What is a CA-125 blood test?

This test measures the amount of a protein called CA-125 (cancer antigen 125) in the blood. CA-125 levels are high in many women with ovarian cancer. The ovaries are a pair of female reproductive glands that store ova (eggs) and make female hormones. Ovarian cancer happens when there is uncontrolled cell growth in a woman's ovary. Ovarian cancer is the fifth most common cause of cancer death in women in the U.S.

Because high CA-125 levels can be a sign of other conditions besides ovarian cancer, this test is not used to screen women at low risk for the disease. A CA-125 blood test is most often done on women already diagnosed with ovarian cancer. It can help find out if cancer treatment is working, or if your cancer has come back after you have finished treatment.

Other names: cancer antigen 125, glycoprotein antigen, ovarian cancer antigen, CA-125 tumor marker

What is it used for?

A CA-125 blood test may be used to:

• Monitor treatment for ovarian cancer. If CA-125 levels go down, it usually means the treatment is working.
• Check to see if cancer has come back after successful treatment.
• Screen women who are at high risk for ovarian cancer.

Why do I need a CA-125 blood test?

You may need a CA-125 blood test if you are currently being treated for ovarian cancer. Your health care provider may test you at regular intervals to see if your treatment is working, and after your treatment is finished.

You may also need this test if you have certain risk factors for ovarian cancer. You may be at a higher risk if you:

• Have inherited a gene that puts you at higher risk of ovarian cancer. These genes are known as BRCA 1 and BRCA 2.
• Have a family member with ovarian cancer.
• Previously had cancer in the uterus, breast, or colon.

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. 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.

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 to having a blood test. You may have slight pain or bruise at the spot where the needle was put in, but most symptoms go away quickly.