CA-125 test

This page was reviewed under our medical and editorial policy by

Bradford Tan, MD, Chair, Department of Pathology and Laboratory Medicine, City of Hope Atlanta, Chicago and Phoenix.

This page was reviewed on November 15, 2021.

If your doctor is concerned about ovarian cancer, you may need to undergo a CA-125 test. This stands for cancer antigen 125, which is a glycoprotein found in the blood. Women with ovarian cancer sometimes have higher levels of CA-125, so it’s considered a tumor marker, or biomarker. If you’re scheduled to have a CA-125 blood test, here’s what to expect from the procedure.

What is a CA-125 test used for?

The CA-125 test is used for diagnosis and treatment.

For women already diagnosed with ovarian cancer, the test may be used to monitor treatment over time. Regular testing of CA-125 levels may indicate whether treatment is working successfully.

If you’ve completed active treatment for ovarian cancer, this test may be part of an ongoing surveillance routine to make sure the cancer hasn’t returned. If cancer has come back, it’s known as recurrent cancer.

If your care team suspects ovarian cancer, this test may be used to check for elevated CA-125 levels. However, the CA-125 test is most reliable in postmenopausal women who have a mass. It isn’t recommended as a general screening tool for women at average risk.

Postmenopausal women with elevated CA-125 levels may need additional testing, including a transvaginal ultrasound. This allows your doctor to see inside the pelvic area to check for ovarian cancer tumors.

Your doctor can explain in advance why the test is being administered and let you know when to expect your results.

CA-125 normal range

CA-125 levels in the body are measured by units per millimeter (U/mL).

The range of 0 to 35 U/mL is considered within the normal guidelines. Levels over 35 U/mL may indicate the presence of cancer or other conditions. Not all patients with a high CA-125 result have cancer.

For women with no ovarian cancer history, a high result usually leads to additional testing. In patients who’ve previously had ovarian cancer, high CA-125 levels may indicate a cancer recurrence.

Understanding test results

It’s normal to feel nervous or anxious before receiving your test results, but know that your care team can explain everything in detail. You can also ask questions at any time if you’re unsure about what’s being said.

Although the CA-125 test can be a good indicator of cancer, it has limitations. Not all women with ovarian cancer have elevated levels, which means it’s possible that some women with ovarian cancer will show low test levels. Increased CA-125 levels also don’t correspond to cancer stages, so a patient with advanced ovarian cancer won’t necessarily have a higher level than someone with early-stage cancer.

There are also health conditions other than cancer that may cause fluctuations in CA-125 levels, including:

  • Pregnancy
  • Endometriosis
  • Uterine fibroids

There is also some evidence to suggest that stress may cause your body to generate increased CA-125.

If you’re experiencing any of the above health conditions, including high levels of stress, tell your doctor before having your test done.

Your care team is the best source of knowledge for any specific questions relating to your test results. They can help you best understand your CA-125 levels, so you can make informed decisions about your health.

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