Radioimmunoassay (RIA)

Introduction

• Definition — Radioimmunoassay (RIA) is the original member of the immunoassay family — assays that use the specific molecular-recognition binding of antibodies (or receptors/ligands) to capture, detect and measure an analyte — distinguished by a radioactive label on the detection reagent.
• Synonym — Immunoassays are equivalently termed ligand-binding assays (LBA); RIA is the radioisotopic prototype of this whole class.
• Why it matters — Clinical pharmacology — therapeutic drug monitoring and drug development alike — depends on accurate measurement of drug/metabolite/biomarker concentrations; immunoassays are the principal platform for large molecules (proteins, monoclonal-antibody drugs).
• Place among platforms — Small drug molecules → chromatographic methods (HPLC, LC-MS/MS); large therapeutics → immunoassays/LBA (the RIA family); RNA/DNA therapeutics → PCR assays.