CA-125 is a test used to evaluate ovarian cancer treatment. CA-125 is a protein that is found more in ovarian cancer cells than in other cells. This protein enters the bloodstream and can be measured by a blood test.

There are two CA-125 tests: a first generation test and a second generation test. The second generation test is now more widely used and is generally more accurate.

Blood is typically drawn from a vein, usually from the inside of the elbow or the back of the hand. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.

Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

No preparation is necessary.

When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.

The test is often used to follow women who have been diagnosed with ovarian cancer and who have previously had high CA-125 levels. In these cases, the CA-125 test is a very good tool to determine if ovarian cancer treatment is working, and whether the cancer remains in remission after treatment.

The CA-125 test may also be done if a woman has symptoms or findings on ultrasound that suggest ovarian cancer.

However, in general, the CA-125 is not a good test to screen healthy women for ovarian cancer.

The normal values for a CA-125 depend on the lab running the test. In general, levels above 35 U/mL are considered abnormal.

Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.

The examples above show the common measurements for results for these tests. Some laboratories use different measurements or may test different specimens.

In a woman with known ovarian cancer, a rise in CA-125 usually means that the disease has progressed or recurred. A decrease in CA-125 usually means the disease is responding to treatment.

In a woman who has NOT already been diagnosed with ovarian cancer, an elevated CA-125 can mean a number of things. While it can indicate that she has ovarian cancer, it can also indicate other types of cancer, as well as several benign diseases such as endometriosis.

When used in healthy women, an elevated CA-125 usually does NOT mean ovarian cancer is present. The vast majority of healthy women with an elevated CA-125 do not have ovarian cancer (or any other cancer for that matter). The "false positive" rate for this group of women is high.

Any woman with an abnormal CA-125 test will need further tests, and sometimes invasive surgical procedures, to confirm the result. These additional tests all involve risks and anxiety.

Therefore, the CA-125 should not be considered an effective general screening test for ovarian cancer. Studies are underway to determine whether it might be effective when combined with other blood tests or radiologic studies.

Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.

Other risks associated with having blood drawn are slight but may include:

• Excessive bleeding
• Fainting or feeling light-headed
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken)

Dann RB, et al. Strategies for ovarian cancer prevention. Obstet Gynecol Clin North Am. 2007;34(4):667-686.

Goonewardene TI, et al. Management of asymptomatic patients on follow-up for ovarian cancer with rising CA-125 concentrations. Lancet Oncol. 2007;8(9):813-821.

National Comprehensive Cancer Network. NCCN Practice Guidelines in Oncology: Ovarian cancer. 2009; v2.