CA 125 Blood Test: What Is It, Uses & Normal Levels

Updated in January 2024

CA 125 is a protein that is naturally produced by the ovaries, uterine lining, fallopian tubes and intestines. Levels may become increased due to pregnancy, a period, endometriosis and, sometimes, in cases of cancer, especially ovarian cancer.

Normally, a CA 125 blood test is ordered when ovarian cancer is suspected. It can also be ordered to monitor the response of ovarian cancer to treatment, or to identify the return of another tumor following surgery.

It is important to emphasize that this exam should not be carried out without close medical monitoring. High CA-125 levels should be assessed by the ordering physician, so that further tests can be completed, like an ultrasound, MRI or biopsy.

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What is it used for

The CA 125 blood test is used for:

  • Assist in the diagnosis of ovarian cancer
  • Monitor the response to chemotherapy in cases of ovarian cancer;
  • Confirm that ovarian cancer cells has been completely removed after surgery
  • Identify whether ovarian cancer has returned after treatment with surgery

The CA 125 blood test may also be indicated to monitor the evolution of some membranal tumors.

How it is tested

The CA 125 blood test is carried out by analyzing a blood sample that is collected in a health care setting. The CA 125 blood test is normally ordered by your doctor if ovarian cancer is suspected, or to monitor cancer treatment. Check out other blood tests for cancer that your doctor may consider.

Generally, fasting is not necessary to perform the test and the result can be obtained after one day depending on the lab.

Normal CA 125 levels

The CA 125 level is considered to be normal if it is under 35 U/mL. However, the reference ranges may vary slightly from lab to lab, and depending on the method performed. Therefore, it is important to refer to the normal reference ranges indicated in the lab report.

High CA 125 levels

CA 125 is considered to be high when levels are over 35 U/mL. This can occur for the following reasons:

  • Menstruation
  • Pregnancy
  • Coffee intake
  • Endometriosis
  • Tuberculosis
  • Pelvic inflammatory disease
  • History of hysterectomy
  • Cirrhosis
  • Uterine fibroid
  • Ovary cancer
  • Other membranal tumors

Other types of tumors (from breast, endometrial, lung and pancreatic cancers, for example) can also cause high CA 125 levels. Therefore, further testing through MRI and biopsy are usually ordered to confirm a , and it is important to carry out other tests, such as MRI and biopsy to confirm the diagnosis.

Also recommended: 12 Potential Signs of Cancer (& What To Do)

When is CA 125 considered cancer?

There is no specific value of CA 125 that is considered to be a direct indicator of cancer. However, the risk for cancer is greater when it is above 35 U/mL, especially in women who have other possible symptoms of cancer and other tests that may indicate cancer.

The CA 125 measurement alone does not confirm the diagnosis of ovarian cancer. Additional tests are required, such as transvaginal ultrasound and MRI.