Chemiluminescent assays are the most popular assay currently in use due to their high sensitivity. These assays use antibodies that are conjugated to enzymes, such as peroxidase or alkaline phosphatase. These enzymes, when mixed with chemiluminescent substrates, produce light in the visible spectrum.
A direct relationship exists between the amount of drug that is present in the sample and the light units that are produced. This is measured by a luminometer in the instrument. Assays that use chemiluminescence are more sensitive than immunoassays that rely on the generation of a colored product.