Current status of homogeneous enzyme immunoassays

Recent advances in homogeneous enzyme immunoassays (EIAs) are discussed. EIA methods have been developed with comparable sensitivity to those of radioimmunoassay (RIA). EIAs have become established in many clinical laboratories and are generally being employed for: 1) homogeneous assay of low molecular weight compounds such as drugs and antibiotics present in biological samples at relatively high concentrations, 2) qualitative and semiquantitative assays for viral, bacterial, fungal, and parasitic antigens and antibodies, 3) tissue immunohistochemical localization of antigens and antibodies, and 4) alternatives to RIA in smaller laboratories. This paper discusses the principles and applications of newer homogeneous assays such as avidin‐biotin enzyme, hybrid antibody, insoluble sub state and cloned enzyme donor, and electrochemical immunoassays. Future instrumentation for EIAs with the use of biosensors is also discussed.