Cancer Antigen 125 (CA-125) is a protein that is present on the surface of most, but not all, ovarian cancer cells. This makes the test useful as a tumor marker in specific circumstances. The CA-125 test measures the amount of CA-125 in the blood.
Significantly elevated concentrations of CA-125 may be present in the blood of a woman who has ovarian cancer. Thus the test may be used to monitor the effectiveness of treatment and/or for recurrence of the cancer. However, not all women with ovarian cancer will have elevated CA-125 so the test may not be useful in all cases.
Ovarian cancer is the fifth most common cause of cancer death in women. According to the American Cancer Society (ACS), the lifetime risk of a woman developing ovarian cancer is about 1 in 75 and the lifetime risk of death is 1 in 100. ACS estimates that about 22,000 new cases are diagnosed each year in the U.S. and about 14,000 women die of it.
Currently, less than 20% of ovarian cancers are found in the early stages before they have spread outside the ovary. The primary reason they go undetected is that the symptoms of ovarian cancer are fairly non-specific.
The need for a reliable method for early detection of ovarian cancer among asymptomatic women continues to drive ongoing research. In the meantime, regular physicals, pelvic exams, and an awareness of family history and symptoms are important.
CA-125 is not recommended as a screening test for asymptomatic women because it is non-specific. Small quantities of CA-125 are produced by normal tissues throughout the body and by some other cancers. Levels in the blood may be moderately elevated with a variety of non-cancerous conditions, including menstruation, pregnancy, and pelvic inflammatory disease.
If your blood is being tested only for CA 125, you can eat and drink normally before the test.
For a CA 125 test, a member of your health care team takes a sample of blood by inserting a needle into a vein, usually in your hand or arm. The blood sample is sent to a lab for analysis.
It's typically ordered every two to four months for the first two years following the completion of cancer treatment. After this period, the test is ordered every six months for three years and then once per year. Some doctors may recommend the CA-125 blood test to women with a strong family history of ovarian cancer.
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The blood test results should come through in a few days
Cancer antigen 125 (CA 125) is the only tumor marker recommended for clinical use in the diagnosis and management of ovarian cancer.
The reference range of CA 125 is 0-35 units/mL (0-35 kU/L).
If you are being treated for ovarian cancer, you may be tested several times throughout your treatment. If testing shows your CA-125 levels have gone down, it usually means the cancer is responding to treatment. If your levels go up or stay the same, it may mean the cancer is not responding to treatment.
If you have finished your treatment for ovarian cancer, high CA-125 levels may mean your cancer has come back.
If you are not being treated for ovarian cancer and your results show high CA-125 levels, it can be a sign of cancer. But it may also be a sign of a noncancerous condition, such as:
- Endometriosis, a condition in which tissue that normally grows inside the uterus also grows outside the uterus. It can be very painful. It may also make it harder to get pregnant.
- Pelvic inflammatory disease (PID), an infection of a woman's reproductive organs. It's usually caused by a sexually transmitted disease, such as gonorrhea or chlamydia.
- Uterine fibroids, noncancerous growths in the uterus
- Liver disease
- Menstruation, at certain times during your cycle
If you are not being treated for ovarian cancer, and your results show high CA-125 levels, your health care provider will probably order more tests to help make a diagnosis. Talk to your health care provider if you have questions about your results.
A CA-125 blood test measures the amount of cancer antigen 125 in the bloodstream. The protein is produced by the cells and can be found in the blood. A CA-125 blood test may be used to monitor ovarian cancer during and after treatment.
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.