The CA-125 Blood Test for Ovarian Cancer

Facts About the CA-125 Blood Test and TVUS

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The CA-125 blood test is a screening tool that measures the amount of a protein (CA-125) in the blood. Elevated levels can indicate ovarian cancer in some women, or indicate recurrence in women who have previously been diagnosed and treated for the disease. Many women with ovarian cancer will have high levels of CA-125 in their blood, making this test useful as a tumor marker to help guide treatment since a high level can often go down when treatment is working.

What is CA-125?

CA-125 (cancer antigen-125) is a protein found at elevated concentrations in ovarian cancer cells that are released into the bloodstream. A simple blood test can measure CA-125 levels in the blood. This test is also called a CA-125 tumor marker or biomarker test.

The CA-125 blood test is one of two tests used most often to screen for ovarian cancer. The other test is a transvaginal ultrasound (TVUS) that uses an ultrasound wand placed into the vagina to help find a possible mass (or tumor) in the ovaries. Unfortunately, it can't actually tell if a mass is cancerous or benign.

Why the CA-125 Test is Not Used as a Screening Tool for All Women

The problem with using the CA-125 test for screening is that other conditions can also cause high levels. 

Elevated CA-125 levels can be caused by a myriad of conditions, such as:

  • Menstruation
  • Certain cancer treatment drugs can also influence the test, producing a false positive.

Not all women who have ovarian cancer have elevated CA-125 levels, so a normal level does not mean that a woman does not have ovarian cancer. The test simply fails to detect 100 percent of true cases of ovarian cancer and misdiagnoses the disease because of the presence of common conditions, like the ones listed above.

Some studies have found that using the CA-125 and TVUS to screen women of average risk for ovarian cancer actually led to more testing and sometimes more surgeries, while the number of deaths caused by ovarian cancer failed to decrease. That is why major medical or professional organizations do not recommend the routine use of the CA-125 or TVUS tests to screen for ovarian cancer.

The door is not closed on the possibility of a CA-125 screening test for ovarian cancer, however. Several studies are underway to determine how the test could be used to screen at average risk women, much like a Pap smear. 

Who Should Get the CA-125 Test

Women who are at a high risk of developing ovarian cancer may benefit from regular CA-125 screening.

If you have a strong family risk of ovarian or breast cancer, it may be recommended that you have regular screenings. Some doctors may want to do a genetic test to see if you have a mutated BRCA1 or BRCA2 gene before making a recommendation about screening. When these genes are mutated, it can greatly increase the risk of ovarian cancer in women.

Some women who have been previously diagnosed and successfully treated opt to have regular CA-125 screenings. The effectiveness at detecting ovarian cancer early is still debated among some physicians, so not every doctor supports the test.

If you were previously treated for ovarian cancer and would like to be screened, talk to your doctor.

Opting Out of the CA-125 Screenings

You always have the choice to decline to have regular CA-125 screenings. Some women feel that regular screening cause too much stress and worry that interferes with their everyday lives. The decision to have regular screenings is personal and should be discussed with your doctor.

If you are currently being treated for ovarian cancer, your doctor may want to order regular CA-125 tests to gauge the protein levels throughout treatment. Decreasing levels can indicate that treatment is effective.

Prior to beginning treatment, your doctor may order a baseline CA-125, which he will use to compare future CA-125 test results.


The American Cancer Society. Can ovarian cancer be found early? Accessed Feb 10th, 2016.

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