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Cancer antigen 125 (CA-125) is a protein found in ovarian cancer cells. A CA-125 blood test measures the amount of cancer antigen 125 in the bloodstream. The protein is produced by the cells and can be found in the blood.
A CA-125 blood test may be used to monitor ovarian cancer during and after treatment. In some cases, it might be used to check for early signs of ovarian cancer in women who are at a high risk for the disease. However, a CA-125 blood test isn’t accurate enough to screen for ovarian cancer in all women because many different conditions can cause abnormal CA-125 levels.
A CA-125 blood test is often ordered to monitor the progression of ovarian cancer. Baseline CA-125 levels are measured before someone undergoes treatment for ovarian cancer. A drop in CA-125 levels during and after treatment usually indicates that treatment has been successful. Increases in CA-125 levels following treatment may signify a recurrence of the disease.
After treatment for ovarian cancer, the CA-125 blood test is used for several years to ensure the disease was treated successfully. It’s typically ordered every two to four months for the first two years following the completion of cancer treatment. After this period, the test is ordered every six months for three years and then once per year.
Some doctors may recommend the CA-125 blood test to women with a strong family history of ovarian cancer. However, the test usually isn’t used to screen for ovarian cancer in women who have an average risk of developing the disease. There are numerous disorders and conditions that can cause elevated CA-125 levels, such as:
A CA-125 blood test involves taking a small sample of blood, typically from a vein in the arm. The following will occur:
A CA-125 blood test is a low-risk procedure. The risks of the test are common to all blood tests and include:
CA-125 blood test results can vary depending on the laboratory that performed the analysis. In most instances, however, CA-125 levels are considered elevated if they are above 35 units per milliliter.
High levels of CA-125 don’t necessarily confirm the presence of ovarian cancer or any other type of cancer. CA-125 levels may be elevated due to another health condition, such as
Certain cancer medications and surgeries can also alter CA-125 levels. You should discuss your specific results with your doctor to determine if additional testing is required.
When the CA-125 blood test is being used to monitor the effectiveness of treatment for ovarian cancer, high levels of CA-125 often indicate that the cancer isn’t responding to treatment. If this occurs, you may need to have alternative treatments to combat the disease. A decline in CA-125 levels during treatment indicates that the cancer is responding to treatment.
Some women with ovarian cancer have normal baseline levels of CA-125, which means they have tumors that aren’t producing the CA-125 protein. If this happens, a CA-125 blood test won’t help your doctor monitor the progression of ovarian cancer.
Written by: Darla Burke
Medically reviewed on: Feb 16, 2016: George Krucik, MD MBA
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