Development and clinical application of sensitive enzyme immunoassay for macromolecular antigens--a review.

Radioimmunoassay has been a powerful tool to measure haptens and antigens which are important for the investigation and diagnosis of diseases, especially endocrine disorders. However, the use of radioisotopes in radioimmunoassay suffers from serious disadvantages. Radioisotope-labeled reagents are unstable and hazardous to health. The disposal of radioactive wastes is not easy. Furthermore, the sensitivity of radioimmunoassay is limited by the detection limit of radioisotope that depends upon the half-life. The detection limit of the most widely used radioisotope, 125I, with a half-life of 60 days is 5 to 10 amol, when it is carrier-free. By contrast, the use of enzymes has obvious advantages. Some enzymes are very stable and cause no health hazards or waste disposal problems, provided that appropriate substrates are chosen. The detection limits of some enzymes are lower than that of 125I and will be further improved in the future. Therefore, enzyme immunoassay is potentially more sensitive than radioimmunoassay. This article reviews the development and clinical application of sensitive enzyme immunoassay for macromolecular antigens, which has been replacing radioimmunoassay.