Cancer Antigen 125 (CA-125)

	Test Overview
	Why It Is Done
	How To Prepare
	How It Is Done
	How It Feels
	Risks
	Results
	What Affects the Test
	What To Think About
	References
	Credits
	Audio articles:
	English
	Español

A cancer antigen 125 (CA-125) is a protein found on the surface of many ovarian cancer cells. It also can be found in other cancers and in small amounts in normal tissue. A CA-125 test measures the amount of this protein in the blood.

CA-125 is used as a tumor marker—which means the test can help show if some types of cancer are present. Most often, the CA-125 test is used to check how well treatment for ovarian cancer is working or to see if ovarian cancer has returned.

The test for cancer antigen 125 (CA-125) is used to:

• Check if treatment for cancer is working. If the level of CA-125 is going down, it usually means that the treatment is working.
• Check if cancer has returned.
• Check if the ovary is the main site of cancer in a woman. If a cancer is found at another site (metastatic cancer), a higher-than-normal CA-125 test result may mean that ovarian cancer is the main site. However, other types of cancer also can increase CA-125 levels.

The CA-125 test is not recommended as a screening test for ovarian cancer at this time. However, the CA-125 test and an ultrasound scan may be used to test women who have a high chance for ovarian cancer. Women have a high risk of ovarian cancer if they have a family history of ovarian cancer or certain changes (mutations) in their DNA (such as the breast cancer BRCA1 mutation).

You do not need to do anything before you have this test.

The health professional drawing blood will:

• Wrap an elastic band around your upper arm to stop the flow of blood. This makes the veins below the band larger so it is easier to put a needle into the vein.
• Clean the needle site with alcohol.
• Put the needle into the vein. More than one needle stick may be needed.
• Attach a tube to the needle to fill it with blood.
• Remove the band from your arm when enough blood is collected.
• Put a gauze pad or cotton ball over the needle site as the needle is removed.
• Put pressure to the site and then put on a bandage.

The elastic band around your upper arm may feel tight. You may feel nothing at all from the needle, or you may feel a quick sting or pinch.

There is very small chance of problems from having blood drawn from a vein.

• You may get a small bruise at the site. You can lower your chance of bruising by putting pressure on the site for several minutes.
• In rare cases, the vein may become swollen after the blood sample is taken. This condition is called phlebitis. You can use a warm compress several times a day to treat this.
• Ongoing bleeding can be a problem for people with bleeding disorders. Aspirin, warfarin (Coumadin), and other blood-thinning medicines can also make bleeding more likely. If you have bleeding or clotting problems, or if you take blood-thinning medicine, tell your health professional before your blood is drawn.

The cancer antigen 125 (CA-125) test measures the amount of the CA-125 protein in the blood. Normal CA-125 values may vary from lab to lab.

High values

• Conditions other than cancer that can cause high CA-125 values include:
  • Pelvic inflammatory disease (PID).
  • Endometriosis.
  • Uterine fibroids.
  • Liver disease (such as hepatitis or cirrhosis).
  • Pancreatitis.
  • The first trimester of pregnancy.
  • Certain times during the menstrual cycle.
  • Lupus.

• Types of cancer that can cause high CA-125 values include:
  • Ovarian cancer or cancer of the fallopian tubes or endometrium. Most women with an ovarian cancer lump that can be felt in the pelvic area have CA-125 values higher than 65 U/mL.
  • Cancer of the pancreas, stomach, esophagus, liver, breast, colon, or lung.
  • Cancers that have spread to the lining of the abdomen (peritoneum), including lymphoma. These types of cancers usually occur along with the buildup of fluid in the abdomen (ascites).

Results of a cancer antigen 125 test can be affected by:

• Medicines used to treat cancer.
• A recent radioactive scan, such as a bone scan.
• Belly surgery. The CA-125 test should be done at least 3 weeks after surgery.

• The cancer antigen 125 (CA-125) test cannot tell the difference between a cancerous (malignant) or noncancerous (benign) ovarian lump.
• The test for CA-125 may also be done on body fluids (other than blood) taken from the chest or stomach area.
• High values of CA-125 in a woman who has been treated for ovarian cancer may mean that the cancer has returned. Often the high CA-125 level is found many months before the return of cancer can be found in another way.
• Studies are being done to see if CA-125 can be used as a screening test for ovarian cancer. So far, there is not enough proof to show that this test works to find ovarian cancer early.

Other Works Consulted

• Chernecky CC, Berger BJ, eds. (2004). Laboratory Tests and Diagnostic Procedures, 4th ed. Philadelphia: Saunders.

• Pagana KD, Pagana TJ (2006). Mosby’s Manual of Diagnostic and Laboratory Tests, 3rd ed. St. Louis: Mosby.