Cancer antigen 125 (CA125) test
The cancer antigen 125 (CA125) test measures the amount of CA125 in the blood.
CA125 is a
CA125 levels can be higher than normal with certain non-cancerous (benign) conditions. They can also be higher when certain types of cancer are present, such as ovarian, fallopian tube and primary peritoneal cancers. Because ovarian, fallopian tube and primary peritoneal cancers can increase the level of CA125 in the body, CA125 is commonly used as a tumour marker for these types of cancer.
Why a CA125 test is done
Doctors mainly use CA125 tests to check how well ovarian cancer responds to treatment. They will use this test to measure the CA125 level in the blood before, during and after treatment.
If you haven’t been diagnosed with ovarian cancer but your doctor thinks you are at high risk or may have the disease, they may order a CA125 test. But the CA125 test can’t be used to screen for or diagnose ovarian cancer for these reasons:
- CA125 levels may be normal when ovarian cancer first develops, so the CA125 test may not be helpful in diagnosing it.
- CA125 levels can be higher than normal with certain non-cancerous conditions, such as endometriosis.
- Other types of cancer can increase CA125 levels.
How a CA125 test is done
A CA125 test is a blood test. A nurse or technologist will use a needle to take a sample of blood from a vein in your arm.
The blood is usually collected at a lab or hospital. You usually don’t need to do anything to prepare for it.
You may have several CA125 tests. Doing these tests over a period of time (called serial measurements) allows your healthcare team to check if cancer treatment is working.
What the results mean
Talk to your healthcare team about the results of a CA125 test and what they mean to you. Your doctor may recommend other tests or procedures, treatment or follow-up care.
These types of cancer can increase the level of CA125 in the blood:
- ovarian, fallopian tube and primary peritoneal
- uterine
- cervical
- pancreatic
- breast
- colorectal
- lung
- stomach
The following non-cancerous conditions can also increase the level of CA125:
- menstruation
- pregnancy
- endometriosis
- pelvic inflammatory disease
- ovarian cysts
- uterine fibroids
- liver disease
- inflammatory bowel disease
If your healthcare team is using a CA125 test to see how well the treatment for ovarian cancer is working, they will compare CA125 levels before, during and after treatment. But the CA125 level alone is not enough to confirm that treatment is working. If there are changes in the levels, your healthcare team may do other tests, such as an ultrasound or CT scan. These tests will give them more detailed information about the cancer and if it is responding to treatment.
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