The CA 19-9 test may be used, along with other tests such as carcinoembryonic antigen (CEA), bilirubin, and/or a liver panel, to help evaluate and monitor a person who has been diagnosed with pancreatic cancer and is undergoing treatment.

CA 19-9 is used as a tumor marker:

• To monitor a person's response to pancreatic cancer treatment and/or cancer progression
• To watch for pancreatic cancer recurrence
• Sometimes to aid in the diagnosis of pancreatic cancer

CA 19-9 can only be used as a tumor marker if the cancer is producing elevated amounts of it. Since CA 19-9 is elevated in about 65% of those with bile duct cancer (cholangiocarcinoma), it may be ordered to help evaluate and monitor people with this type of cancer.

The CA 19-9 test is not sensitive or specific enough to use as a screening test for cancer. It is not currently useful for detection or diagnosis by itself because non-cancerous conditions can cause elevated CA 19-9 levels. Researchers continue to investigate markers to be used alone or in combination with CA 19-9 that may be more useful for screening for and detecting pancreatic cancer in the early stages, when it is most treatable.

CA 19-9 may be ordered when a person has been diagnosed with pancreatic cancer and/or has signs and symptoms that may indicate pancreatic cancer. Early signs and symptoms may be subtle and nonspecific. Examples include:

• Abdominal and/or back pain
• Nausea
• Loss of appetite
• Unexplained weight loss
• Jaundice

In later stages, there may be chronic pain, nausea, vomiting, malabsorption, and, in some rare instances, problems with blood glucose control.

If CA 19-9 is initially elevated in pancreatic cancer, then a series of CA 19-9 tests may be ordered during cancer treatment to monitor response and on a regular basis following treatment to help detect recurrence.

CA 19-9 may sometimes be ordered when a healthcare practitioner suspects bile duct cancer in a person with a bile duct obstruction. Non-cancerous causes of bile duct obstruction can cause very high CA 19-9 levels, which fall when the blockage is cleared. In these cases, it is a good idea to wait at least a week or two after the blockage is relieved (by placing a tube, or stent, in the bile ducts) to re-check CA 19-9 levels.

Low amounts of CA 19-9 can be detected in healthy people, and many conditions that affect the liver or pancreas can cause temporary elevations.

Moderate to high levels may be seen in people with pancreatic cancer, other cancers, and in several other diseases and conditions. The highest levels of CA 19-9 are seen in cancer of the exocrine pancreas. This cancer arises in the tissues that produce food-digesting enzymes and in the ducts that carry those enzymes into the small intestine. About 95% of pancreatic cancers are of this type.

Levels of CA 19-9 that are initially high and then fall over time may indicate that the treatment is working and/or that the cancer was removed successfully during surgery. Levels that remain high or rise over time may indicate that treatment is not working and/or that the cancer is recurring.

Unfortunately, early pancreatic cancer gives few warning signs. By the time a person has symptoms and significantly elevated levels of CA 19-9, pancreatic cancer is usually at an advanced stage.

CA 19-9 is a protein on the surface of cells. It is derived from a blood group antigen called Lewis antigen that is similar to the ABO antigens that are used in blood typing for transfusions. About 5% to 7% of people are Lewis antigen negative (about 30% in people of African ancestry) and do not produce CA 19-9. The CA 19-9 test is not useful for monitoring people who are Lewis antigen negative.

Laboratories may use different methods to test for CA 19-9, so results can vary from lab to lab. If you are having a series of CA 19-9 tests done, it is advised that you have the tests done by the same method, typically by the same laboratory, so that the results can be compared and interpreted correctly. You may wish to discuss this issue with your healthcare practitioner.