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CA 125

Does this test have other names?

Cancer antigen 125, glycoprotein antigen, ovarian cancer antigen

What is this test?

This test looks for the protein CA 125 in your blood. CA 125 is higher in many women with ovarian cancer.

Because this protein can be measured with a blood test, health care providers may use this test to look for ovarian cancer in women who may be at high risk because of family history or symptoms. They may also use this test to see if treatment is working or to find out whether cancer is coming back after treatment.

CA 125 is also higher in some noncancerous conditions. This means that CA 125 is not a good blood test to screen all women for ovarian cancer.

Why do I need this test?

You may have this test if you have symptoms of ovarian cancer or a family history of it. This test may be done as part of your diagnosis.

You may also have this test if you have already been diagnosed with ovarian cancer and your doctor wants to see if treatment was effective. You may get this test done before and during treatment.

You may also have this test if you've already been treated for ovarian cancer and your doctor needs to find out if the cancer has returned. Measuring CA 125 is one of the best ways to figure out if ovarian cancer has come back after treatment.

What other tests might I have along with this test?

Your doctor will likely order other tests, depending on your stage of the disease. These include other blood tests and imaging studies, like an ultrasound, CT scan, or MRI.

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). A normal CA 125 result is less than 35 U/mL.

But it's important to know that having a higher CA 125 result doesn't mean you have cancer. Many conditions other than cancer, including inflammatory disease, recent surgery, fibroids, your menstrual cycle, or an ectopic pregnancy, can cause CA 125 to rise.

And having a normal CA 125 result doesn't mean you don't have ovarian cancer. Some women with early ovarian cancer have a normal CA 125 level.

One elevated or normal CA 125 test result is not as important as a series of CA 125 blood tests over time.

If you have a high CA 125 level, your doctor may recommend that you see a gynecologic oncologist, a cancer doctor who specializes in cancers of the female reproductive system.

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?

Pregnancy and your menstrual cycle can affect your results. Some drugs used to treat ovarian cancer can also affect your results.

How do I get ready for this test?

You don't need to prepare for this test.