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Cancer Antigen 125 (CA-125)


The cancer antigen 125 (CA-125) test measures the amount of the CA-125 protein in the blood.

The normal values listed here—called a reference range—are just a guide. These ranges vary from lab to lab, and your lab may have a different range for what's normal. Your lab report should contain the range your lab uses. Also, your doctor will evaluate your results based on your health and other factors. This means that a value that falls outside the normal values listed here may still be normal for you or your lab.

Cancer antigen 125 normal values1

Less than 35 units per milliliter (U/mL)

Less than 35 kiloUnits per liter (kU/L) (SI units)

High values

What Affects the Test

Results of a cancer antigen 125 test can be affected by:

  • Medicines used to treat cancer.
  • A recent radioactive scan, such as a bone scan.
  • Abdominal surgery. The CA-125 test should be done at least 3 weeks after surgery.

What To Think About

  • The cancer antigen 125 (CA-125) test cannot tell the difference between a cancerous (malignant) or noncancerous (benign) ovarian lump.
  • The test for CA-125 may also be done on body fluids (other than blood) taken from the chest or stomach area.
  • High values of CA-125 in a woman who has been treated for ovarian cancer may mean that the cancer has returned. Often the high CA-125 level is found many months before the return of cancer can be found in another way.
  • Studies are being done to see if CA-125 can be used as a screening test for ovarian cancer. So far, there is not enough proof to show that this test works to find ovarian cancer early.


  1. Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.

Other Works Consulted

  • Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis: Saunders.

  • Fischbach FT, Dunning MB III, eds. (2009). Manual of Laboratory and Diagnostic Tests, 8th ed. Philadelphia: Lippincott Williams and Wilkins.

  • Pagana KD, Pagana TJ (2010). Mosby’s Manual of Diagnostic and Laboratory Tests, 4th ed. St. Louis: Mosby.

WebMD Medical Reference from Healthwise

Last Updated: May 29, 2013
This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.

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