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The page below is a sample from the LabCE course Drug Testing Methods in the Clinical Toxicology Laboratory. Access the complete course and earn ASCLS P.A.C.E.-approved continuing education credits by subscribing online.

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Immunoassay Techniques Used in Drug Test Screening: Cloned Enzyme Donor Immunoassay (CEDIA)

Cloned enzyme donor immunoassay (CEDIA) refers to the genetically formulated enzyme β-galactosidase. This enzyme has two units; an enzyme acceptor and an enzyme donor. These units alone are inactive, but in solution, they become activated and reassemble. As a single unit, they can react with the substrate. Drug bound to the enzyme donor competes with the drug or metabolite in the sample for the antibody binding site. If the drug bound to the enzyme donor binds to the antibody, it is prevented from reassembling with the enzyme acceptor and activating the enzyme. If the drug or metabolite is present in the urine sample, the unbound enzyme donor reassembles with the enzyme acceptor and reacts with the substrate to produce a change in absorbance.