Enzyme immunoassay for carcinoembryonic antigen.

In this rapid, simple enzyme immunoassay for carcinoembryonic antigen (CEA) in serum the "sandwich" system is used. The CEA is first extracted from the serum into acetate buffer by heating at 70 degrees C, then incubated in a polyvinyl microtitration plate previously coated with anti-CEA. The bound CEA is then reacted with anti-CEA conjugated to horseradish peroxidase and the activity of the peroxidase bound to the wells of the plate is quantified by adding the enzyme substrate. The assay is sensitive to 3.1 micrograms/L (which can be improved to 0.39 microgram/L by prolonging the incubation times to 120 min), precise (between-assay CV 8.0%), and shows adequate analytical recoveries. Results compared favorably with those by a radioimmunoassay kit (Abbott Diagnostics), r = 0.99. The reference interval for serum CEA in normal adults is shown. This assay is appropriate for use in monitoring patients with colorectal tumors after surgery.