Competitive Binding Assay
Definition
An immunoassay format in which labelled and unlabelled forms of the same analyte compete for a fixed, limiting number of antibody binding sites. As unlabelled analyte concentration rises, the proportion of labelled analyte bound falls. The signal is inversely proportional to analyte concentration.
- Field
- Immunoassay design, radioimmunoassay context
- Mechanism
- Labelled and unlabelled analyte compete for limited binding sites
- Signal relationship
- Inversely proportional to analyte concentration
- Binding sites
- Fixed, limiting number
Common questions
Why must the number of binding sites be limiting for a competitive assay to work?+
If binding sites were in excess, both labelled and unlabelled analyte would bind without competing against each other, and the signal would not fall as unlabelled analyte increases, so a fixed, limiting quantity of antibody is what creates the competition the assay depends on.
What is a practical consequence of the inverse signal relationship?+
Interpreting results requires a calibration curve rather than a direct reading, and low analyte concentrations produce high signal while high concentrations produce low signal, which is the opposite of the intuitive expectation and a common source of interpretation error for newcomers to the method.
Related terms
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