A carcinoembryonic antigen (CEA) test is a blood test used to help diagnose and manage certain types of cancers, especially cancer of the colon. The test measures the amount of CEA present in the blood. If you already have cancer, this test helps a doctor determine if the treatment for the cancer is working.
An antigen is a harmful substance that is released by cancerous tumors. If you are receiving treatment or have had surgery for a previously diagnosed cancer, a higher amount of CEA in your body suggests that the cancer has not gone away. It may also mean that cancer has spread to other parts of the body. Smoking increases the amount of CEA in your body. You should tell your doctor if you smoke.
A doctor might order a CEA test for the following reasons:
- to help diagnose cancer in someone whose symptoms suggest that cancer is a possibility
- to find out if the treatment a patient is receiving for their cancer is working. The treatment might include surgery, chemotherapy, or radiation, or a combination of all three
- to find out if a cancer has come back (recurred) later on
A CEA test is most useful to monitor patients who already have been diagnosed with a type of cancer that is known to produce CEA. Not all cancers produce CEA. Increased levels of CEA may be found in the following cancers:
- colorectal (colon) cancer
- medullary thyroid carcinoma
- breast cancer
- cancer of the gastrointestinal tract
- liver cancer
- lung cancer
- ovarian cancer
- pancreatic cancer
- prostate cancers
Importantly, the CEA test is not useful in diagnosing or screening the general population for cancers. It should not be used to screen or diagnose healthy asymptomatic people, even people at high risk of cancer.
If you are diagnosed with cancer, your doctor may begin monitoring levels of CEA before you begin treatment to establish a baseline amount. A single CEA value is usually not as informative as gathering many values over a period of time. Your doctor will perform the test repeatedly before, during, and after treatment to assess changes over time.
According to the Mayo Clinic, CEA levels will generally return to normal amounts between one and four months after the cancer has been successfully removed. (Mayo Clinic)
The CEA test is a blood test performed by a healthcare practitioner at your doctor’s office. Blood will be drawn from a vein, usually on your arm. The blood draw process, or venipuncture, usually involves the following steps:
- The puncture site is cleaned with an antiseptic. The site is usually in the middle of your arm, on the opposite side of the elbow.
- A healthcare provider will wrap an elastic band around the upper arm to help make the vein fill up with blood.
- A needle will be gently inserted into the vein to collect blood into an attached vial or tube.
- The band is unwrapped from your arm.
- The blood sample is sent to a laboratory for analysis.
As with any blood test, there is a risk of bleeding, bruising or infection at the puncture site. Moderate pain or a sharp prick sensation may be felt when the needle is inserted.
A normal level of CEA is less than or equal to 3 nanograms per milliliter (ng/mL). Most healthy people have levels below this amount.
If the cancerous tissue has been successfully removed, CEA levels should return to this normal amount after about six weeks.
Elevated levels of CEA (higher than 3 ng/mL) are considered abnormal. The levels are higher than 3 ng/mL in many types of cancers, but that in itself does necessarily mean you have cancer. Higher levels can be found in non-cancerous disorders such as infections, cirrhosis of the liver, smoking, and inflammatory bowel disease.
Very high levels of CEA (higher than 20 ng/mL) in patients who also have symptoms of cancer strongly suggest that cancer has not been removed successfully even after treatment. It may also suggest that the cancer has metastasized (spread to other parts of the body).
Smoking may affect the test results in otherwise healthy people. Usually CEA is elevated, but still less than 5 ng/mL, in people who smoke.
CEA levels should not be the only test used to determine the presence or absence of cancer. A doctor will use the CEA in conjunction with other tests and an evaluation of the patient’s overall symptoms. If your doctor determines that you have cancer, he or she will decide on the best treatment.