The Bureau of Medical Devices of the Food and Drug Administration recently granted premarket approval of two new assay kits for carcinoembryonic antigen (CEA), manufactured by Abbott Laboratories, North Chicago, Ill. Until now, the only method of quantitating blood levels of CEA was a competitive-binding radioimmunoassay (RIA) developed and marketed by Hoffman-La Roche, Inc, of Nutley, NJ.
In the indirect Roche RIA, plasma is extracted with perchloric acid to isolate CEA from other proteins. When the amount of CEA in the blood is considerable, a direct plasma assay can be performed.
The newly approved assays use solid-phase double antibody sandwich techniques. Anti-CEA antibody is allowed to attach to a polystyrene surface, and it traps CEA when a heat-treated serum or plasma sample is added. Another antibody is then added that complexes to the CEA-solid-phase antibody combination, resulting in a "sandwiched" CEA protein. This final antibody can either be radioactively tagged