Radioimmunoassay (RIA)
Definition
An immunological quantification method developed in the late 1950s in which a radiolabelled antigen competes with unlabelled antigen for antibody binding sites. Highly sensitive but requires radioactive isotopes and specialised facilities.
- Developed
- Late 1950s
- Principle
- Competitive binding, labelled vs unlabelled antigen
- Label type
- Radioactive isotope
- Limitation
- Requires specialised radioactive-handling facilities
Common questions
Why has radioimmunoassay largely been replaced in forensic laboratories?+
Enzyme-linked and fluorescence-based immunoassays achieve comparable sensitivity without the licensing, disposal, and safety burden of handling radioactive isotopes, making them far more practical for routine casework.
What is the competitive-binding principle that makes RIA work?+
A fixed amount of antibody is exposed to a mixture of radiolabelled antigen and the unlabelled antigen from the sample, which compete for the same limited binding sites, so the amount of radioactivity that ends up bound falls as the sample's antigen concentration rises.
Related terms
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- Lateral-Flow Immunoassay
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- Monoclonal Antibody
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- Precipitin Test
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