CA-125 blood test
The CA-125 blood test measures the level of the protein CA-125 in the blood.
How to Prepare for the Test
No preparation is necessary.
How the Test will Feel
When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or a slight bruise. These soon go away.
Why the Test is Performed
CA-125 is a protein that is found more in ovarian cancer cells than in other cells.
This blood test is often used to monitor women who have been diagnosed with ovarian cancer. The test is useful if CA-125 level was high when the cancer was first diagnosed. In these cases, measuring the CA-125 over time is a good tool to determine if ovarian cancer treatment is working.
After surgery and chemotherapy, patients should have the test every 2 to 4 months for the first 2 years. This is followed by every 6 months for 3 years, and then yearly.
The CA-125 test may also be done if a woman has symptoms or findings on ultrasound that suggest ovarian cancer.
In general, this test is not used to screen healthy women for ovarian cancer when a diagnosis has not yet been made.
A level above 35 U/mL is considered abnormal.
Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different samples. Talk to your doctor about the meaning of your specific test results.
What Abnormal Results Mean
In a woman who has ovarian cancer, a rise in CA-125 usually means that the disease has progressed or come back (recurred). A decrease in CA-125 usually means the disease is responding to treatment.
In a woman who has not been diagnosed with ovarian cancer, a rise in CA-125 may mean a number of things. While it can mean that she has ovarian cancer, it can also indicate other types of cancer, as well as several diseases such as endometriosis, which are not cancer.
In healthy women, an elevated CA-125 usually does not mean ovarian cancer is present. Most healthy women with an elevated CA-125 do not have ovarian cancer, or any other cancer.
Any woman with an abnormal CA-125 test needs further tests. Sometimes surgery is needed to confirm the cause.
Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others.
Other risks associated with having blood drawn are slight but may include:
- Excessive bleeding
- Fainting or feeling light-headed
- Hematoma (blood accumulating under the skin)
- Infection (a slight risk any time the skin is broken)
Coleman RL, Ramirez PT, Gershenson DM. Neoplastic diseases of the ovary: screening, benign and malignant epithelial and germ cell neoplasms, sex-cord stromal tumors. In: Lentz GM, Lobo RA, Gershenson DM, Katz VL, eds.Comprehensive Gynecology. 6th ed. Philadelphia, Pa: Elsevier Mosby; 2012:chap 33.
National Comprehensive Cancer Network. NCCN Clinical Practice Guidelines in Oncology: Ovarian cancer: including fallopian tube cancer and primary peritoneal cancer. Version 2.2013. Available at: http://www.nccn.org/professionals/physician_gls/pdf/ovarian.pdf. Accessed November 11, 2013.
Yi-Bin Chen, MD, Leukemia/Bone Marrow Transplant Program, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Bethanne Black, and the A.D.A.M. Editorial team.