ELISA is an immunological technique which is used to detect the presence of an antibody or an antigen in a sample. A known amount of antigen is coated on a solid phase like that in the well of a polystyrene microtitre plate and sample containing specific antibodies is added in the wells to allow antigen-antibody binding. The immune complex thus formed is linked to an enzyme, which acts on a substrate to give a coloured reaction which is detected using ultramodern ELISA plate readers. Since ELISA technique utilizes enzyme labels to produce detectable signals, it is given the name Enzyme-Linked Immunosorbent Assay.

Chemiluminescence Immunoassay (CLIA) provides a sensitive, high throughput, fully automated immunological technique, which has revolutionized Immunodiagnostics. It measures the intensity of light emitted when the complex of antigen in the patient’s sample and the enzyme linked antibody react with chemiluminescent molecule (such as luminol) producing a weak signal. The enzyme component then provides signal amplification.