a technique for analyzing, and measuring the concentration of, antibodies, hormones, etc. in the body, used in diagnosing disease, detecting the presence of a tumor or drug, etc.
See immunoassay in American Heritage Dictionary 4
(ĭmˌyə-nō-ăsˈā, ĭ-myo͞oˌ-)
noun
A laboratory technique that makes use of the binding between an antigen and its homologous antibody in order to identify and quantify the specific antigen or antibody in a sample.