Carcinoembryonic antigen (CEA) describes a set of highly related glycoproteins involved in cell adhesion. CEA is normally produced in gastrointestinal tissue during fetal development, but the production stops before birth. CEA are glycosyl phosphatidyl inositol (GPI) cell-surface-anchored glycoproteins whose specialized sialofucosylated glycoforms serve as functional colon carcinoma L-selectin and E-selectin ligands, which may be critical to the metastatic dissemination of colon carcinoma cells. Immunologically they are characterized as members of the CD66 cluster of differentiation. The proteins include CD66a, CD66b, CD66c, CD66d, CD66e (CEA), CD66f.Consequently, CEA is usually present at very low levels in the blood of healthy adults (about 2–4 ng/mL). The normal reference interval of serum CEA in Chinese adults was less than 5μg/L. However, the serum levels are raised in some types of cancer. CEA is an important tumor marker for colorectal and some other carcinomas. CEA is not a typical specific tumor marker, which needs to be combined with other indicators in clinical diagnosis to improve the specificity and sensitivity of detection.