immunoradiometric assay involving two sets of antibodies, one of which is labelled, that combine with different immunoreactive sites of an antigen molecule.
Source:
PAC, 1994, 66, 2513. 'Nomenclature for radioanalytical chemistry (IUPAC Recommendations 1994)' on page 2520 (https://doi.org/10.1351/pac199466122513)