The cloned enzyme donor immunoassay (CEDIA) refers to an immunoassay that uses a genetically modified β-galactosidase enzyme. This enzyme has two units: an enzyme acceptor and an enzyme donor. These units alone are inactive, but they become activated and reassemble in solution. They can react with the substrate and change absorbance as a single unit. In CEDIA, reagent antibodies keep the enzyme subunits apart by physically blocking the binding of the monomer subunits from forming a tetramer. If there is a drug present in a patient sample, it will bind to the antibody and 'overwhelm' it, allowing the monomers to bind and enzyme activity to ensue. See the figure below for a depiction of the assay's mechanism of action.
