The instrument used is Beckman Coulter UniCel DXI 800. The Access CEA assay is a 2-site immunoenzymatic sandwich assay using mouse monoclonal anti-carcinoembryonic antigen (CEA) antibodies that react with different epitopes of CEA. A sample is added to a reaction vessel, along with the first anti-CEA monoclonal antibodies-alkaline phosphatase conjugate and the second anti-CEA monoclonal antibodies bound to paramagnetic particles. The incubation is followed by a magnetic separation and washing. The chemiluminescent substrate Lumi-Phos 530 is added to the vessel and light generated by the reaction is measured with a luminometer. The light production is proportional to the concentration of CEA in the sample. The amount of analyte in the sample is determined by means of a stored, multipoint calibrator curve.(Package insert: Access CEA Assay, Beckman Coulter, Inc, Fullerton, CA, 2007)
For all samples with CEA concentrations >3 ng/mL, a dilution series is performed. A linear dilution excludes hooking and most major interferences. Samples that contain CEA concentrations < or =3 ng/mL are spiked with exogenous CEA to identify possible interferences that may cause a false-low result.