CA-125 Blood Test

Overview

What is a CA-125 test?

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

CA-125 is a type of biomarker or a substance in your blood that may be a sign of a condition or disease. A high level of CA-125 can be a sign of ovarian cancer. Your ovaries are a pair of reproductive glands that store and release eggs and produce hormones.

A CA-125 test can have both false positive and false negative findings. CA-125 levels can be normal even if you have cancer (false negative), or they can be elevated when you don’t have cancer (false positive). For this reason, a CA-125 test isn’t an effective screening for ovarian cancer.

Instead, healthcare providers will order a CA-125 blood test as part of an overall approach to monitoring certain types of cancer, especially during and after cancer treatment.

Providers also use this test for the early detection of ovarian cancer in people who are at high risk. This could include factors such as if an immediate family member had ovarian cancer or if you have been found to have a genetic mutation or error that increases your risk of developing ovarian cancer. A CA-125 test isn’t useful for people with no symptoms or risk factors.

What cancers does CA-125 detect?

It doesn’t detect cancer. The CA-125 test is used during the diagnosis, treatment and monitoring of ovarian cancer in certain people. It’s also used for cancer in your fallopian tubes or peritoneum.

When should the CA-125 test be done?

A CA-125 blood test may be used to:

  • Measure if treatment for ovarian cancer is working. If your numbers go down over time, it usually means cancer treatment is working.
  • Monitor if ovarian cancer comes back after successful treatment. This is done every few months or every year, depending on when you finished treatment.
  • Screen people at high risk for ovarian cancer.
  • Help with the evaluation of a person who has symptoms of ovarian cancer or is suspected of having ovarian cancer.

Who should get a CA-125 blood test?

If your healthcare provider thinks you may have ovarian cancer or is currently treating you for ovarian cancer, a CA-125 test may be used to monitor your condition.

You may need a CA-125 test if you’re at increased risk for ovarian cancer. Some factors that put you at increased risk are:

  • You’re a carrier of the BRCA gene. A gene is a part of your DNA that contains information about how your body works.
  • You have a biological family member with ovarian cancer.
  • You’ve had ovarian cancer.

Test Details

How is the CA-125 blood test done?

The test involves taking a small sample of your blood for testing. You may feel a small prick or sting when the needle is placed in your arm. The blood draw should take a few minutes. There are no dietary restrictions before the test.

Do I need to prepare for the CA-125 test?

You don’t need to do anything to prepare for a CA-125 test.

Are there risks to a CA-125 blood test?

There is little risk involved with having your blood taken. Taking a blood sample from some people may be more difficult than others. In rare cases, infection or excessive bleeding occurs. More commonly, people feel lightheaded during blood draw or bruise at the puncture site afterward.

How common are false results?

Many things other than ovarian cancer can lead to a “positive” test score. Some other conditions that can increase CA-125 levels in your blood are:

Because high levels of CA-125 can show up in other conditions, a CA-125 test is only used in conjunction with other diagnostic tools.

Results and Follow-Up

What is a good CA-125 test result?

Your results should be interpreted by your healthcare provider. Acceptable ranges may vary, and different labs may use different tests. Generally, levels higher than 35 units per milliliter are considered irregular. However, high levels don’t mean you have cancer or that cancer has returned. Discuss your results with your provider to determine what it means and if additional testing is needed.

What do the results of a CA-125 blood test mean?

Your healthcare provider will discuss what your test results mean for you. Even if the test shows high CA-125 levels, further testing is needed to diagnose cancer. The result of one test alone isn’t usually helpful. Your provider will order CA-125 tests in a series so they can identify changes in levels.

If you have ovarian cancer, a high CA-125 reading may mean cancer has returned or progressed. A lower score may indicate treatment is working.

Your CA-125 levels don't correlate with how much cancer is in your body. More testing is needed to confirm the extent of your condition.

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

If your healthcare provider orders a CA-125 test and the results are positive, they’ll likely order additional tests to learn more. These could include transvaginal ultrasound or magnetic resonance imaging (MRI). They may also decide to repeat the CA-125 test later to see if the results change.

A note from Cleveland Clinic

A CA-125 test is just one tool healthcare providers use to measure if cancer treatment is working. It's also used to screen for cancer in people who are high risk. It shouldn’t be used for people who have no symptoms or risk factors for ovarian cancer. Talk to your provider about your concerns with the CA-125 test and what the results mean for your care. Only your healthcare provider should interpret your test results.

Last reviewed by a Cleveland Clinic medical professional on 07/12/2022.

References

  • American Cancer Society. Ovarian Cancer Early Detection, Diagnosis, and Staging. (https://www.cancer.org/content/dam/CRC/PDF/Public/8775.00.pdf) Accessed 7/12/2022.
  • Foundation for Women’s Cancer. CA 125 Levels: Your Guide. (https://www.foundationforwomenscancer.org/wp-content/uploads/FWC-CA-125-Levels-Your-Guide.pdf) Accessed 7/12/2022.
  • National Cancer Institute. Screening Tests. (https://www.cancer.gov/about-cancer/screening/screening-tests) Tumor Markers. (https://www.mayoclinic.org/tests-procedures/ca-125-test/about/pac-20393295) Ovarian, fallopian tube, and primary peritoneal cancer screening (PDQ) – Patient version. (https://www.mayoclinic.org/tests-procedures/ca-125-test/about/pac-20393295) Accessed 7/12/2022.
  • Zhang M, Cheng S, Jin Y, Zhao Y, Wang Y. Roles of CA125 in diagnosis, prediction, and oncogenesis of ovarian cancer. (https://pubmed.ncbi.nlm.nih.gov/33421585/) Biochim Biophys Acta Rev Cancer. 2021 Apr;1875(2):188503. Accessed 7/12/2022.

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