• Also Known As:
  • CA 125 Tumor Marker
  • Formal Name:
  • Cancer Antigen 125
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At a Glance

Why Get Tested?

To monitor treatment for ovarian cancer or to detect recurrence of disease; sometimes to evaluate a lump located in the pelvic area (pelvic mass); not recommended for screening asymptomatic women but sometimes ordered to help detect early ovarian cancer in those identified as being at high risk

When To Get Tested?

Before starting therapy for ovarian cancer and at intervals during and after treatment; sometimes when you have a pelvic mass or are at a high risk for developing ovarian cancer

Sample Required?

A blood sample drawn from a vein in your arm

Test Preparation Needed?


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You may be able to find your test results on your laboratory’s website or patient portal. However, you are currently at Lab Tests Online. You may have been directed here by your lab’s website in order to provide you with background information about the test(s) you had performed. You will need to return to your lab’s website or portal, or contact your healthcare practitioner in order to obtain your test results.

Lab Tests Online is an award-winning patient education website offering information on laboratory tests. The content on the site, which has been reviewed by laboratory scientists and other medical professionals, provides general explanations of what results might mean for each test listed on the site, such as what a high or low value might suggest to your healthcare practitioner about your health or medical condition.

The reference ranges for your tests can be found on your laboratory report. They are typically found to the right of your results.

If you do not have your lab report, consult your healthcare provider or the laboratory that performed the test(s) to obtain the reference range.

Laboratory test results are not meaningful by themselves. Their meaning comes from comparison to reference ranges. Reference ranges are the values expected for a healthy person. They are sometimes called “normal” values. By comparing your test results with reference values, you and your healthcare provider can see if any of your test results fall outside the range of expected values. Values that are outside expected ranges can provide clues to help identify possible conditions or diseases.

While accuracy of laboratory testing has significantly evolved over the past few decades, some lab-to-lab variability can occur due to differences in testing equipment, chemical reagents, and techniques. This is a reason why so few reference ranges are provided on this site. It is important to know that you must use the range supplied by the laboratory that performed your test to evaluate whether your results are “within normal limits.”

For more information, please read the article Reference Ranges and What They Mean.

What is being tested?

Cancer Antigen 125 (CA-125) is a protein that is present on the surface of most, but not all, ovarian cancer cells. This makes the test useful as a tumor marker in specific circumstances. The CA-125 test measures the amount of CA-125 protein in your blood.

Significantly elevated concentrations of CA-125 may be present in the blood of a woman who has ovarian cancer. Thus, the test may be used to monitor the effectiveness of treatment and/or for recurrence of the cancer. However, not all women with ovarian cancer will have elevated CA-125 so the test may not be useful in all cases.

Ovarian cancer is the fifth most common cause of cancer death in women. According to the American Cancer Society (ACS), the lifetime risk of a woman developing ovarian cancer is about 1 in 78 and the lifetime risk of death is 1 in 108. ACS estimates that in 2019 about 22,530 women will be diagnosed with ovarian cancer in the U.S. and about 13,980 women will die of it.

Currently, less than 20% of ovarian cancers are found in the early stages before they have spread outside the ovary. The primary reason they go undetected is that the symptoms of ovarian cancer are fairly non-specific.

The need for a reliable method for early detection of ovarian cancer among asymptomatic women continues to drive ongoing research. In the meantime, regular physicals, pelvic exams, and an awareness of your family history and symptoms are important.

CA-125 is not recommended as a screening test for asymptomatic women because it is non-specific. Small quantities of CA-125 are produced by normal tissues throughout your body and by some other cancers. Levels in your blood may be moderately elevated with a variety of non-cancerous conditions, including menstruation, pregnancy, and pelvic inflammatory disease.


Common Questions

How is the test used?

CA-125 is a tumor marker primarily used to monitor therapy during treatment for ovarian cancer. CA-125 is also used to detect whether your cancer has come back after treatment is completed. A series of CA-125 tests that shows rising or falling levels is often more useful than a single result.

CA-125 is sometimes used along with transvaginal ultrasound to test and monitor women who have a high risk for ovarian cancer but who do not yet have the disease. The most significant risk factor for ovarian cancer is an inherited genetic variant in one of two genes: breast cancer gene1 (BRCA1) or breast cancer gene 2 (BRCA2) – see BRCA Gene Mutation Testing. Women with an inherited condition called Lynch syndrome may also have a higher risk of ovarian cancer (a lifetime risk of about 10%). Other risk factors are family history, increasing age, reproductive history and infertility, use of hormone replacement therapy, and obesity.

Sometimes a CA-125 test may be ordered along with a transvaginal ultrasound to help investigate a lump in woman’s lower abdominal area (pelvic mass.)

The test is not used, however, to screen women for ovarian cancer because it is non-specific. The U.S. Preventive Services Task Force recommends against screening women for ovarian cancer. This recommendation applies to asymptomatic women but not to women at high risk for developing ovarian cancer, such as those with a genetic mutation.

Currently, there is no one reliable method for early detection of ovarian cancer among asymptomatic women. Less than 20% of ovarian cancers are found in the early stages before they have spread outside the ovary. One reason they go undetected is that the symptoms of ovarian cancer are fairly non-specific. In the meantime, regular physicals, pelvic exams, and an awareness of your family history and other risk factors are important. (For more about ovarian cancer, see the “What is being tested?” section or the article on Ovarian Cancer.)

When is it ordered?

The CA-125 test may be ordered before you start ovarian cancer treatment as a baseline to compare against future measurements. During therapy, a healthcare practitioner may order CA-125 testing at intervals to monitor response to therapy. CA-125 may also be measured periodically after therapy is completed.

In some cases, a healthcare practitioner may order a CA-125 test when you have a pelvic mass in order to help determine the cause.

Some healthcare providers may order a CA-125 test and a transvaginal ultrasound at regular intervals when you are at high risk of developing ovarian cancer.

What does the test result mean?

  • If your CA-125 levels are initially high and then fall during therapy, this generally indicates that the cancer is responding to treatment.
  • If the CA-125 levels rise or stay the same, then your cancer may not be responding to therapy.
  • An initial fall of CA-125 levels after treatment is completed with a subsequent rise in CA-125 levels may indicate that your cancer has come back.

If you have been diagnosed with ovarian cancer and your baseline CA-125 level is normal, then the test is not likely to be useful to monitor your ovarian cancer. In this case, the ovarian cancer may not be producing CA-125 and is not a good marker of disease progression.

If you have a pelvic mass and are at a high risk for developing ovarian cancer, a significantly elevated CA-125 is a concern but does not necessarily indicate ovarian cancer. This finding would prompt further laboratory testing and clinical evaluation.

Why isn’t CA-125 used to screen for ovarian cancer?

Because CA-125 can be high in many normal or benign conditions, such as pregnancy, menstruation, endometriosis, and pelvic inflammatory disease, it is not useful or recommended as a screening test for the general population.

Are there other tumor markers used in ovarian cancer?

A new tumor marker, human epididymis protein 4 (HE4), may be ordered along with CA-125 to monitor epithelial cell tumors, the most common type of ovarian cancers. These cancers develop from the cells that cover the outside of the ovaries. The use and full clinical utility of this test has yet to be determined.

Is CA-125 always increased in ovarian cancer?

No, not all ovarian cancers are associated with increased levels of CA-125. Elevated levels have been found in about 80% of women with ovarian cancer.

Does ovarian cancer run in families?

Family history is a risk factor for ovarian cancer. If you have close family members who have had ovarian cancer, you are at higher risk than someone who has no family history of the disease. Make sure your healthcare providers know about your family medical history. Women who have inherited a mutation in one of the BRCA genes are at high risk of ovarian cancer. For more details, see the article on BRCA Gene Mutation Testing.

What are some other risk factors for ovarian cancer?

In addition to family history, other risk factors include increasing age, obesity, and use of hormone replacement therapy. See the American Cancer Society website for more on this.

View Sources

Sources Used in Current Review

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