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  • Also Known As:
  • Cancer Antigen 125
  • CA-125 Tumor Marker
  • CA 125 Blood Test
  • CA125 Blood Test
  • Formal Name:
  • Cancer Antigen 125
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Test Quick Guide

Cancer antigen 125 (CA-125) is a protein that may be found at higher levels in people with certain types of cancer and other health conditions. The CA-125 test checks the levels of this protein in the blood.

The CA-125 test is a type of  tumor marker test. This test is used in the process of monitoring a patient’s response to ovarian cancer treatment, and detecting recurrence of ovarian cancer after treatment.

About the Test

Purpose of the test

The purpose of a CA-125 test is to measure the amount of CA-125 in the blood. Although CA-125 may be elevated in several health conditions and multiple types of cancer, testing for CA-125 is typically reserved for patients with suspected or confirmed ovarian cancer. A doctor may order a CA-125 test for several reasons:

  • Diagnosing a pelvic mass: CA-125 testing may be used to help determine if a pelvic mass seen on an imaging test could be related to ovarian cancer. Around 80% of patients with the most common type of ovarian cancer have elevated CA-125 levels.
  • Screening in high-risk patients: CA-125 testing is used to screen for ovarian cancer in patients at high risk of developing ovarian cancer due to hereditary cancer syndromes, such as those with inherited BRCA1 and BRCA2 gene mutations. CA-125 testing is not used to screen for ovarian cancer in patients who are not at a high risk of developing this disease.
  • Evaluating treatment response: Testing levels of CA-125 helps doctors monitor how well a patient’s ovarian cancer is responding to treatment.
  • Estimating prognosis: Although not all expert groups agree, some recommend measuring levels of CA-125 to help estimate a patient’s prognosis or chance of recovery from ovarian cancer.
  • Monitoring for cancer recurrence: Monitoring the level of CA-125 helps doctors check for signs of a return of cancer after a patient has completed treatment for ovarian cancer.

What does the test measure?

CA-125 testing measures the amount of the CA-125 protein found in the blood. CA-125 is measured in units per milliliter, or U/mL.

Both cancerous and noncancerous conditions may affect blood CA-125 levels. Many healthy cells produce low levels of CA-125, including cells of the ovaries, pancreas, breast, and lining of the chest and abdomen. Cancer and other health conditions that cause irritation or inflammation in these organs can increase CA-125 levels. Conditions that may cause an elevated CA-125 level in the blood include:

  • Ovarian cancer
  • Cancers of the pancreas, breast, and lung
  • Endometriosis
  • Uterine fibroids
  • Pregnancy
  • Menstruation
  • Liver disease

Finding a CA-125 Test

How to get tested

The CA-125 test is ordered by a doctor or other healthcare provider. The blood draw for this test may take place in a laboratory, clinic, doctor’s office, or hospital.

Can I take the test at home?

At this time, there is no at-home test currently available for CA-125 levels. The CA-125 test requires a blood draw in a clinical setting.

How much does the test cost?

The cost of a CA-125 test may depend on where you have the test performed and your health insurance coverage. The total cost of the test can include the office visit, the technician’s fees for obtaining the blood sample, and the laboratory’s fees for performing the test..

If your doctor has prescribed a CA-125 test for you, your insurance provider usually covers these fees and costs. Patients may be responsible for some out-of-pocket costs, such as  deductibles and copayments. Your doctor, insurance provider, and laboratory staff can give you more information about the cost of CA-125 testing.

Taking the CA-125 Test

The CA-125 test is performed on a sample of blood. To obtain the sample, a health professional uses a small needle to draw blood from a vein.

Before the test

You generally do not need to prepare in any specific way before CA-125 testing. To make sure the test is as accurate as possible, you should talk to your doctor if you are taking any prescription medications or over-the-counter drugs.

During the test

The blood sample for CA-125 testing is drawn from a vein, usually in your arm. The technician who draws your blood may begin by tying a rubber tourniquet around your upper arm in order to increase pressure in the vein. The technician will then use an antiseptic wipe to clean the site before inserting a thin needle into your vein and collect a small amount of blood.

You may feel a slight pain or stinging when the needle is inserted or removed, but this is usually mild and does not last long. The entire procedure usually takes no more than five minutes.

After the test

After your blood is drawn, the technician will apply a small bandage to stop any bleeding. You may need to keep this in place for an hour or more.

Generally, you can return to normal activities after having this test. Rarely, people who have their blood drawn may feel lightheaded, continue to bleed, or develop an infection where the blood was taken. Contact your doctor if you notice any of these symptoms.

CA-125 Test Results

Receiving test results

You will usually get the results of your test a few business days after the laboratory receives your blood sample. Your doctor may contact you or schedule an appointment to go over the results and discuss what they mean. Your test report may also be sent to you by email or postal mail, or it may be made available online.

Interpreting test results

Levels of CA-125 can vary from patient to patient, so a doctor must take a patient’s unique situation into account when interpreting CA-125 test results. Your doctor is in the best position to put your test results into context and explain what they could mean for your health.

In patients being evaluated for a pelvic mass, an abnormal CA-125 test can be one indication that the mass may be related to ovarian cancer. The test is more informative in patients who have gone through menopause.

For screening patients at high risk of developing ovarian cancer, an elevated level of CA-125 is not enough to diagnose cancer on its own. The CA-125 level is considered alongside other tests to confirm or rule out cancer, such as further blood tests, imaging tests, and biopsies.

If you are undergoing ovarian cancer treatment, your doctors will compare your pre-treatment level of CA-125 with subsequent test results. If CA-125 levels go down after an elevated result prior to treatment, this may indicate that cancer treatment is effective. If the levels increase or do not change, the treatment may not be effective.

If you have completed treatment for ovarian cancer, you may receive follow-up CA-125 testing periodically. An abnormal CA-125 test result can be an early sign that the cancer has returned.

Individual laboratories may use different methods to test CA-125. If CA-125 is being monitored over time, it’s helpful to use the same laboratory to process each test. Results obtained from different laboratories may not be directly comparable.

View Sources


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National Cancer Institute. Ovarian epithelial, fallopian tube, and primary peritoneal cancer treatment (PDQ®)–Health professional version. Updated May 20, 2021. Accessed May 25, 2021. https://www.cancer.gov/types/ovarian/hp/ovarian-epithelial-treatment-pdq

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U.S. Preventive Services Task Force. Ovarian cancer: screening. Updated February 13, 2018. Accessed May 25, 2021. https://www.uspreventiveservicestaskforce.org/uspstf/recommendation/ovarian-cancer-screening

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