The short answer
CEA (carcinoembryonic antigen) is a tumor marker measured in blood. It is used to follow certain cancers over time and check response to treatment. MedlinePlus says it is not used to screen for or diagnose cancer. Non-cancer causes and smoking can also raise it, so trends matter more than one value.
CEA is a tumor marker measured with a blood test.
MedlinePlus says CEA tests are not used to screen for or diagnose cancer.
Non-cancer causes, including smoking and some conditions, can raise CEA. Some people with cancer have a normal CEA.
The trend across tests usually matters more than a single value.
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The short version
CEA stands for carcinoembryonic antigen. It is a tumor marker: a substance measured in blood that can run higher in some cancers. This page explains what a CEA result can and cannot tell you. But a tumor marker is not a simple cancer test. CEA is used mainly to follow certain cancers over time. It is not used to screen for cancer or to diagnose it.
What CEA is used for
CEA is most often used to monitor cancers such as colorectal cancer. NCI lists colorectal cancer and some other cancers. MedlinePlus says care teams may check it to:
- Learn how advanced a cancer is before treatment.
- Check whether treatment is working.
- Look for a return of cancer after treatment.
Notice that all of these uses assume the situation is already known and being followed. CEA is a tracking tool more than a screening or diagnostic one.
Why it is not used alone
Several non-cancer factors can raise CEA. Smoking is one, and you may be asked to stop for a while before the test. MedlinePlus also lists COPD (chronic obstructive pulmonary disease), diabetes, liver disease such as cirrhosis, stomach ulcers and gastritis, and inflammatory conditions such as Crohn's disease and diverticulitis. People with cancer can also have a normal result, and many non-cancer conditions raise CEA. So a single value is easy to misread on its own. Care teams read it together with imaging, exams, and other results.
The trend matters most
As with many markers, the pattern across several tests says more than any one reading. NCI notes that repeated measurements during treatment can show whether a tumor is responding. Ask your care team how to read your trend, since non-cancer causes can also change the number.
What to ask
Ask why your care team is measuring CEA. Ask what your level and its trend suggest. Ask whether a non-cancer cause could explain a change, and how the result fits with your imaging. Their reading of your full picture is what applies to you.
Sources
Common questions
Does a high CEA mean I have cancer?
Not by itself. CEA can be raised by non-cancer causes, including smoking and certain conditions such as COPD, diabetes, liver disease and inflammatory bowel conditions. MedlinePlus says CEA tests are not used to screen for or diagnose cancer. Your care team interprets it in context.
What is CEA used for?
CEA is most often used to follow certain cancers, such as colorectal cancer, over time — for example, to judge how advanced a cancer is before treatment, check whether treatment is working, or look for a return after treatment. It is one tool among several, not a stand-alone test.
Why does my CEA go up and down?
CEA can shift for many reasons, including smoking and non-cancer conditions. NCI says repeated measurements during treatment can show whether a tumor is responding, so care teams look at the pattern across tests. Ask your care team what a change in trend means for you.
Can smoking affect CEA?
Yes. Smoking can raise CEA levels, which is one reason the test is not used on its own to diagnose cancer. Your care team accounts for factors like this when interpreting your result.
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Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes, and this is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Editorial review complete — This page completed Cancer Explained's editorial checks (sources, safety, plain language, duplication). It has not been reviewed by a physician or other healthcare professional.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
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