CA-125 Blood Test (Ovarian Cancer)

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.

Why this test is done

If you've been diagnosed with ovarian cancer, you may have several CA-125 blood tests:

• During your treatment to see if your cancer is going away.
• After your treatment, to check if your cancer has returned.

If you have a lump in your pelvis that could be ovarian cancer, your provider may use  a CA-125 test to help find out if it could be ovarian cancer. But only a biopsy can diagnose ovarian cancer.

If you have a very high risk of getting ovarian cancer, your provider may suggest checking your CA-125 levels. If they're high, you'll probably need more tests to find out if you have cancer. You're more likely to get ovarian cancer if you:

• Have a mother or sister, or two or more other relatives who've had ovarian cancer.
• Have family members who've had breast cancer or colorectal cancer (colon cancer).
• Have inherited certain gene changes or conditions that increase your risk of ovarian cancer, such as:
• Changes in your BRCA 1 or BRCA 2 genes.
• Lynch syndrome (also called hereditary non-polyposis colorectal cancer), an inherited disorder that increases the risk for many types of cancer.
• Have had breast, uterine (uterus), or colorectal cancer.

If you're concerned about getting ovarian cancer, talk with your provider about your risk.

How to prepare

You don't need any special preparations for a CA-125 blood test.

Sample type

Blood

Other names for this test

cancer antigen 125, glycoprotein antigen, ovarian cancer antigen, CA-125 tumor marker