Carbohydrate antigen 19-9 (CA19-9) test

The carbohydrate antigen 19-9 (CA19-9) test measures the amount of CA19-9 in the blood.

CA19-9 (also called sialyl Lewis-a) is a protein that is normally found in small amounts in the body. It is made by cells in the pancreas, liver and gallbladder. It can also be found on certain types of cancer cells.

The CA19-9 level can be higher than normal with certain non-cancerous (benign) conditions. It can also be higher when certain types of cancer, including pancreatic and biliary tract cancers, are present. Because some types of pancreatic and biliary tract cancers can increase the level of CA19-9 in the body, CA19-9 is commonly used as a tumour marker for these cancers.

Doctors mainly use CA19-9 tests to check how well certain types of pancreatic and biliary tract cancer respond to treatment and to see if cancer has come back (recurred) after treatment.

The CA19-9 test can't be used by itself to screen for or diagnose pancreatic or biliary tract cancer for these reasons:

• About 5% to 22% of people don't produce CA19-9, so the test can't be used for them.
• The CA19-9 level can be higher than normal with certain non-cancerous conditions, such as inflammation of the pancreas (called pancreatitis) or a bile duct obstruction.
• Other types of cancer can increase the CA19-9 level.

A CA19-9 test is a blood test. A nurse or technologist will use a needle to take a sample of blood from a vein in your arm.

The blood is usually collected at a lab or hospital. You usually don't need to do anything to prepare for it.

Talk to your healthcare team about the results of a CA19-9 test and what they mean to you. Your doctor may recommend other tests or procedures, treatment or follow-up care.

These types of cancer can increase the level of CA19-9:

• pancreatic and biliary tract
• colorectal
• stomach
• esophageal
• lung
• liver
• ovarian
• bladder
• uterine

A very high level of CA19-9 is most commonly seen in people with advanced pancreatic cancer. Sometimes, jaundice can cause a very high level of CA19-9. The jaundice must be treated before a CA19-9 test can accurately interpret the CA19-9 level.

The following non-cancerous conditions can increase the level of CA19-9 in the blood:

• liver diseases, such as cirrhosis or hepatitis
• inflammation of the gallbladder (called cholecystitis) or gallstones
• bile duct obstruction or infection
• inflammation of the pancreas (called pancreatitis)
• cystic fibrosis
• some disorders of the lung, thyroid or gastrointestinal tract

If your healthcare team is using a CA19-9 test to check if treatment for pancreatic or biliary tract cancer is working, they will watch the CA19-9 level over time and compare any changes.

• If the CA19-9 level decreases or returns to normal, it may mean that the cancer is responding well to treatment.
• If the CA19-9 level doesn't change or increases, it may mean that the cancer is not responding well to treatment, is still growing or has come back.