CA-125 Blood Test


What is the CA-125 blood test?

A CA-125 test is a blood test that measures the amount of the protein CA-125, also called cancer antigen 125, in a person’s body.

CA-125 is a type of biomarker, or a substance in the blood that may be a sign of a condition or disease. A high level of CA-125 can be a sign of cancer, particularly ovarian cancer.

However, the test can have both false positive and false negative findings. CA-125 levels can be normal even if a person has cancer, or they can be elevated in a patient who does not have cancer. For this reason, a CA-125 test is not an effective screening for ovarian cancer.

Sometimes, physicians will order a CA-125 test as part of an overall approach to monitoring certain types of cancer – especially during and after treatment for the disease.

It also can be helpful in the early detection of ovarian cancer in women who are at increased risk of getting the disease. This could include factors such as if an immediate family member had ovarian cancer, or if the woman had ovarian cancer in the past.

However, a CA-125 test is rarely useful for women with no symptoms and no risk factors.

Test Details

How is the CA-125 blood test given and what may the results mean?

The test involves taking a small sample of the patient’s blood for testing. Patients do not need to fast for this test.

Many things other than ovarian cancer can lead to a person having a “positive” test score. These can include a woman having fibroids in the uterus or if she is currently menstruating. Sometimes people will have a high score but may have other types of cancer, such as endometrial, peritoneal, and fallopian tube cancers.

If your doctor thinks you may have ovarian cancer, or thinks you are at increased risk of developing it, a CA-125 test would be just one piece of the approach to monitoring your condition.

Results and Follow-Up

What is the follow-up to the CA-125 blood test?

If your doctor does order a CA-125 test and the results are positive, he or she will likely order additional tests to learn more. These would include transvaginal ultrasounds and other imaging tests. He or she may also simply decide to repeat the CA-125 test later to see if any changes have occurred.

Last reviewed by a Cleveland Clinic medical professional on 04/30/2018.


  • The Centers for Disease Control. Public and Provider Awareness of a CA-125 Test as a Screen for Ovarian Cancer. ( Accessed 5/10/2018.
  • National Cancer Institute. Screening Tests. ( Accessed 5/10/2018.

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