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CA 125

What is CA 125?

CA 125 is a protein that is a tumour marker or biomarker. CA stands for cancer antigen and CA 125 is a substance that is found in greater concentration in tumour cells than in other cells of the body. Some women with ovarian cancer tend to have raised levels of CA 125, and there is lots of research underway to try to verify whether a CA 125 test can help in early diagnosis of ovarian cancer, but more research is needed. A higher than normal level can also indicate other health problems.

How is CA 125 measured?

Levels of CA 125 are usually measured using a blood sample. It can also be measured in fluid taken from the chest or abdominal cavity.

Early CA 125 tests used the 'monoclonal antibody technique'. In 1996, an improved version of this test was introduced that is sometimes called CA 125 - II. When comparing multiple 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 depending on individual laboratories. In most labs, the normal value is less than 35 U/ml.

What does an elevated CA 125 mean, and how is the test used?

An abnormally high level of CA 125 requires additional information about the patient before a diagnosis can be made. This is because blood levels of this protein can be elevated in many different benign or malignant conditions. CA 125 is usually used to monitor patients already diagnosed with cancer - or as one of several tests carried out in a patient suspected of having a cancer.

The most common use of the test is the periodic monitoring of women with ovarian cancer. A decreasing level usually indicates that therapy, including chemotherapy, has been effective, while an increasing level may indicate a cancer has recurred.

What conditions other than ovarian cancer can cause an increased CA 125?

Bear in mind that a number of conditions can also cause elevation of CA 125 levels. They include pregnancy, endometriosis, uterine fibroids ( benign tumours), pancreatitis, normal menstruation, pelvic inflammatory disease and liver disease. Benign tumours or cysts of the ovaries can also cause abnormal test results. Increases of CA 125 can also be seen in cancers other than ovarian cancer, including malignancies of the uterine tubes, endometrium, lung, breast, pancreas and the gastrointestinal tract.

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. For example, only about half of women with ovarian cancer have raised levels of CA 125. So if the test is used alone, some women with ovarian cancer may be missed. This is known by doctors as a 'false negative' result.

Also, most women who do have elevated CA 125 levels do not have cancer. In fact, because CA 125 can be elevated in so many non-cancerous conditions, only about a small percentage of women with elevated CA 125 levels have ovarian cancer.

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WebMD Medical Reference

Medically Reviewed by Dr Rob Hicks on December 24, 2012

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