The cancer antigen 125 (CA-125) is a protein in the human bloodstream and can be produced by cancerous and non-cancerous cells. It is measured by a laboratory blood test. CA-125 is most often elevated by ovarian, endometrial, peritoneal and Fallopian tube cancers, and a doctor may use the CA-125 blood test to monitor the progress of cancer treatments, to watch for cancer recurrence after treatments or as a diagnostic test to evaluate cancer symptoms. Because CA-125 test results can be misleading and false, the test is never used as the only test to diagnose cancer.
- Skill level:
Find CA-125 on your laboratory test report. The numerical result of the CA-125 test is listed next to the test's name.
Compare the CA-125 numerical result to the reference range, which is usually in parentheses to the right of the numerical result. If the result falls within the reference range, then the test result is normal.
Look for a highlighted or differently coloured numerical result and an "(H)" or "(L) next to the numerical result." If the CA-125 test result falls outside of the reference range and is considered abnormal, the numerical result will be highlighted or printed in a different colour or appear next to an "(H)" for "high result" or an "(L)" for "low result."
Speak with your doctor for interpretation of your CA-125 test results because multiple factors can cause a false high or false low CA-125 level. An abnormal CA-125 level requires further testing and evaluation by your health-care professional.
Tips and warnings
- Among the many factors that can cause an elevated CA-125 level are pregnancy, menstruation, pelvic inflammatory disease, cirrhosis of the liver and certain gastrointestinal diseases.
- Some individuals with ovarian cancer have a normal CA-125 level.
- Laboratory results should be discussed with your doctor.
- Reference ranges for tests may vary among laboratories.
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