CA-125 Blood Test

Written by Darla Burke | Published on May 30, 2012
Medically Reviewed by Brenda B. Spriggs, MD, MPH, FACP

What is A CA-125 Blood Test?

Cancer antigen 125 (or “CA-125”) is a protein found in ovarian cancer cells. The protein is produced by the cells and is also found in the blood.

The CA-125 blood test is used to measure the amount of CA-125 protein in the bloodstream. Measurement of the protein using the CA-125 test is used to track response to treatment for ovarian cancer. It is not used to screen for ovarian cancer because it can appear in high levels during pregnancy, pelvic infections, or during normal menstruation.

High levels of this protein can also be seen in other disorders of the female reproductive system such as infections and noncancerous and cancerous growths.

Why is the Test Ordered?

The CA-125 test is often ordered to monitor the progression of ovarian cancer. Baseline CA-125 levels are measured before a patient undergoes treatment for ovarian cancer. A drop in CA-125 levels during and following treatment indicates that treatment has been successful. Increases in CA-125 levels following treatment may indicate a recurrence of the disease.

Following treatment for ovarian cancer, the CA-125 test is used for several years to ensure treatment success. In particular, a CA-125 test is typically ordered every two to four months for the first two years following the completion of cancer treatment. After this time period, the test is ordered every six months for three years and then annually.

It is important to stress again that the CA-125 test should not be ordered as a screening test for ovarian cancer because there are other disorders that can have elevated levels such as:

  • uterine fibroids or noncancerous growths in the uterus
  • endometriosis, a condition where cells of the uterus grow in other areas of the body such as the ovaries, bowel, and bladder
  • pelvic inflammatory disease (PID), a disorder involving inflammation of the uterus, fallopian tubes, or ovaries
  • endometrial and fallopian tube cancers

According to the Mayo Clinic, the CA-125 test is not recommended for women who have only an average risk for ovarian cancer. Women who have a high risk for ovarian cancer, for instance, those who have had positive testing for breast cancer genes like BRCA1 and BRCA2, may choose to have periodic CA-125 testing performed (Mayo Clinic, 2011).

How is the Test Administered?

The CA-125 test is typically administered by a healthcare professional in a clinical setting. Patients must provide a blood sample. This sample is commonly extracted from the arm through a needle. The blood is collected in a tube and sent to a laboratory for analysis. Once the results have been reported by the lab your physician will be able to discuss them with you.

What are the Risks of the Test?

The CA-125 test is a blood test that carries with it minimal risks for the patient. The risks of the test are common to all blood tests and include:

  • difficulty obtaining a sample, resulting in multiple needle sticks
  • excessive bleeding at the needle site
  • fainting as a result of blood loss
  • the accumulation of blood under the skin, known as a hematoma
  • development of infection where the skin is broken by the needle

Interpreting Your Test Results

Results from the CA-125 test will vary based on the laboratory completing the analysis. In most instances, CA-125 levels are considered elevated if they are above 35 U/mL.

Elevated levels of CA-125 do not necessarily confirm the presence of ovarian cancer or any other type of cancer. CA-125 levels may be elevated due to a number of reproductive health issues. Patients must discuss the results with their healthcare provider to determine if additional testing is required.

Physicians treating a patient with ovarian cancer can use the CA-125 test to help determine if treatment is effective. If CA-125 levels remain unchanged or increase during treatment, this indicates that the cancer is not responding to treatment. Physicians may need to consider alternative treatment to combat the disease. A decline in CA-125 levels during treatment indicates that the cancer is responding to treatment.

Some women diagnosed with ovarian cancer have normal baseline levels of CA-125. These patients typically have tumors that are not producing the CA-125 protein. In these cases, CA-125 will not help to monitor the progression of cancer. According to the Mayo Clinic, although CA-125 monitoring can be a useful addition to evaluating treatment of ovarian cancer, doing so hasn’t been shown to improve the treatment outcome. It is only one of several ways your physician will evaluate the effectiveness of your treatment (Mayo Clinic, 2011).

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