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 your blood. CA-125 is a tumor marker that can be elevated in ovarian cancer, but also in non-cancerous conditions such as endometriosis, pelvic inflammatory disease, uterine fibroids, liver disease, menstruation, and pregnancy. The test is most commonly used to monitor ovarian cancer treatment and check for recurrence. It is not used for general screening because high levels do not always mean cancer and normal levels do not rule it out.
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 this test.
A health care professional will take a blood sample from a vein in your arm using a small needle. 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. Together, you can discuss how your results affect your diagnosis, treatment, and need for more testing.
- CA-125 levels going down over time (during treatment for ovarian cancer): Usually means the treatment is helping. Limitation: Only a biopsy can diagnose ovarian cancer. Normal CA-125 does not rule out cancer, especially in early stages. Next step: Your provider will discuss how your results affect your treatment plan.
- CA-125 levels going up or staying the same over time (during treatment for ovarian cancer): May mean the treatment isn't working. Limitation: Only a biopsy can diagnose ovarian cancer. Normal CA-125 does not rule out cancer, especially in early stages. Next step: Your provider will discuss how your results affect your treatment plan.
- CA-125 levels increasing over time (after finishing treatment for ovarian cancer): Your cancer may be coming back. Limitation: Only a biopsy can diagnose ovarian cancer. Normal CA-125 does not rule out cancer, especially in early stages. Next step: Your provider will usually order more tests to make a diagnosis.
- High CA-125 levels (if you have a high risk for ovarian cancer or a suspicious pelvic lump): Could be a sign of cancer. Limitation: Only a biopsy can diagnose ovarian cancer. High levels can also be caused by non-cancerous conditions such as endometriosis, pelvic inflammatory disease, uterine fibroids, liver disease, menstruation, and pregnancy. 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. Your provider will review your CA-125 test results along with other information about your condition to determine the need for more testing.
- 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
U.S. National Library of Medicine: CA-125 Blood Test (Ovarian Cancer)