a sensitive immunological assay, making use of antibodies and radioactive labelling, for the detection and quantification of biologically important substances, such as hormone concentrations in the blood
radioimmunoassay in American English
(ˈreɪdioʊˌɪmjʊnoʊˈæseɪ; ˈreɪdioʊˌɪmjʊnoʊæˈseɪ)
US
noun
the technique of immunoassay in which radioactive tracers are introduced into the substance to be analyzed