radioimmunoassay

https://doi.org/10.1351/goldbook.R05105
An assay based on the reversible and non-covalent binding of an antigen (hapten) by a specific antibody employing radioactivity labelled antigen (hapten) to measure the fraction of the antigen (hapten) bound to a substoichiometric amount of antibody.
Source:
PAC, 1994, 66, 2513. 'Nomenclature for radioanalytical chemistry (IUPAC Recommendations 1994)' on page 2524 (https://doi.org/10.1351/pac199466122513)