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Microbiology & Infection
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Currently under review
Pending specialist review and validation.
Cancer Antigen 125 is a protein, also known as MUC16, that can be released into the bloodstream from cells lining the ovaries and other tissues in the body. The CA-125 test measures the amount of this protein in your blood.
Doctors use this test most often in the care of people with known or suspected epithelial ovarian cancer. It can help with the assessment of a pelvic mass, and it is commonly used to monitor how treatment is working over time and to watch for signs that disease may be returning. CA-125 is not specific to cancer, and levels can rise with several noncancer conditions, so results are interpreted together with your symptoms, exam, and imaging.
CA-125 can be helpful when your clinician is trying to understand the cause of pelvic symptoms or a mass, and during and after treatment for ovarian cancer to follow trends over time. It may also support decisions about imaging, surgery, or other tests.
It is not recommended for routine screening in people at average risk because elevations can occur with benign conditions and some ovarian cancers may not produce much CA-125. Using it thoughtfully helps reduce unnecessary worry or procedures while still providing valuable information when combined with clinical findings and imaging.
A single CA-125 result rarely gives a complete picture on its own. Lower values do not completely rule out disease, and higher values do not automatically mean cancer. Many noncancer conditions, such as menstruation, endometriosis, pelvic infections, liver disease, or recent surgery, can increase CA-125. Your clinician will interpret your result in context and may compare it to prior results to see if it is stable, rising, or falling.
If your result is higher than expected, your care team may repeat the test after a short interval, consider timing it away from menstruation, or evaluate for other causes like inflammation or infection. Depending on your situation, next steps could include ultrasound or other imaging, additional blood tests, or referral to a specialist. If you are being treated for ovarian cancer, trends over time are often more informative than any single measurement.
Reference intervals vary by laboratory, analyzer, methodology, population, and units. The ranges shown here are for education only. Always interpret your results against the reference interval printed on your own lab report.
Active menstruation or endometriosis can raise CA-125 temporarily. When possible, timing the blood draw away from menses can reduce false alarms.
Pregnancy, especially early stages and the immediate postpartum period, can increase CA-125. Your clinician will interpret results with this context in mind.
Pelvic inflammatory disease, appendicitis, peritonitis, or recent abdominal surgery can elevate CA-125 due to irritation of the peritoneum.
Liver disorders and fluid in the abdomen can increase CA-125. Treating the underlying condition often normalizes the marker over time.
Not all ovarian cancers release much CA-125, and some other cancers can raise it. The test’s usefulness varies with tumor characteristics.
Different test methods and laboratories may yield small differences. Using the same lab over time helps with consistent trend tracking.
Chemotherapy, targeted therapy, or procedures that kill tumor cells can cause short-term changes. Your clinician may recheck after therapy cycles.
Recent gynecologic or abdominal procedures can transiently increase CA-125. Inform your clinician about recent operations or procedures.
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