A CA-125 blood test can be used as part of an overall approach to monitoring ovarian and other cancers. It’s used as a screening tool for people at very high risk for ovarian cancer.
A CA-125 test is a blood test that measures the amount of the protein CA-125, also called cancer antigen 125, in your body.
CA-125 is a type of biomarker or a substance in your blood that may be a sign of a condition or disease. A high level of CA-125 can be a sign of ovarian cancer. Your ovaries are a pair of reproductive glands that store and release eggs and produce hormones.
A CA-125 test can have both false positive and false negative findings. CA-125 levels can be normal even if you have cancer (false negative), or they can be elevated when you don’t have cancer (false positive). For this reason, a CA-125 test isn’t an effective screening for ovarian cancer.
Instead, healthcare providers will order a CA-125 blood test as part of an overall approach to monitoring certain types of cancer, especially during and after cancer treatment.
Providers also use this test for the early detection of ovarian cancer in people who are at high risk. This could include factors such as if an immediate family member had ovarian cancer or if you have been found to have a genetic mutation or error that increases your risk of developing ovarian cancer. A CA-125 test isn’t useful for people with no symptoms or risk factors.
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It doesn’t detect cancer. The CA-125 test is used during the diagnosis, treatment and monitoring of ovarian cancer in certain people. It’s also used for cancer in your fallopian tubes or peritoneum.
A CA-125 blood test may be used to:
If your healthcare provider thinks you may have ovarian cancer or is currently treating you for ovarian cancer, a CA-125 test may be used to monitor your condition.
You may need a CA-125 test if you’re at increased risk for ovarian cancer. Some factors that put you at increased risk are:
The test involves taking a small sample of your blood for testing. You may feel a small prick or sting when the needle is placed in your arm. The blood draw should take a few minutes. There are no dietary restrictions before the test.
You don’t need to do anything to prepare for a CA-125 test.
There is little risk involved with having your blood taken. Taking a blood sample from some people may be more difficult than others. In rare cases, infection or excessive bleeding occurs. More commonly, people feel lightheaded during blood draw or bruise at the puncture site afterward.
Many things other than ovarian cancer can lead to a “positive” test score. Some other conditions that can increase CA-125 levels in your blood are:
Because high levels of CA-125 can show up in other conditions, a CA-125 test is only used in conjunction with other diagnostic tools.
Your results should be interpreted by your healthcare provider. Acceptable ranges may vary, and different labs may use different tests. Generally, levels higher than 35 units per milliliter are considered irregular. However, high levels don’t mean you have cancer or that cancer has returned. Discuss your results with your provider to determine what it means and if additional testing is needed.
Your healthcare provider will discuss what your test results mean for you. Even if the test shows high CA-125 levels, further testing is needed to diagnose cancer. The result of one test alone isn’t usually helpful. Your provider will order CA-125 tests in a series so they can identify changes in levels.
If you have ovarian cancer, a high CA-125 reading may mean cancer has returned or progressed. A lower score may indicate treatment is working.
Your CA-125 levels don't correlate with how much cancer is in your body. More testing is needed to confirm the extent of your condition.
If your healthcare provider orders a CA-125 test and the results are positive, they’ll likely order additional tests to learn more. These could include transvaginal ultrasound or magnetic resonance imaging (MRI). They may also decide to repeat the CA-125 test later to see if the results change.
A note from Cleveland Clinic
A CA-125 test is just one tool healthcare providers use to measure if cancer treatment is working. It's also used to screen for cancer in people who are high risk. It shouldn’t be used for people who have no symptoms or risk factors for ovarian cancer. Talk to your provider about your concerns with the CA-125 test and what the results mean for your care. Only your healthcare provider should interpret your test results.
Last reviewed by a Cleveland Clinic medical professional on 07/12/2022.
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