Other
CA-125
Also known as: Cancer Antigen 125
About CA-125
This test measures the amount of a protein called CA-125 (cancer antigen 125) in a sample of your blood. CA-125 is a type of tumor marker. Tumor markers are substances that are often made by cancer cells or by normal cells in response to cancer.
Organs in the female reproductive system (such as the ovaries and fallopian tubes) may make CA-125 when those organs are inflamed. This may happen in response to normal bodily functions, such as a menstrual period. However, your body may also produce high levels of CA-125 in response to ovarian cancer.
The ovaries are a pair of female reproductive glands that store ova (eggs) and make female hormones. Ovarian cancer happens when the cells in an ovary begin to grow out of control.
Main source: MedlinePlus ↗
Useful for
See if ovarian cancer treatment is working or to check if ovarian cancer has come back. This is the most common use of CA-125 blood testing.
Learn more about a growth or lump in your pelvis (the area below your belly). If a suspicious lump shows up on imaging, such as an ultrasound, your provider may check your CA-125 levels along with other tests to find out whether the lump could be ovarian cancer.
Screen for ovarian cancer if your risk is very high. If your family health history includes ovarian cancer, your provider may suggest a CA-125 blood test and other tests to look for signs of cancer.
Main source: MedlinePlus ↗
Interpretation
Your provider will review your CA-125 test results along with other information about your condition. Together, you can discuss how your results affect your diagnosis, treatment, and need for more testing.
CA-125 is most useful for people already diagnosed with ovarian cancer. After surgery and chemotherapy, a CA-125 level that goes back to normal usually means treatment is working, and a level that stays high or rises over time often means the cancer is still active or coming back.
CA-125 is not very accurate for finding ovarian cancer at an early stage. It is raised in only about half of women with stage I disease, but in most women with more advanced disease. A normal CA-125 does not rule out ovarian cancer.
Many non-cancer conditions can also raise CA-125. These include endometriosis, pelvic inflammatory disease (PID), uterine fibroids, liver disease, and even your menstrual period or early pregnancy.
Because CA-125 can be high for many reasons, providers do not use it to screen people who are not at high risk for ovarian cancer.
Talk with your provider if you have questions about your results.
For general wellness information only. Talk to a clinician about your specific results.
Main source: MedlinePlus ↗
Track your ca-125 in MyBloodTest
Save reviewed lab results and follow their history. Scanning requires sign-in and has plan-specific limits.
Open the web app
iOS · Android · Web
Related biomarkers
More tests in the other category.
Sources
Last updated 2026-05-02
This page presents source-specific reference data and sourced explanations. For general wellness information only. This is not medical advice. For diagnosis or treatment of any condition, talk to a qualified clinician.