ELISA: Enzyme-linked immunosorbent assay, a rapid immunochemical test that involves an enzyme used for measuring a wide variety of tests of body fluids. ELISA tests detect substances that have antigenic properties, primarily proteins rather than small molecules and ions, such as glucose and potassium. Some of these substances include hormones, bacterial antigens, and antibodies. ELISA tests are generally highly sensitive and specific, and they compare favorably with radioimmune assay (RIA) tests. They have the added advantage of not requiring the use of radioisotopes or radiation-counting apparatus.