A laboratory test that measures the level of carcinoembryonic antigen (CEA) in the blood. An increased amount of CEA may be found in the blood of people who have colon cancer or other types of cancer, certain other diseases, or who smoke. The amount of CEA in the blood may also help keep track of how well cancer treatments are working or if cancer has come back. CEA is a type of tumor marker. Also called CEA assay.