What is Cancer Antigen 125?
Cancer antigen 125 (CA 125) is a protein. The protein is commonly found on cancer cells of the ovary, though it can be noted in other forms of cancer. Patients with ovarian cancer may be tested for CA 125 throughout treatment. Lowering levels of the protein, compared to the initial test results, are indicative of effective cancer treatment. Doctors will also order a CA 125 test regularly to make sure the ovarian cancer has not returned.

CA 125 tests should not be used as a means of screening for any form of cancer. Results can be reported as a false positive, but with the use of ultrasound and other diagnostic tools it can be used as a pretest for increased risk. If CA 125 levels are high and there is a family history of cancer, a BRCA test may be ordered.

Normal Value Range

  • Negative Pregnancy Adult: < 35 U/ml
  • Pregnancy Trimester One: 0 to 51.5 U/ml
  • Pregnancy Trimester Two: 0 to 30.8 U/ml
  • Pregnancy Trimester Three: 0 to 56.3 U/ml

If Cancer Antigen 25 levels are normal, there could still be a tumor.

Higher than normal levels of Cancer Antigen 25 may be associated with tumors on the fallopian tubes, epithelial ovarian carcinoma, adenocarcinoma (cervical), trophoblastic tumor, carcinoma (endometrial, GI tract or lung), kidney failure, ascites, pancreatitis, cirrhosis, non-malignant gastrointestinal diseases, fibroids (uterine), adenomyosis or PID (pelvic inflammatory disease).

< Laboratory Values During Pregnancy

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