Chemiluminescent immunoassays (CIAs) also exploit the very strong and specific binding between an antibody and the epitope binding site on an antigen. Like EIAs, a CIA will have an immobilized capture protein (either an antigen or an antibody). The assay steps are then very similar to an EIA with the exception that instead of color production, or a change in fluorescence, the CIA uses reporter enzymes that produce light. The detection and quantitation for a CIA are performed using a luminometer (a component that measures photons) rather than a spectrophotometer or fluorometer (that measures absorbance or fluorescence respectively). CIAs are much more sensitive than EIAs. CIAs can detect concentrations of analytes with 1000Xs more sensitivity than traditional EIAs. For this reason, most high-volume serology tests are now performed using instruments that perform CIAs.
