Radioimmunoassay: review of basic principles.

The development of radioimmunoassay by the late Solomon A. Berson and Rosalyn S. Yalow during the late 1950s represents a milestone in the history of the application of radionuclide methodology to biology and to medical investigation and practice. The method offers a technique to assay materials otherwise unmeasureable or detectable only with difficulty. Radioimmunoassay is based upon the competition between labeled and unlabeled antigen for specific antibody sites, forming antigen-antibody complexes. This reaction is described by the expression see journal for formula. At equilibirum, the radioactive complex (bound) is separated from the radioactive antigen (free). The B/F ratio is dependent upon the amount of nonradioactive antigen. Antigen concentration in unknown samples is determined by comparing the B/F ratio to the B/F ratios obtained by incubating varying amounts of known nonradioactive antigen with the same amount of antibody as in the unknown sample under similar assay conditions. Sensitivity of the order of 10-12 moles/liter may be achieved through the preparation and use of a labeled antigen of high specific activity and the production and selection of antisera with appropriately high affinity constants. Specificity is dependent upon the ability of the antiserum to recognize subtle structural features of the antigen molecule. The ability to conveniently assay large numbers of samples with good precision has led to the application of this technique to quantitate substances (such as steroids) already measurable but by more cumbersome methods. Since the initial description of competitive binding radioassay techniques, there have been numerous contributions to its further development, refinement, and application. This article reviews the conception and development of this invaluable contribution to our understanding of health and disease.