What is CA 125 test? What is a tumor marker?
CA 125 is a protein that is a so-called tumor marker or biomarker, which is a substance that is found in greater concentration in tumor cells than in other cells of the body. In particular, CA 125 is present in greater concentration in ovarian cancer cells than in other cells. It was first identified in the early 1980s, and the function of the CA 125 protein is not currently understood. CA stands for cancer antigen. CA 125 is often measured as a blood test.
How is CA 125 measured?
CA 125 is usually measured from a venous blood sample. It can also be measured in fluid from the chest or abdominal cavity. The tests currently in use are all based upon the use of an antibody that is directed against the CA 125 protein (monoclonal antibody technique).
In 1991, an improved version of the test was introduced and is sometimes denoted as CA 125 - II. The numerical figure of the second generation test results may be higher or lower than a first generation test. The first generation test is no longer used. When comparing multiple CA 125 test results over time, it can be important to know which method was used.
What is the normal range for CA 125?
The normal values for CA 125 may vary slightly among individual laboratories. In most laboratories, the normal value is 0 to 35 units/ml.
Ovarian Cancer Testing
The CA-125 is a blood test that is often, but not always, elevated with ovarian cancer. If a postmenopausal woman has a mass and an elevated CA-125, she has an extremely high risk of having a cancer. However, in younger women, CA-125 is extraordinarily inaccurate. It is elevated by a large number of disease processes, including but not limited to, diverticulitis, pregnancy, irritable bowel syndrome, appendicitis, liver disease, stomach disease, and more. No one should get this test done unless they actually have a mass, or their doctor has some reason to get it. It should not be drawn just to see the level since it is not a reliable screening test for ovarian cancer.
What does an elevated CA 125 level indicate, and how is the CA 125 test used?
It is not possible to interpret the meaning of abnormally high CA 125 results without additional information about the particular patient being evaluated. The reason is that blood levels of this protein can be increased in many different benign and malignant conditions, and an elevated level does not mean that cancer is present. CA 125 is used most often to monitor patients with a known cancer (malignancy) or as one of several tests in the workup of a patient suspected of having a tumor.
The most common use of the test is the monitoring of people with a known cancer that elevates CA 125 level, such as ovarian cancer. Around 75% to 85% of women with epithelial ovarian cancer will have an elevated CA 125 level. In the patient who is known to have a malignancy, such as ovarian cancer, the CA 125 level can be monitored periodically. A decreasing level generally indicates that therapy, including chemotherapy, has been effective, while an increasing level indicates tumor recurrence. Because of normal test variation, small changes are usually not considered significant. A doubling or halving of the previous value would be important.
In the patient who is being evaluated for a pelvic mass, a CA 125 level greater than 65 is associated with malignancy in approximately 90% of cases. However, without a demonstrable mass, the association is much weaker.
What conditions other than ovarian cancer can cause increased CA 125 results?
A number of benign conditions can cause elevations of the CA 125 level, including pregnancy, endometriosis, uterine fibroids (benign tumors), pancreatitis, normal menstruation, pelvic inflammatory disease, and cirrhosis of the liver. Benign tumors or cysts of the ovaries can also cause an abnormal test result. Increases can also be seen in cancers other than ovarian cancer, including malignancies of the uterine tubes, endometrium, lung, breast, pancreas, and gastrointestinal tract as well as lymphoma.
Is CA 125 testing useful as a cancer screening test?
Although CA 125 is a useful test in monitoring women who are being treated for ovarian cancer, a single CA 125 test is not considered to be a useful screening test for cancer. Some women with ovarian cancer (up to 20%) never have elevated CA 125 levels, while most women who do have elevated CA 125 levels do not have cancer. In fact, because the results of CA 125 testing can be elevated in so many noncancerous conditions, only about 3% of women with elevated CA 125 levels have ovarian cancer.
How much does the CA 125 test cost? Does insurance cover CA 125 testing?
The retail price for the test is approximately $150, although this can vary widely among laboratories. As with any test, insurance coverage depends upon many factors, including the reasons the test is being ordered and the patient's medical history. The test is typically covered when it is ordered for monitoring ovarian cancer and may be covered for additional settings. Patients should ask their physician and contact their insurance company with any questions they may have about coverage.
Medically Reviewed on 2/7/2018
King, G.G.T. "CA 125." Medscape.com. Oct. 30, 2015. <http://emedicine.medscape.com/article/2087557-overview>.