What Is a CA-125 Blood Test?

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:

  • pregnancy
  • normal menstruation
  • endometrial and fallopian tube cancers
  • noncancerous growths in the uterus, such as uterine fibroids
  • endometriosis, which is a condition in which the cells of the uterus grow in other areas of the body, such as the ovaries and the bladder
  • pelvic inflammatory disease, which is a disorder in which the uterus, fallopian tubes, or ovaries become infected
  • cancer of the pancreas

A CA-125 blood test involves taking a small sample of blood, typically from a vein in the arm. The following will occur:

  • First, a healthcare provider will clean and disinfect the area with an antiseptic.
  • Then, they’ll wrap an elastic band around your upper arm so your veins swell with blood.
  • Once they find a vein, they’ll gently insert the needle into the vein. They’ll collect the blood in a small tube attached to the needle.
  • After enough blood has been drawn, they’ll remove the needle and cover the puncture site to stop any bleeding.
  • The blood sample will then be sent to a laboratory for analysis.
  • Once the laboratory has your results, your doctor will schedule an appointment to discuss them with you.

A CA-125 blood test is a low-risk procedure. The risks of the test are common to all blood tests and include:

  • difficulty obtaining a blood sample, which results in multiple needle sticks
  • excessive bleeding at the puncture site
  • fainting due to blood loss
  • infection at the puncture site

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

  • uterine fibroids
  • endometriosis
  • pelvic inflammatory disease
  • pregnancy
  • menstruation

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.