An elevated level of the protein CA 125 in the blood is a possible sign of ovarian cancer, according to Mayo Clinic. Many other conditions can also cause elevated CA 125 levels.
Ovarian cancer cells typically contain higher concentrations of CA 125 than normal cells, so an elevated CA 125 level is sometimes a sign of ovarian cancer, according to MedicineNet. Doctors test a patient's CA 125 levels by taking a blood sample or a sample of fluid from the chest or abdomen. A normal level of CA 125 is between 0 and 35 units per milliliter. A level of CA 125 above 65 correlates strongly with ovarian cancer.
Doctors do not recommend a CA 125 blood test for women who have an average risk of ovarian cancer because many conditions can cause high CA 125 levels, including normal menstruation, pregnancy, pelvic inflammatory disease and fibroids in the uterus, as reported by Mayo Clinic. Even some conditions affecting parts of the body other than the reproductive system, including diverticulitis and liver cirrhosis, can cause CA 125 levels to be higher than usual.
Doctors use the CA 125 blood test to monitor patients who already have an ovarian cancer diagnosis, as described by MedicineNet. Decreasing levels of CA 125 are a sign that treatment of the cancer is working.