A variety of enzyme systems operate to reveal a colorimetric signal in an assy. Such examples include glucose oxidase, perioxide and tetramethyl benzidine (TMB) system, and a horseradish peroxidase (HRP) system.
Other label systems include colored latex microparticles (Bangs Laboratories, Indiana), fluorescent compounds, radioactive compounds or elements or immunelectrodes.
Assays can be heterogenous (i.e., requiring a separation step) or homogenous.
Two preferred assay for the screening of biological fluids are radioimmunoassay (RIA) an enzyme linked immunosorbent assay (ELISA) [Engvall, Meth. Immunol., 70:419-439 (1980); S.K. Pierce et al., J. Exp. Med., 144:1254-1262 (1976); P.Tijssen, “Practice and Theory of Enzyme Immunoassays”, Laboratory Techniques in Biochemistry and Molecular Biology, 15:9-21, 329-384 (Aug. 1985)