A laboratory technique that uses antibodies linked to enzymes to detect and measure the amount of a substance in a solution, such as serum. The test is done using a solid surface to which the antibodies and other molecules stick. In the final step, an enzyme reaction takes place that causes a color change that can be read using a special machine. There are many different ways that an ELISA can be done. ELISAs may be used to help diagnose certain diseases. Also called enzyme-linked immunosorbent assay.