What is a CA 19-9 blood test?

A CA 19-9 test measures the amount of a protein called CA 19-9 (cancer antigen 19-9) in a sample of your blood. CA 19-9 is a type of tumor marker. Tumor markers are substances made by cancer cells or by normal cells in response to cancer in your body.

Healthy people can have small amounts of CA 19-9 in their blood. High levels of CA 19-9 are often a sign of pancreatic cancer. But high levels can also be a sign of other types of cancer or certain conditions that aren't cancer. For example, gallstones and cirrhosis of the liver can cause high CA 19-9 levels.

Because high levels of CA 19-9 can mean different things, the test is not used by itself to screen for or diagnose cancer or other diseases. But it can help monitor your cancer and check how well your treatment is working.

Other names: cancer antigen 19-9, carbohydrate antigen 19-9, CA 199 measurement, CA 19-9 radioimmunoassay (RIA)

What is it used for?

CA 19-9 blood tests may be used to:

• Monitor certain types of cancer and cancer treatment. CA 19-9 levels often go up as cancer grows and go down as tumors shrink.
• Help predict how cancer may behave over time.
• Check whether cancer has returned after treatment.
• Help diagnose certain cancers and other diseases when used with other tests.

Some people do not make CA 19-9 even when they have a cancer that usually produces high levels of CA 19-9. For these people, a CA 19-9 tumor marker test is not useful.

Why do I need a CA 19-9 test?

You may need a CA 19-9 blood test if you've been diagnosed with pancreatic cancer or another type of cancer that causes high CA 19-9. These include cancers of the:

• Bile duct
• Colon and rectum
• Stomach
• Ovaries
• Bladder

During cancer treatment, your health care provider may test you on a regular basis to see if your treatment is working.

After your treatment is complete, you may need to have CA 19-9 tests to check whether the cancer has come back. High levels of CA 19-9 may be one of the first signs that cancer cells are growing again.

What happens during a CA 19-9 blood test?

A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.

Will I need to do anything to prepare for the test?

Usually, you don't need any special preparations for a CA 19-9 blood test. But ask your provider to be sure. If you take certain vitamins, you may need to stop them before the test.

Are there any risks to the test?

There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.

What do the results mean?

If you're being treated for cancer, you may be tested several times during your treatment. Your provider will look at all your test results to see how your CA 19-9 levels have changed. Your results may show:

• Your levels of CA 19-9 are increasing. This may mean your tumor is growing, and/or your treatment is not working. More tests are usually needed to find out for sure.
• Your levels of CA 19-9 are decreasing. This may mean your tumor is shrinking and your treatment is working.
• Your levels of CA 19-9 have stayed the same. This may mean your disease is stable and hasn't gotten better or worse.
• Your CA 19-9 levels decreased after treatment, but increased later. This may mean your cancer has come back or grown. You'll need more tests to check whether cancer is really causing the higher level of CA 19-9.

If you don't have cancer but your test results show a high level of CA 19-9, you may not a health problem that needs treatment. Healthy people can have high CA 19-9 levels. But high levels may be a sign of a condition, such as:

• Pancreatitis, inflammation of the pancreas
• Gallstones
• Bile duct disease, including a blockage or infection
• Liver disease
• Cystic fibrosis

Talk with your provider about what your results may mean.

If your provider thinks you may have one of these conditions, you will probably need other tests to find out for sure.

Learn more about laboratory tests, reference ranges, and understanding results.

Is there anything else I need to know about a CA 19-9 test?

Labs use different methods to measure the amount of CA 19-9 in your blood sample. The test method can affect your results. If you're having regular tests to monitor cancer, it's important to have your tests done the same way, and usually in the same lab. This allows your provider to compare your results over time. Your test report usually says what method was used to measure your CA 19-9 levels. If you have any questions about how your tests are done, talk with your provider.