Chemiluminescence Immunoassay (CLIA) are very similar to Enzyme-linked immunosorbent assays (ELISA). However, Chemiluminescence Immuno Assays are considered to be far superior to the ELISAs in terms of sensitivity and speed of the assay. The main reason for that is the fact that ELISAs are based on colorimetric measurements or fluorescent reactions, while CLIAs employ the enzyme horseradish peroxidase (HRP) which is coupled to the specific antibodies reacting with the antigen of interest. The HRP in CLIAs produces a light of a specific wavelength, following the reaction with a specific substrate, the chemiluminescent signal. The detection limit is significantly lower than that for ELISA tests. This makes CLIAs useful for a number of research areas that have been inaccessible to this type of immunoassay, employing specific antibodies, due to concentrations of target proteins or chemicals lower than the detection limit for ELISAs. Another advantage is that CLIAs require less time and do not demand the use of certain harmful reagents, such as stopping reagents. The intensity of the signal is proportional to the amount HRP enzyme bound via primary antibodies, which is proportional to the amount of target substance in the sample. The sensitivity and detection range far exceeds that of the average ELISA test.