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CA 125 Blood Test (Ovarian Cancer)

What is a CA-125 blood test?

This test measures the amount of a protein called CA-125 (cancer antigen 125) in the blood. CA-125 levels are high in many women with ovarian cancer. The ovaries are a pair of female reproductive glands that store ova (eggs) and make female hormones. Ovarian cancer happens when there is uncontrolled cell growth in a woman's ovary. Ovarian cancer is the fifth most common cause of cancer death in women in the U.S.

Because high CA-125 levels can be a sign of other conditions besides ovarian cancer, this test is not used to screen women at low risk for the disease. A CA-125 blood test is most often done on women already diagnosed with ovarian cancer. It can help find out if cancer treatment is working, or if your cancer has come back after you have finished treatment.

Other names: cancer antigen 125, glycoprotein antigen, ovarian cancer antigen, CA-125 tumor marker

What is it used for?

A CA-125 blood test may be used to:

  • Monitor treatment for ovarian cancer. If CA-125 levels go down, it usually means the treatment is working.
  • Check to see if cancer has come back after successful treatment.
  • Screen women who are at high risk for ovarian cancer.

Why do I need a CA-125 blood test?

You may need a CA-125 blood test if you are currently being treated for ovarian cancer. Your health care provider may test you at regular intervals to see if your treatment is working, and after your treatment is finished.

You may also need this test if you have certain risk factors for ovarian cancer. You may be at a higher risk if you:

  • Have inherited a gene that puts you at higher risk of ovarian cancer. These genes are known as BRCA 1 and BRCA 2.
  • Have a family member with ovarian cancer.
  • Previously had cancer in the uterus, breast, or colon.

What happens during a CA-125 blood test?

A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out. This usually takes less than five minutes.

Will I need to do anything to prepare for the test?

You don't need any special preparations for a CA-125 blood test.

Are there any risks to the test?

There is very little risk to having a blood test. You may have slight pain or bruising at the spot where the needle was put in, but most symptoms go away quickly.

What do the results mean?

If you are being treated for ovarian cancer, you may be tested several times throughout your treatment. If testing shows your CA-125 levels have gone down, it usually means the cancer is responding to treatment. If your levels go up or stay the same, it may mean the cancer is not responding to treatment.

If you have finished your treatment for ovarian cancer, high CA-125 levels may mean your cancer has come back.

If you are not being treated for ovarian cancer and your results show high CA-125 levels, it can be a sign of cancer. But it may also be a sign of a noncancerous condition, such as:

If you are not being treated for ovarian cancer, and your results show high CA-125 levels, your health care provider will probably order more tests to help make a diagnosis. Talk to your health care provider if you have questions about your results.

Is there anything else I need to know about a CA-125 blood test?

If your health care provider thinks you may have ovarian cancer, he or she may refer you to a gynecologic oncologist, a doctor who specializes in treating cancers of the female reproductive system.

References

  1. American Cancer Society [Internet]. Atlanta: American Cancer Society Inc.; c2018. Can Ovarian Cancer Be Found Early? [updated 2016 Feb 4; cited 2018 Apr 4]; [about 3 screens]. Available from: https://www.cancer.org/cancer/ovarian-cancer/detection-diagnosis-staging/detection.html
  2. American Cancer Society [Internet]. Atlanta: American Cancer Society Inc.; c2018. Key Statistics for Ovarian Cancer [updated 2018 Jan 5; cited 2018 Apr 4]; [about 4 screens]. Available from: https://www.cancer.org/cancer/ovarian-cancer/about/key-statistics.html
  3. American Cancer Society [Internet]. Atlanta: American Cancer Society Inc.; c2018. What Is Ovarian Cancer? [updated 2016 Feb 4; cited 2018 Apr 4]; [about 3 screens]. Available from: https://www.cancer.org/cancer/ovarian-cancer/about/what-is-ovarian-cancer.html
  4. Cancer.net [Internet]. Alexandra (VA): American Society of Clinical Oncology; 2005–2018. Ovarian, Fallopian Tube, and Peritoneal Cancer: Diagnosis; 2017 Oct [cited 2018 Apr 4]; [about 3 screens]. Available from: https://www.cancer.net/cancer-types/ovarian-fallopian-tube-and-peritoneal-cancer/diagnosis
  5. Lab Tests Online [Internet]. Washington D.C: American Association for Clinical Chemistry; c2001–2018. CA 125 [updated 2018 Apr 4; cited 2018 Apr 4]; [about 2 screens]. Available from: https://labtestsonline.org/tests/ca-125
  6. Mayo Clinic [Internet]. Mayo Foundation for Medical Education and Research; c1998–2018. CA 125 test: Overview; 2018 Feb 6 [cited 2018 Apr 4]; [about 3 screens]. Available from: https://www.mayoclinic.org/tests-procedures/ca-125-test/about/pac-20393295
  7. Mayo Clinic: Mayo Medical Laboratories [Internet]. Mayo Foundation for Medical Education and Research; c1995–2018. Test ID: CA 125: Cancer Antigen 125 (CA 125), Serum: Clinical and Interpretive [cited 2018 Apr 4]; [about 4 screens]. Available from: https://www.mayomedicallaboratories.com/test-catalog/Clinical+and+Interpretive/9289
  8. NOCC: National Ovarian Cancer Coalition [Internet] Dallas: National Ovarian Cancer Coalition; How am I Diagnosed with Ovarian Cancer? [cited 2018 Apr 4]; [about 4 screens]. Available from: http://ovarian.org/about-ovarian-cancer/how-am-i-diagnosed
  9. NOCC: National Ovarian Cancer Coalition [Internet] Dallas: National Ovarian Cancer Coalition; What is Ovarian Cancer? [cited 2018 Apr 4]; [about 2 screens]. Available from: http://ovarian.org/about-ovarian-cancer/what-is-ovarian-cancer
  10. National Heart, Lung, and Blood Institute [Internet]. Bethesda (MD): U.S. Department of Health and Human Services; Blood Tests [cited 2018 Apr 4]; [about 3 screens]. Available from: https://www.nhlbi.nih.gov/health-topics/blood-tests
  11. University of Rochester Medical Center [Internet]. Rochester (NY): University of Rochester Medical Center; c2018. Health Encyclopedia: CA 125 [cited 2018 Apr 4]; [about 2 screens]. Available from: https://www.urmc.rochester.edu/encyclopedia/content.aspx?contenttypeid=167&contentid=ca_125
  12. UW Health [Internet]. Madison (WI): University of Wisconsin Hospitals and Clinics Authority; c2018. Cancer Antigen 125 (CA-125): Results [updated 2017 May 3; cited 2018 Apr 4]; [about 8 screens]. Available from: https://www.uwhealth.org/health/topic/medicaltest/cancer-antigen-125-ca-125/hw45058.html#hw45085
  13. UW Health [Internet]. Madison (WI): University of Wisconsin Hospitals and Clinics Authority; c2018. Cancer Antigen 125 (CA-125): Test Overview [updated 2017 May 3; cited 2018 Apr 4]; [about 2 screens]. Available from: https://www.uwhealth.org/health/topic/medicaltest/cancer-antigen-125-ca-125/hw45058.html
  14. UW Health [Internet]. Madison (WI): University of Wisconsin Hospitals and Clinics Authority; c2018. Cancer Antigen 125 (CA-125): Why It is Done [updated 2017 May 3; cited 2018 Apr 4]; [about 3 screens]. Available from: https://www.uwhealth.org/health/topic/medicaltest/cancer-antigen-125-ca-125/hw45058.html#hw45065

The medical information provided is for informational purposes only, and is not to be used as a substitute for professional medical advice, diagnosis or treatment. Please contact your health care provider with questions you may have regarding medical conditions or the interpretation of test results.

In the event of a medical emergency, call 911 immediately.