Immunoassay

An immunoassay is a specific type of biochemical test that measures the presence or concentration of a substance (referred to as the "analyte") in solutions that frequently contain a complex mixture of substances. Analytes in biological liquids such as serum or urine are frequently assayed (i.e., measured) using immunoassay methods. In essence, the method depends upon the fact that the analyte in question is known to undergo a unique immune reaction with a second substance, which is used to determine the presence and amount of the analyte. This type of reaction involves the binding of one type of molecule, the antigen, with a second type, the antibody. Immunoassays can be carried out using either the antigen or the antibody in order to test for the other member of the antigen/antibody pair. In other words, the analyte may be either the antigen or the antibody.