CA-125 blood 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 a doctor is concerned about ovarian cancer, the patient may need to undergo a CA-125 blood test. This stands for cancer antigen 125, 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 a patient is scheduled to have a CA-125 blood test, here’s what to expect from the procedure.

What is a CA-125 blood test used for?

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

Monitor treatment

For women 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.

Monitor for recurrence

If the patient has completed 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.

Assist in diagnosis for certain women

If the 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 the care team to see inside the pelvic area to check for ovarian cancer tumors.

The doctor can explain in advance why the test is being administered and let the patient know when to expect her results.

CA-125 normal range

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

A CA-125 normal range falls between 0 and 35 U/mL. 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 CA-125 blood test results

It’s normal to feel nervous or anxious before receiving test results, but the care team can explain everything in detail. The patient can also ask questions at any time if she's 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 some women with ovarian cancer may 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.

What causes fluctuations in CA-125?

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

  • Pregnancy
  • Endometriosis
  • Uterine fibroids
  • Pelvic inflammatory disease, or PID
  • Liver disease
  • A woman's menstrual period

Some evidence suggests stress may also cause the body to generate increased CA-125.

If the patient experiences any of the above health conditions, including high levels of stress, tell the care team before having this test done.

The care team is the best source of knowledge for any specific questions related to CA-125 test results. They can help the patient best understand her CA-125 levels, so she can make informed decisions about her health.

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