CA 19-9

Does this test have other names?

Cancer antigen 19-9, CA 19-9 radioimmunoassay (RIA) test

What is this test?

This test looks for the antigen called CA 19-9 in your blood.

Antigens are substances that stimulate your body's immune system. Certain types of cancer cells release the CA 19-9 antigen into the blood, where it can be measured with this test.

A high amount of CA 19-9 is most commonly caused by pancreatic cancer, but it can also be caused by the other cancers and by infections in your liver, gallbladder, and pancreas.

Antigens like CA 19-9 that give information about cancer are called tumor markers. This test is not used as a screening test for cancer.

Why do I need this test?

You may need this test if your doctor suspects that you might be at risk for cancer because of your symptoms or because you have a family history of cancer. You may need this test as part of your diagnosis along with other tests.

You may also need this test if you are having cancer treatment. It may be repeated every week or so to see how well treatment is working.

You may also need this test if you have already been treated for cancer and your doctor wants to find out whether your cancer has come back.

This test works best to help diagnose or make decisions about treatment for pancreatic cancer, but it may also be used for other cancers.

What other tests might I have along with this test?

Your doctor may also order tests to check for other tumor markers. Your doctor may also order imaging scans or other blood tests to learn about your cancer or to see whether you may have a noncancerous condition that causes a positive CA 19-9 blood test.

What do my test results mean?

Many things may affect your lab test results. These include the method each lab uses to do the test. Even if your test results are different from the normal value, you may not have a problem. To learn what the results mean for you, talk with your health care provider.

Results are given in units per milliliter (U/mL). Normal results are less than 37 U/mL.

It's important to know that higher levels of CA 19-9 don't mean you have cancer. Other conditions can cause higher levels.

Here is what your results may mean:

  • If your CA 19-9 is less than 37 U/mL, you may not have cancer.

  • If your CA 19-9 is above 37 U/mL, you may have cancer of the pancreas, liver, gallbladder, lung, colon, or stomach.

  • If your CA 19-9 is higher than normal but is less than 75 U/mL, you may have an infection of your pancreas, an infection of your gallbladder, liver disease, gallstones, or a disease called cystic fibrosis.

If you have been diagnosed with pancreatic cancer and your doctor is using this test as part of your treatment, here is what your results may mean:

  • If your CA 19-9 is going up during treatment, it may mean that the treatment is not working yet.

  • If your CA 19-9 is going down during treatment, it may mean that the treatment is helping you.

  • If your CA 19-9 went down after treatment but later goes back up, it may mean that your cancer has come back.

How is this test done?

The test requires a blood sample, which is drawn through a needle from a vein in your arm.

Does this test pose any risks?

Taking a blood sample with a needle carries risks that include bleeding, infection, bruising, or feeling dizzy. When the needle pricks your arm, you may feel a slight stinging sensation or pain. Afterward, the site may be slightly sore.

What might affect my test results?

Having radiation therapy for cancer when you have this test may give a false-positive result even if your treatment is working.

How do I get ready for this test?

You don't need to prepare for this test.