CEA (carcinoembryonic antigen) and Ca 19-9 (Carbohydrate antigen 19-9) are two blood tests commonly used to follow patients with known cancers. CEA is a glycoprotein (sugar protein) present in embryonic tissues and in extracts from normal colonic washings. CA 19-9 is a modified blood group antigen (Lewis(a)). Neither test should be used as a cancer screening test of asymptomatic individuals. Although CEA and/or levels are often elevated in patients with gastrointestinal malignancies (colon, pancreas, etc), patients with confirmed cancers frequently have normal levels (in the range of healthy individuals). Elevations in CEA and CA 19-9 levels may occur in patients without cancer. For example, elevated CEA levels may be observed in smokers as well as patients with a variety of non-malignant diseases. Therefore, levels, regardless of their values cannot be used as a diagnostic test for cancer. The greatest value of these tests is in detecting recurrence of malignancy (cancer) after treatment of the tumor. Finally, remember that the normal values of these tests differ from lab to lab. Values obtained from one lab cannot be directly compared to those obtained from another lab.