Enzyme-Linked Immunosorbant Assay (ELISA) is a method for specific quantitation of compounds.
Its specificity, flexibility and reproducibility have lead to widespread use as a diagnostic tool. Although there are competitive ELISA formats, the majority of ELISA assays are direct, indirect, or sandwich assays. Depending upon the assay method used and the method of detection, ELISAs can detect microgram to fentogram levels of protein.