edu/edu/esimmuno/ch4/radassay.htm {{Immunologic techniques and tests}} [[Category:Endocrinology]] [[Category:Experimental design]] [[Category:Radiobiology]] {{med-stub}} [[de:Radioimmunoassay]] [[es:Radioinmunoensayo]] [[ja:放射免疫測定]] [[ru:Радиоиммунный анализ]]