An assay based on the competition between labeled and unlabeled ligand for the reactive sites of a particular substance
This assay is used to measure the concentration of biologically specific receptors in a sample. One example of its use it to measure antibodies in a sample by radioimmunoassay wherein a radioactively labeled antigens are introduced to bind to specific antibodies. The radioactivity in the products is then compared with the standard reaction to quantify antibodies.
The use of this assay extends to measuring other compounds that can be coupled with antigens, such as drugs, enzymes, and hormones.