Why Is My Doctor Testing My Blood for CA 125?

Reviewed on 3/5/2021

CA 125 (cancer antigen 125) is a sugar-associated protein (glycoprotein) in the blood that is considered a biomarker (or “tumor marker”) because it is found in greater concentrations in ovarian cancer cells. Doctors test the blood for CA 125 to help diagnose ovarian cancer.
CA 125 (cancer antigen 125) is a sugar-associated protein (glycoprotein) in the blood that is considered a biomarker (or “tumor marker”) because it is found in greater concentrations in ovarian cancer cells. Doctors test the blood for CA 125 to help diagnose ovarian cancer.

Doctors test the blood for CA 125 to:

  • Help diagnose ovarian cancer in women at risk for developing ovarian cancer
  • Identify recurrent ovarian cancer in women who have been treated before
  • Help predict the outcome of treatment in women with ovarian cancer and other related cancers, such as fallopian tube and primary peritoneal cancers
  • Check how a woman is responding to treatment
  • Screen for ovarian, primary peritoneal, and fallopian tube cancers in high-risk women or in women with abnormal findings on examination or ultrasound
  • Use as a marker to determine the risk of malignancy before surgery

What Is CA 125?

CA 125 (cancer antigen 125) is a sugar-associated protein (glycoprotein) in the blood that is considered a biomarker (or “tumor marker”) because it is found in greater concentrations in ovarian cancer cells. 

What Level of CA 125 Indicates Cancer?

The normal range for CA 125 is 0 to 35 units/ml. While a CA 125 level over 35 may indicate cancer, it does not always mean the person has cancer. A CA 125 level over 35 is only a potential indicator. 

  • If a woman has not been previously diagnosed with ovarian cancer, high levels indicate further testing is needed to make a diagnosis. 
  • If a woman has been previously treated for ovarian cancer and CA 125 levels are high, it may mean cancer has returned. More tests would be needed to make an ovarian cancer diagnosis.
CA 125 Levels Chart
CA 125 Levels (units/mL) Potential Cancer
0 – 35 (normal) Unlikely to have cancer. 99% of the time, it means no cancer.
>35 (high) Possible cancer. More tests will be needed for a diagnosis.

What Are Limits of the CA 125 Test?

Limits of the CA 125 test include: 

  • CA 125 is only elevated in about 50% of women with early-stage ovarian cancer and 85% of women with advanced ovarian cancer, which means a woman may have ovarian cancer and levels of CA 125 may not be elevated
  • Levels of CA 125 do not correlate with the stage of cancer
  • Several noncancerous conditions can also cause an increase CA 125 levels, including: 
  • CA 125 measurements are not recommended for screening women with a low risk for developing ovarian cancer

QUESTION

Where does ovarian cancer occur? See Answer

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Reviewed on 3/5/2021
References
https://www.foundationforwomenscancer.org/wp-content/uploads/FWC-CA-125-Levels-Your-Guide.pdf

https://emedicine.medscape.com/article/2087557-overview

https://ocrahope.org/patients/about-ovarian-cancer/symptoms-and-detection/what-is-ca-125/