CA-125 Blood Test (Ovarian Cancer)
Reviewed
Also called: cancer antigen 125, glycoprotein antigen, ovarian cancer antigen, CA-125 tumor marker
This test measures the amount of a protein called CA-125 (cancer antigen 125) in a sample of your blood.
Specimen: blood sample from a vein in your arm
Why this test may be ordered
- To see if ovarian cancer treatment is working or to check if ovarian cancer has come back (most common use).
- To help evaluate a suspicious pelvic lump found on imaging, along with other tests.
- To screen for ovarian cancer if you have a very high risk (e.g., family history of ovarian, breast, or colorectal cancer; inherited BRCA gene changes; Lynch syndrome).
Preparation and collection
You don't need any special preparations for 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.
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.
Understanding results
Your provider will review your CA-125 test results along with other information about your condition.
- CA-125 going down during treatment for ovarian cancer: If you are being treated for ovarian cancer, and the results of several tests show that your CA-125 levels are going down, it usually means that the treatment is helping. Limitation: Some studies show that measuring both tumor markers provides more accurate information to check whether treatment is working and to look for the return of this type of cancer. Next step: Together, you can discuss how your results affect your diagnosis, treatment, and need for more testing.
- CA-125 going up or staying the same during treatment: If your levels go up or stay the same over time, it may mean that the treatment isn't working. Limitation: Some studies show that measuring both tumor markers provides more accurate information to check whether treatment is working and to look for the return of this type of cancer. Next step: Together, you can discuss how your results affect your diagnosis, treatment, and need for more testing.
- CA-125 increasing after finishing treatment: If you have finished your treatment for ovarian cancer and your CA-125 levels begin to increase over time, your cancer may be coming back. Limitation: Some studies show that measuring both tumor markers provides more accurate information to check whether treatment is working and to look for the return of this type of cancer. Next step: Together, you can discuss how your results affect your diagnosis, treatment, and need for more testing.
- High CA-125 with high risk or a suspicious pelvic lump: If you have a high risk for ovarian cancer or have a suspicious pelvic lump, high CA-125 levels could be a sign of cancer. Limitation: While high CA-125 levels don't always mean ovarian cancer, a normal CA-125 test result doesn't rule it out. Next step: Your provider will usually order more tests to make a diagnosis.
- High CA-125 levels do not always mean ovarian cancer; they can be caused by non-cancerous conditions such as endometriosis, pelvic inflammatory disease, uterine fibroids, liver disease, menstruation, and pregnancy.
- A normal CA-125 test result does not rule out ovarian cancer, because CA-125 levels may be low in the early stages of cancer, and not everyone with ovarian cancer makes high levels of CA-125.
- Only a biopsy can diagnose ovarian cancer.
What to do next
Talk with your provider if you have questions about your results.
- What is my personal risk for ovarian cancer based on my family history and other factors?
- What other tests might I need based on my CA-125 results?
- How often should I have this test if I am being treated for ovarian cancer or am at high risk?
Evidence source
Source: U.S. National Library of Medicine (MedlinePlus). Practices and reference ranges may differ in your country.
U.S. National Library of Medicine: CA-125 Blood Test (Ovarian Cancer)