Mayo Clinic Health Library

CA 125 test

Updated: 04-16-2011

Definition

A CA 125 test measures the amount of the protein CA 125 (cancer antigen 125) in your blood.

Many different conditions can cause an increase in CA 125. These include uterine fibroids, endometriosis, pelvic inflammatory disease and cirrhosis, as well as pregnancy and normal menstruation. Certain cancers, including ovarian, endometrial, peritoneal and fallopian tube, also can cause CA 125 to be released into the bloodstream.

A CA 125 test isn't accurate enough to use for cancer screening in all women — especially premenopausal women — because many benign conditions can increase the CA 125 level. What's more, CA 125 levels are normal in many women with early-stage ovarian cancer.

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Why it's done

You may have a CA 125 test for several reasons:

  • To monitor cancer treatment. If you've been diagnosed with ovarian, endometrial, peritoneal or fallopian tube cancer, your doctor may recommend a CA 125 test on a regular basis to monitor your condition and treatment. But such monitoring hasn't been shown to improve the outcome for women with ovarian cancer, and it might lead to additional and unnecessary rounds of chemotherapy or other treatments.
  • To screen for ovarian cancer if you're at high risk. If you've been identified as being at high risk of developing ovarian cancer due to a very strong family history of the disease or because you have the BRCA1 or BRCA2 gene mutation, your doctor may recommend a CA 125 test as one way to screen for the disease. There is no evidence that screening women with CA 125 decreases the chance of dying from ovarian cancer. An elevated level of CA 125 could prompt your doctor to put you through unnecessary and possibly harmful tests, so carefully discuss with your doctor the risks and benefits of having this test.
  • To check for cancer recurrence. Rising CA 125 levels may indicate that ovarian cancer has come back after treatment. Again, however, regular monitoring of CA 125 has not been shown to improve outcomes for women with ovarian cancer and may lead to additional and unnecessary rounds of chemotherapy or other treatments.

Your doctor may suggest a CA 125 test it's suspected that you have ovarian, endometrial, peritoneal or fallopian tube cancer. However, a CA 125 test cannot diagnose these diseases. Only a biopsy of tissue can confirm a diagnosis of these cancers. Other tests that may be helpful in evaluating these cancers include a transvaginal or pelvic ultrasound and computerized tomography (CT).

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How you prepare

If your blood is being tested only for CA 125, you can eat and drink normally before the test.

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What you can expect

For a CA 125 test, a member of your health care team takes a sample of blood by inserting a needle into a vein in your arm. The blood sample is sent to a lab for analysis. You can return to your usual activities immediately.

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Results

Results of the CA 125 test are measured in units per milliliter (U/mL). The normal range for CA 125 is less than 35 U/mL.

If your CA 125 level is higher than normal, your doctor will likely repeat the test. You may have a benign condition, or the test result could mean that you have ovarian, endometrial, peritoneal or fallopian tube cancer. But CA 125 is not a definitive diagnostic test for cancer, so your doctor will evaluate the results along with those of other tests that may be ordered.

If you've been previously diagnosed with ovarian, endometrial, peritoneal or fallopian tube cancer, a decreasing CA 125 level often indicates that the cancer is responding to treatment. A rising CA 125 level may indicate a return or continued growth of the cancer.

For specific information about what your CA 125 test results mean, talk with your doctor.

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