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What Is the Blood Test CA-125 For?

The blood test CA-125 measures the amount of a certain protein (cancer antigen125) in your blood. It is used to monitor certain types of cancers that most often affect women, particularly ovarian, endometrial and fallopian tube cancers. Certain conditions other than cancer may cause the level of this protein to rise. These include pelvic inflammatory disease, endometriosis and cirrhosis of the liver. Levels may even rise during pregnancy or menstruation.

  1. The Facts

    • The blood test CA-125 may be ordered by your doctor if you are at high risk of developing ovarian cancer due to a family history of the disease, or if you are exhibiting symptoms of ovarian cancer. It may also be ordered if your doctor suspects you have endometrial or cervical cancer. If you have been diagnosed with one of these types of cancer, this blood test may be ordered to monitor cancer treatment.

    The Test

    • If you have the CA-125 blood test, what do the levels mean? In general, most healthy women have values less than 35. The higher the value, the more likely you have a problem. Women who have ovarian cancer sometimes test in the hundreds or even thousands. See "Understanding CA-125 Levels" in the Resources section for more information on test results.

    Considerations

    • The CA-125 isn't always an accurate tool for early detection of ovarian cancer. A true positive result is returned on only about 50 percent of Stage I ovarian cancer patients. For stage II, III and IV ovarian cancer, the test returns a true positive about 80 percent of the time. Elevated levels can be a false positive, or can indicate ovarian cancer or another type of cancer. They can also indicate a benign tumor.

    Significance

    • According to the Ovarian Cancer National Alliance, one in 72 women will develop ovarian cancer, and one in 95 women will die from ovarian cancer. About 75 percent of ovarian cancer is diagnosed in an advanced stage, after the cancer has spread from the ovary. The survival rate of women with ovarian cancer is approximately 46 percent; however in women that are diagnosed at an early stage, the survival rate is 93 percent.

    Misconceptions

    • Although the CA-125 is a diagnostic tool for ovarian cancer, it is not recommended to be used alone to diagnose this deadly disease, because the rate of false positives is very high. About 20 percent of women with ovarian cancer don't have an elevated CA-125. More than one method of detection should be used as a precaution. Other diagnostic tools include physical exam, ultrasound and biopsy.

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