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 send the CA 19-9 antigen into the blood, where it can be measured with
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,
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 health care provider thinks 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 done 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 provider
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 health care provider may also order tests to check for other tumor markers. Your
provider may also order imaging scans or other blood tests to learn about your cancer.
These other tests can tell whether you may have a condition other than cancer 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
Results are given in units per milliliter (U/mL). Normal results are less than 37
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 health care provider 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
If your CA 19-9 is going down during treatment, it may mean that the treatment is
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
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.