What is a carcinoembryonic antigen test (CEA)?
A carcinoembryonic antigen (CEA) test is a blood test used to help diagnose and manage certain types of cancers. The CEA test is used especially for cancers of the large intestine and rectum. Your doctor can also use the test results to help determine if a cancer treatment is working.
An antigen is a substance that’s made by cancerous tumor cells. Sometimes antigens are released into the bloodstream. 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 the cancer is not gone. It may also mean that the cancer has spread to other parts of your body.
Smoking can increase the amount of CEA in your body even in the absence of cancer. You should tell your doctor if you smoke.
The CEA test has different uses. Your doctor can order a CEA test if your symptoms suggest you might have cancer. A CEA test can help your doctor find out if a cancer treatment is working. These treatments may have included surgery, chemotherapy, radiation, or a combination of all three. Your doctor might also use the CEA test to help determine if a cancer has come back, or recurred, after finishing treatment.
A CEA test is most useful after a diagnosis of 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’s usually not used to screen or diagnose you if you’re healthy or aren’t showing any symptoms of a disease. But if someone has a familial genetic syndrome for colon cancer then it’s reasonable use CEA as a screening tool. These cases are rare.
Your doctor may begin monitoring levels of CEA before you begin treatment if you’re diagnosed with cancer. This will establish a baseline level for your CEA. A single CEA value is usually not as informative as many values and the trends of these values over time. Your doctor will perform the test repeatedly before, during, and after treatment to check for changes.
The CEA test is a blood test performed in your doctor’s office. Blood is usually drawn from a vein in your arm. The blood draw process, or venipuncture, usually involves the following steps:
- A healthcare provider will clean the puncture site 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 is then inserted into your vein to collect blood into an attached vial or tube.
- The band is unwrapped from your arm.
- A laboratory will analyze your blood sample.
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. If you have values that are that high, it doesn’t mean you have cancer. Other reasons can cause levels higher than 3 ng/mL. These can include:
- chronic smoking
- inflammatory bowel disease (IBD)
Levels of CEA higher than 20 ng/mL are considered very high. If you have CEA levels this high and you also have symptoms of cancer, it strongly suggests the 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 shouldn’t 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 symptoms. You and your doctor can work together to decide your best treatment option if your doctor determines you have cancer.