Cancer Treatment Centers of America

CA-125 test

A CA-125 test measures the amount of the cancer antigen 125 (CA-125) in a person’s blood. CA-125 is a protein that is a biomarker or tumor marker. It is found in greater concentration in cancer cells, particularly ovarian cancer cells.

Cancer types that can cause higher than normal levels of CA-125 include:

The CA-125 test helps doctors:

  • Monitor ovarian cancer and other cancers to determine if they are responding to treatment
  • Monitor patients with ovarian and other cancers post-treatment to check for cancer recurrence
  • To an extent, screen for ovarian cancer in women who are at high risk for developing the disease

For the test, a nurse or other clinician obtains a sample of the patient’s blood. The sample is sent to a laboratory for analysis to determine if the level of CA-125 is abnormal.

Normal levels of CA-125 tend to be less than 35 units per milliliter, but laboratories do vary with what they consider a normal range.

Patients who have previously treated for ovarian cancer that have elevated CA-125 levels may have a cancer recurrence. However, additional testing and surgery (in some cases) is necessary to confirm a recurrence.

It’s important to note, conditions other than cancer can cause higher levels of CA-125, including:

  • Uterine fibroids
  • Endometriosis
  • Lupus
  • Liver disease
  • Pancreatitis
  • Pelvic inflammatory disease
  • The first trimester of a pregnancy
  • Menstruation

Additionally, cancer medications, recent abdominal surgery or radioactive scans can alter CA-125 levels.

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