Cancer antigen 19-9 (CA 19-9) is a protein that exists on the surface of certain cancer cells. CA 19-9 does not cause cancer; rather, it is shed by the tumour cells and can be detected by laboratory tests in blood and sometimes other body fluids. This test measures the level of CA19-9.
Since CA 19-9 can be measured in blood, it is useful as a tumour marker to follow the course of cancer. CA 19-9 is elevated in about 70% to 95% of people with advanced pancreatic cancer. However, CA 19-9 may also be elevated in other cancers, conditions, and diseases such as: gallbladder and bile duct cancers (cholangiocarcinoma), colorectal cancer, gastric cancers, ovarian cancer, lung cancer, liver cancer, bile duct obstruction (e.g., gallstones), pancreatitis, cystic fibrosis, thyroid disease, and liver disease. Small amounts of CA 19-9 are present in the blood of healthy people. Since CA 19-9 is not specific for pancreatic cancer, it cannot be used by itself for screening or diagnosis.