Carcinoembryonic antigen (CEA) is a tumor marker found in the blood or in other bodily fluids that can be used to monitor treatment for certain cancers.

This article explains what the CEA test is, when it can be helpful in cancer treatment, and how to interpret its results.

Purpose of the Test

CEA is a type of tumor marker used to monitor cancer. Tumor markers are substances that are either made by cancer or made by the body in response to cancer.

Carcinoembryonic antigen (CEA) is a protein that is made by a fetus during pregnancy, then drops to very low levels under normal conditions shortly after birth. Since it is produced in large amounts by some tumors, it can be used to monitor cancer treatment.

CEA levels may be high in connection with a number of conditions. As a result, this test cannot establish a cancer diagnosis on its own and is not used as a general screening tool for cancer.

Instead, healthcare providers will look at CEA levels over time, along with imaging studies and other tests, to help plan and monitor cancer treatment. When levels of CEA decrease, it may indicate that a cancer is responding to treatment. When CEA levels increase, it may suggest a recurrence, progression, or spread (metastasis) of the cancer.

Meaning of Carcinoembryonic Antigen (CEA)

CEA is a protein produced by normal cells that is overexpressed, or produced in much higher amounts, in some cancers known as adenocarcinomas. CEA may be found in blood, urine, stool, and other bodily fluids, as well as in a tumor itself. It is more likely to be produced by slow-growing, well-differentiated tumors (tumors made up of cancer cells that appear very similar to normal cells) than by poorly differentiated tumors.

The name “carcinoembryonic” refers to common sources of the CEA protein, with “carcino-” representing the tumor and “embryonic” referring to the fact that high levels of CEA are present in a fetus during development.

Uses/Indications

Your healthcare provider may test CEA levels in a number of circumstances, including the following.

  • To monitor cancer treatment: Monitoring serial CEA levels can help track the effectiveness of treatment. If CEA levels are decreasing, it usually means a tumor is responding to treatment. If levels are increasing, it may mean the tumor is progressing. CEA is often ordered as a baseline test at the beginning of cancer treatment for this reason.
  • To monitor for recurrence of cancer: If CEA levels were normal and are increasing, it may mean that a tumor has recurred. A major use of the test is to detect relapse after curative treatment for colon cancer.
  • Cancer staging: Smaller tumors may have lower CEA levels, whereas larger tumors may have higher levels (greater tumor burden). Understanding the stage of cancer is important in selecting the most appropriate treatments. A 2018 study found that CEA correlated well with the stage (at least stage I to III) of colon cancer.
  • To see if cancer has spread to certain areas: Spread (metastasis) to some regions of the body may cause much higher elevations of CEA. For example, metastasis to the pleural cavity (with a malignant pleural effusion), peritoneal cavity (within the abdomen), or the central nervous system often leads to very high CEA levels.
  • To estimate prognosis: Elevated levels of CEA after colon cancer surgery may indicate a poorer prognosis. CEA can also help estimate prognosis with non-small cell lung cancer and breast cancer.
  • As an adjunct (additional test) in diagnosis: While CEA levels cannot diagnose cancer, they are one puzzle piece that can help establish a diagnosis.
  • As a screening test for certain people: CEA levels are not considered useful diagnostic tools in the general population, but this test may be ordered to screen for cancer in people with some hereditary colorectal cancer syndromes.
  • In medical studies: A 2019 review of 19 studies notes that CEA may be a reasonable endpoint (a sign that a treatment is effective) in clinical trials looking for better treatments for metastatic colon cancer. In this meta-analysis, CEA response was strongly linked with overall survival.

Cancers Monitored With CEA

CEA is most commonly used with digestive tract cancers. It may also be used as a tumor marker test to monitor a number of different cancer types, including:

  • Colorectal cancerPancreatic cancerStomach cancer (gastric cancer)Lung cancerBreast cancerOvarian cancerThyroid (medullary) cancerBladder cancerHead and neck cancerCervical cancerKidney cancerProstate cancerLymphomaMelanoma

Limitations

One significant limitation of the CEA test is that it is not increased in all cancers, and is not as likely to be present in a cancer’s early stages. This is one reason why it’s not an effective screening test. For example, It is present in roughly 70 percent to 80 percent of advanced colon cancers, but only in around 25 percent of early-stage colon tumors.

False Positives

There are also many benign (noncancerous) and inflammatory conditions that can increase CEA, leading to false positive results.

Benign conditions associated with an increase in CEA levels include:

  • SmokingCOPDPancreatitisInflammatory bowel diseases such as Crohn’s disease or ulcerative colitisHepatitisCirrhosis of the liverPeptic ulcer diseaseGallbladder inflammation (cholecystitis)Lung infectionsHypothyroidismColon polypsBenign breast disease

Another limitation is that CEA levels may not reflect what is happening with a tumor at the time of the test. For example, CEA levels may be very high during and after chemotherapy.

Similar Tests

There are a number of other tumor markers that can be used to monitor cancer treatment, though the particular markers that are tested vary with the type of cancer being followed. For example:

As cancer cells die, CEA is released into the bloodstream. Levels can remain elevated for a few weeks after treatment, even if a tumor is responding well.

  • Cancer antigen 15.3 (CA-15.3) may be used to monitor breast cancer, lung cancer, ovarian cancer, uterine cancer, bladder cancer, and more.
  • Cancer antigen 19.9 (CA 19.9) may be used to monitor colorectal cancer, pancreatic cancer, liver cancer, and more.
  • Cancer antigen 27.29 (CA 27.29) may be used to monitor for breast cancer recurrence or progression and in stomach cancer, colon cancer, lung cancer, and more.
  • Prostate-specific antigen (PSA) is used only to monitor (and screen for) prostate cancer.

Complementary Tests

Risks/Contraindications

There is very little risk in doing a CEA test, since it is a simple blood test. Uncommon side effects include bleeding, bruising (hematomas), lightheadedness, or fainting during the blood draw, as well as, rarely, infection.

CEA levels are not used alone to monitor cancer, but rather are used along with symptoms, physical findings, other tumor markers or biomarkers, and imaging studies (such as a CT scan) to evaluate cancer and plan treatment.

The Test

The CEA test may be done in the hospital or in a clinic. The test is often run on a blood sample, but may also be run on fluid obtained from the central nervous system (via a lumbar puncture or spinal tap), from the pleural cavity (via thoracentesis), or from the peritoneal cavity (via paracentesis). The description below refers to having the test done in the most common way: through a blood test.

Before the Test

There are no diet or activity restrictions prior to having the CEA test. You will usually be required to have your insurance card.

During the Test

A lab technician will cleanse the area over the vein to be used (usually an arm vein) with antiseptic, then apply a tourniquet. You may feel a sharp sting as the needle is introduced into the vein, then some slight pressure.

After the sample is obtained, the needle is removed and a bandage is placed over the puncture site. Some people may feel lightheaded or faint when having their blood drawn. Let the technician know if you have had any problems in the past or if you feel “funny” during the blood draw.

After the Test

The sample will be sent to the laboratory for analysis. Possible side effects after the test are very uncommon, but may include:

  • Bleeding (persistent bleeding at the puncture site is most common for people who are on blood thinners, have a blood disorder, or are on chemotherapy)Bruising (a hematoma or large bruise may form in some cases)Infection (the risk of infection is very low, but higher in people who are on chemotherapy or otherwise immunosuppressed)

Interpreting Results

A single CEA test may give doctors some idea about what is happening in your body. The test should be repeated if it is abnormal to verify the result.

Reference Range

The levels of CEA that are considered “normal” may vary somewhat between different labs. In general, a normal CEA in an adult is as follows:

CEA levels are most helpful when repeated over time to observe how they change. As a result, “serial testing” gives more information than a single test.

  • Less than or equal to 2.5 ng/ml (0-2.5) in nonsmokersLess than or equal to 5.0 ng/ml (0-5.0) in people who smoke

High CEA

There are a number of both benign and cancerous conditions that may cause an elevated CEA level.

Certainly, there are many exceptions to this general rule. For example, a CEA over 20.0 may be due to an early-stage cancer plus a benign condition, such as hypothyroidism in a person who smokes.

Causes of a High CEA Level

  • A CEA over 2.5 (or 5.0 in smokers) can mean either cancer or benign inflammatory conditions (or both).
  • A CEA over 10.0 ng/ml often means cancer.
  • A CEA over 20.0 ng/ml often means cancer that has metastasized.
  • Very high levels (sometimes well over 100 ng/ml) are frequently seen with metastases to the pleural cavity, peritoneal cavity, and central nervous system.

Follow-Up

As noted, CEA is often most useful when repeated over time. The amount of time between tests, however, can vary based on many factors.

For example, when surgery is done with curative intent for people with stage II or stage III colon cancer, a CEA is usually recommended every three months for at least three years after surgery. With treatment of metastatic colon cancer, in contrast, the test is often done every one month to three months.

Summary

A CEA test may be useful in monitoring cancer treatment, but it’s important to note that it should not be used alone as it is a lot less reliable than monitoring through imaging exams, for example. It is most helpful when it is monitored longitudinally over time rather than as a single value at a single time point.

Since CEA levels can take some time to decrease during colon cancer treatment, a healthcare provider will consider the whole picture rather than make treatment decisions based on CEA levels alone.

A Word From Verywell

CEA levels can help your healthcare providers monitor cancer treatment and predict prognosis. However, the prognosis of many cancers is changing with newer treatments and technology. Keep in mind that currently available statistics don’t necessarily reflect those improvements.