Enzyme-linked immunosorbent assays (ELISA) are useful for measuring levels on antigens and antibodies. Both competitive and sandwich methods can be used. These assays are analogous to radioimmunoassays in format and have similar sensitivity. However, results can sometimes by read visually and even for objective readings only simple equipment is needed. ELISA has been used to measure hormones and other protein antigens and has also been used to assay antibody levels.