In an immunoassay, what does the term "competition" refer to?

In the context of an immunoassay, the term "competition" refers to the availability of the analyte for binding sites. This is a fundamental concept in competitive immunoassays, where the analyte of interest competes with a labeled version of the same analyte for binding to specific antibodies.

During the assay, a fixed amount of antibody is provided, and as the concentration of the analyte increases, it binds to the antibody, reducing the amount of labeled analyte that can bind. Therefore, the extent of binding is inversely related to the concentration of the analyte in the sample. This competition is critical for the quantitative measurement of the analyte, as it allows scientists to determine the concentration of the target substance based on how much of the labeled analyte was able to bind to the antibody.

Understanding competition in this sense helps clarify the mechanics of quantitative detection in immunoassays, making it a key concept in this area of study.