CA 19-9

What is CA 19-9?

CA 19-9 (cancer antigen 19-9) is a carbohydrate structure produced by the cells lining digestive organs such as the pancreas, bile ducts, stomach and intestines. For this reason, a certain level is also measured in the blood of healthy individuals. When there is inflammation, blockage or a tumor in these organs, the amount in the blood can rise.

Its structure is related to the Lewis blood group system; Lewis antigen–negative people, who make up a small proportion of the population, cannot produce CA 19-9, and in these people the value remains low even if disease is present. CA 19-9 is a tumor marker and is not a screening or diagnostic test on its own. It is measured in a serum sample with automated analyzers that use special antibodies. In Lewis antigen–negative people, the doctor may use other markers, such as CEA, for monitoring.

When is the CA 19-9 test ordered?

CA 19-9 is used mainly in people diagnosed with pancreatic cancer to establish a baseline value before treatment, to monitor the response to treatment and for follow-up after treatment. In bile duct, stomach and colon cancers, it can also give the doctor additional information together with other markers. It is not recommended for pancreatic cancer screening in people without symptoms.

In people with marked jaundice, the value may be high because of the blockage, so doctors may prefer to repeat the measurement after bile flow has returned to normal. This measurement is then used as the reference point for later values.

• Monitoring the response to treatment in pancreatic cancer
• Supporting other findings in the follow-up of bile duct cancers
• Contributing to the evaluation of a pancreatic mass detected on imaging
• Use together with markers such as CEA in monitoring stomach or colon cancer
• Regular check-ups planned by the doctor after treatment

How should you prepare for the CA 19-9 test?

Having had breakfast is not a problem for the CA 19-9 test. Conditions such as gallstones, jaundice, pancreatitis or liver disease can raise the value markedly, so be sure to mention any such conditions. High-dose supplements containing biotin (vitamin B7) can affect some measurement methods, so if you take them, consult your doctor or the nurse before the sample is taken. Keeping your previous results makes it easier for your doctor to track changes in the values.

A standard blood draw from the arm is performed for the test. During monitoring, having all measurements done in a single laboratory that uses the same method makes it easier to notice real changes in the values. A nurse can take this blood sample for you at your home or workplace.

What does the CA 19-9 result mean?

A high CA 19-9 is not always a sign of cancer. The value can also rise in benign conditions such as blockage and inflammation of the bile ducts, gallstones, acute or chronic pancreatitis, cirrhosis and hepatitis; quite high results can be seen especially with blockages accompanied by jaundice. In these cases, the value usually falls once the blockage has been relieved.

In people monitored for pancreatic cancer, values that fall after treatment may indicate a positive response, while a rise seen on repeated measurements may indicate the need for further evaluation. A normal result does not rule out disease, especially in Lewis antigen–negative people. The accepted upper limit may vary by laboratory, method, age and sex; the testing laboratory's range is shown on this page. A doctor should interpret what your value means, together with your symptoms, imaging and other tests.