Carbohydrate antigen 19-9 (CA19-9)

CA19-9 is the common term for carbohydrate antigen sialyl Lewis a. It is a protein found on the surface of certain cancer cells. It may be found in the blood when it is shed by cancer cells.

CA19-9 is commonly used as a tumour marker for some types of cancer of the pancreas. But this test cannot be used by itself to find pancreatic or other cancers because:

• CA19-9 is also found in healthy adults in small amounts in the pancreas, liver, gallbladder and lungs.
• About 5% of people do not produce CA19-9, so this test cannot be used for them.
• The blood levels of this antigen may also be at a higher than normal level in healthy people and in people with non-cancerous conditions such as pancreatitis or bile duct obstruction.

A CA19-9 test is mainly used to:

• check a person’s response to treatment for some types of pancreatic cancer, especially advanced pancreatic cancer
• see if pancreatic cancer is still growing or has come back (recurred) after treatment

CA19-9 is usually measured by a blood test. The blood sample is sent to a lab to be tested.

A higher than normal level of CA19-9 can be found in healthy people and can also be found in people with non-cancerous and cancerous conditions.

Non-cancerous conditions include:

• liver diseases, such as cirrhosis or hepatitis
• inflammation of the gallbladder (cholecystitis) or gallstones
• inflammation of the pancreas (pancreatitis)
• cystic fibrosis
• some disorders of the lung, kidney or gastrointestinal tract

Types of cancer include:

• some types of pancreatic cancer
• colorectal
• stomach
• liver
• bile duct
• lung
• breast
• uterine
• ovarian

The highest levels of this antigen are most commonly seen in people with advanced pancreatic cancer. CA19-9 is not usually high in people with very early stages of the disease.

If CA19-9 levels have been higher than normal, a decrease in CA19-9 or a return to normal values may mean that the cancer is responding well to treatment. An increase may mean that the cancer is not responding well to treatment, is still growing or is coming back. A slight increase may not be important. The doctor compares the levels over time.

The doctor will decide if more tests, procedures, follow-up care or additional treatment is needed.