Enzyme immunoassay (EIA) is a test used to detect and quantify specific antigen-eliciting molecules involved in biological processes, specifically processes related to cancer and autoimmune disorders. EIA can be used on most types of biological samples, such as plasma, serum, urine, and cell extracts. In the assay, a plate is coated with a primary antibody, which recognizes the antigen of the target molecule and bonds with it. The antigen-antibody complex is recognized by a secondary antibody that is joined to an enzyme that catalyzes the reaction mixture, yielding a specific color. By measuring the optical density of this color, the presence and number of a specific molecule can be determined; the density of color is proportional to the advancement of the reaction or disease being tested.
SUDHIR K. SRIVASTAVA
(SEE ALSO: Antibody, Antigen)