CA 125

What is CA 125?

CA 125 (cancer antigen 125) is a glycoprotein produced in many tissues, such as the lining of the uterus, the fallopian tubes and the cells that line the membranes of the abdomen, chest and heart. A small amount of CA 125 can also be measured in people who have no disease. Its level in the blood can rise when there is inflammation, irritation or cell proliferation in these tissues.

Because the CA 125 level rises in a significant proportion of ovarian cancers, this test is used as a tumor marker. However, tumor markers are not screening or diagnostic tools on their own; CA 125 can rise in many benign conditions and may be normal in early-stage tumors. In the laboratory, CA 125 is measured in serum using automated antibody-based methods.

When is the CA 125 test ordered?

The main use of CA 125 is to monitor the response to treatment in people diagnosed with ovarian cancer and to look for recurrence during follow-up after treatment. Doctors may also use this test when evaluating an ovarian mass detected on imaging, especially in postmenopausal women. It is not recommended as a general screening test for women who have no symptoms and no special risk.

For women who carry an inherited genetic change that increases the risk of ovarian cancer, the monitoring plan is determined through genetic counseling and the doctor's recommendation. CA 125 may be only one part of this plan.

• Monitoring the response to treatment during ovarian cancer treatment
• Regular follow-up after treatment
• Further evaluation of an ovarian mass detected on ultrasound
• Evaluation the doctor considers necessary for complaints such as persistent bloating, feeling full quickly or pelvic pain
• Monitoring planned by the doctor for women at high familial risk

How should you prepare for the CA 125 test?

The CA 125 measurement is not affected by whether you have eaten or fasted. Because the level can rise temporarily during menstruation, it is preferable to have the test outside your period unless your doctor advises otherwise. Pregnancy, endometriosis, recent abdominal surgery and the use of biotin (vitamin B7) supplements can also affect the result and should be mentioned. For postmenopausal women, there is no need to time the test according to the menstrual cycle.

A few milliliters of blood drawn from an arm vein are enough for the sample. Because different measurement methods can give different results, it is recommended that measurements be done in the same laboratory as far as possible so that follow-up values can be reliably compared. You do not need to go to a hospital for the blood draw; a nurse can come to your home or workplace to take the sample.

What does the CA 125 result mean?

A high CA 125 does not by itself mean cancer. The level can also rise in many benign conditions, such as menstruation, pregnancy, endometriosis, fibroids, ovarian cysts, pelvic infections, liver disease, heart failure and fluid buildup in the lining of the abdomen or chest. Because such causes are more common in premenopausal women, the result is interpreted with care.

In people monitored for ovarian cancer, values that fall with treatment usually indicate a positive response, while a rise seen in consecutive measurements during follow-up may require further evaluation by the doctor. A normal result does not completely rule out disease either. Reference ranges may vary by method, laboratory, age and sex; you can see the testing laboratory's range on this page. It is your doctor's role to evaluate what your result means, together with your symptoms and your examination and imaging findings.