What Is the Carcinoembryonic Antigen (CEA) Blood Test?

What to expect when undergoing this test

Technician holding blood sample for checking CEA in a patient with cancer
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Carcinoembryonic antigen (CEA) is a tumor marker in the blood or other bodily fluids that can be used to monitor certain cancers such as colorectal cancer. When levels are decreasing, it may indicate that cancer is responding to treatment, and when increasing, may suggest a recurrence, progression, or spread (metastasis) of the disease. When used along with imaging studies and other tests, it can be helpful in planning and monitoring treatment. The test has limitations in that not all cancers (especially early stage cancers) have elevated levels, and false positives may occur, as many benign conditions may cause elevations in CEA. How often the test is done depends on many factors, but it is usually the change in CEA over time (serial CEA levels) that is most helpful.

Purpose of the Test

CEA is one 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 normal cells (and by the fetus during pregnancy), but is often produced in much larger amounts by cancerous tumors.

Uses/Indications

CEA may be drawn for a number of different reasons. Some of these include:

  • To monitor cancer treatment: If CEA levels are decreasing it usually means a tumor is responding to treatment, whereas 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 (metastases) to some regions of the body may cause much higher elevations of CEA, for example, metastases to the pleural cavity (with a malignant pleural effusion), peritoneal cavity (within the abdomen), or to 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: CEA levels cannot diagnose cancer, but are one puzzle piece that may raise suspicion.
  • In medical studies: A 2019 study 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 (CEA response was strongly linked with overall survival).

Carcinoembryonic antigen (CEA) is not used as a screening test for cancer for the general population but may be considered for people with some hereditary colorectal cancer syndromes.

Meaning of Carcinoembryonic Antigen (CEA)

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

The name "carcinoembryonic" refers to common sources of the protein, with "carcino" representing the tumors discussed and "embryonic" referring to the fact that high levels are present in the fetus during development.

Cancers Monitored with CEA

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

  • Colorectal cancer
  • Pancreatic cancer
  • Stomach cancer (gastric cancer)
  • Lung cancer
  • Breast cancer
  • Ovarian cancer
  • Thyroid (medullary) cancer
  • Bladder cancer
  • Head and neck cancer
  • Cervical cancer
  • Kidney cancer
  • Prostate cancer
  • Lymphoma
  • Melanoma

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 the early stages of the disease (this is one reason why it is 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 (non-cancerous) and inflammatory conditions that can increase CEA leading to false positive results.

Benign conditions associated with an increase in CEA levels include:

  • Smoking
  • COPD
  • Pancreatitis
  • Inflammatory bowel diseases such as Crohn's disease or ulcerative colitis
  • Hepatitis
  • Cirrhosis of the liver
  • Peptic ulcer disease
  • Gallbladder inflammation (cholecystitis)
  • Lung infections
  • Hypothyroidism
  • Colon polyps
  • Benign breast disease

In addition, CEA levels may not reflect what is happening with a tumor at the current time.

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

For example, CEA results may be very high during and after chemotherapy.

Similar Tests

There are a number of other tumor markers that may be drawn to monitor cancer, though the particular markers that are tested vary with the type of cancer being followed. An example of a few of these include:

  • 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

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.

Risks/Contraindications

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

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 a thoracentesis), or from the peritoneal cavity (via a paracentesis). The description below refers to having the test done the most common way; through a simple 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, and a tourniquet is applied. You may feel a sharp sting as the needle is introduced into the vein, and 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, and you should 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 to do the analysis. Possible side effects after the test (though very uncommon) 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 but should be repeated if abnormal to make sure it is a true result.

CEA levels are most helpful when repeated over time and seeing how they change.

In other words, "serial testing" gives more information than a single test.

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:

  • Less than or equal to 2.5 ng/ml (0 - 2.5) in nonsmokers
  • Less 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.

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

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.

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 3 months for at least 3 years after surgery. With treatment of metastatic colon cancer, in contrast, the test is often done every 1 month to 3 months.

Since levels can take some time to decrease during colon cancer treatment, it's important to consider the whole picture and not make treatment decisions based on the level of CEA alone.

A Word From Verywell

Carcinoembryonic antigen (CEA) is a useful test in monitoring cancer treatment, but it's important to note that it should not be used alone and is most helpful when looking at changes in the CEA over time rather than a single value. CEA levels are also helpful in predicting prognosis, but it's important to note that the prognosis of many cancers is changing with newer treatments, and statistics we have don't necessarily reflect those improvements.

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