CA 19-9 is not sensitive or specific enough to be considered useful as a tool for cancer screening. Its main use is as a tumor marker: 

• to help differentiate between cancer of the pancreas and bile ducts and other non-cancerous conditions, such as pancreatitis; 
• to monitor a patient's response to pancreatic cancer treatment; and
• to watch for pancreatic cancer recurrence.

CA 19-9 can only be used as a marker if the cancer is producing elevated amounts of it; if CA 19-9 is not initially elevated, then it usually cannot be used later as a marker.

CA 19-9 may be ordered along with other tests, such as carcinoembryonic antigen (CEA), bilirubin, and/or a liver panel, when a patient has symptoms that may indicate pancreatic cancer, including abdominal pain, nausea, weight loss, and jaundice.

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

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

Moderate to high levels are found in pancreatic cancer, other cancers, and in several other diseases and conditions. The highest levels of CA 19-9 are seen in excretory ductal pancreatic cancer -- cancer that is found in the pancreas tissues that produce food-digesting enzymes and in the ducts that carry those enzymes into the small intestine. This tissue is where 95% of pancreatic cancers are found.

Serial measurements of CA 19-9 may be useful during and following treatment because rising or falling levels may give your doctor important information about whether the treatment is working, whether all of the cancer was removed successfully during surgery, and whether the cancer is likely returning.

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