CA-125 Blood Test (Ovarian Cancer)
The CA-125 blood test measures a tumor marker protein to help monitor ovarian cancer treatment or investigate pelvic growths.
What is a CA-125 blood test?
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—a substance often made by cancer cells or by normal cells in response to cancer.
Organs in the female reproductive system may make CA-125 when inflamed, which can happen during normal bodily functions like a menstrual period. However, high levels can also be a response to ovarian cancer.
What is it used for?
A CA-125 blood test can help your provider:
- See if ovarian cancer treatment is working or to check if ovarian cancer has come back. This is the most common use.
- Learn more about a growth or lump in your pelvis. If a suspicious lump appears on imaging, this test helps determine if it could be ovarian cancer.
- Screen for ovarian cancer if your risk is very high.
Providers generally do not use CA-125 to screen for ovarian cancer in those at average risk because other conditions—such as endometriosis, pelvic inflammatory disease, uterine fibroids, or liver disease—can also cause high levels.
Why do I need a CA-125 blood test?
You may need this test if you have been diagnosed with ovarian cancer, have a pelvic lump, or have a very high risk of ovarian cancer. High-risk factors include:
- A family history of ovarian, breast, or colorectal cancer.
- Inherited gene changes, such as in the BRCA 1 or BRCA 2 genes.
- Lynch syndrome.
- A personal history of breast, uterine, or colorectal cancer.
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. The process 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, such as slight pain or bruising at the needle site, which typically goes away quickly.
What do the results mean?
Your provider will review your results in the context of your overall health. Generally:
- During treatment: Decreasing levels usually indicate treatment is working; rising or stable levels may indicate it is not.
- After treatment: Increasing levels over time may suggest the cancer has returned.
- High-risk/Pelvic lump: High levels may be a sign of cancer, requiring further diagnostic testing.
Note: High CA-125 levels do not always mean cancer, and a normal result does not rule it out, as levels may be low in early-stage cancer.
Is there anything else I need to know about a CA-125 blood test?
If you have been treated for epithelial ovarian cancer, you may be tested for a tumor marker called HE4 along with CA-125, as measuring both can provide more accurate information.