What is a Competitive ELISA?

In a competitive ELISA, a reference antigen is bound to the bottom of the microplate well, and the sample antigen competes with the reference antigen for binding to a specific antibody. When more antigen is present in the sample, less antibody binds to the reference antigen, resulting in a lower signal.

This format is commonly used when the target antigen is small or when only a single antibody is available. Signal intensity is inversely proportional to the amount of antigen present in the sample.