A carcinoembryonic antigen (CEA) test is a blood test used to help diagnose and manage certain types of cancers, especially cancers of the large intestine and rectum. This test can also be used to help determine if a cancer treatment is working.
An antigen is a harmful substance that’s released by a cancerous tumor. The CEA test measures the amount of CEA in the blood. A high amount of CEA in your body after a cancer treatment or surgery suggests that the cancer has not gone away. It may also mean that the cancer has spread to other parts of your body.
Smoking increases the amount of CEA in your body. You should tell your doctor if you smoke.
The CEA test can be used for different reasons. Your doctor can order a CEA test if your symptoms suggest that you might have cancer. A CEA test can help your doctor find out if a cancer treatment, such as surgery, chemotherapy, radiation, or a combination of all three, is working. Your doctor might also use the CEA test to help determine if a cancer has come back, or recurred, after treatment is finished.
A CEA test is most useful if you’ve been diagnosed with a type of cancer that’s known to produce CEA. Not all cancers produce CEA. Increased levels of CEA may be found in the following cancers:
- colorectal or colon cancer
- medullary thyroid carcinoma
- breast cancer
- cancer of the gastrointestinal tract
- liver cancer
- lung cancer
- ovarian cancer
- pancreatic cancer
- prostate cancer
The CEA test isn’t useful for diagnosing or screening the general population for cancer. It shouldn’t be used to screen or diagnose you if you’re healthy, you aren’t showing any symptoms of a disease, or you have a high risk of cancer.
Your doctor may begin monitoring levels of CEA before you begin treatment if you’re diagnosed with cancer. This is to establish a baseline level for your CEA. A single CEA value is usually not as informative as many values over a period of time. Your doctor will perform the test repeatedly before, during, and after treatment to assess changes over time.
The CEA test is a blood test performed in your doctor’s office. Blood will usually be drawn from a vein in 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 your upper arm to help make your vein fill up with blood.
- A needle will be gently inserted into your vein to collect blood into an attached vial or tube.
- The band is unwrapped from your arm.
- Your blood sample is sent to a laboratory for analysis.
As with any blood test, there’s a risk of bleeding, bruising, or infection at the puncture site. Moderate pain or a sharp pricking 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.
CEA levels will generally return to normal between one and four months after the cancer has been successfully removed.
Elevated levels of CEA occur when the CEA is higher than 3 ng/mL. These levels are considered abnormal. People with many types of cancers can have levels that are higher than 3 ng/mL. However, if you have values that are that high, it don’t necessarily mean you have cancer. Levels higher than 3 ng/mL can be found for reasons other than cancer, such as:
- cirrhosis of the liver
- chronic smoking
- inflammatory bowel disease
Levels of CEA higher than 20 ng/mL are considered very high. If you have CEA levels that are this high and you also have symptoms of cancer, it strongly suggests that cancer has not been removed successfully after treatment. It may also suggest that the cancer has metastasized, or spread, to other parts of your body.
Smoking may affect your CEA test results if you’re otherwise healthy. CEA is usually elevated but less than 5 ng/mL in people who smoke.
CEA levels should not be the only test used to determine if you have cancer. Your doctor will use the CEA test along with other tests and an evaluation of your overall symptoms. You and your doctor can work together to decide what your best treatment is if your doctor determines that you do have cancer.