The carcinoembryonic antigen (CEA) test checks the blood for CEA, a nonspecific cancer biomarker. Doctors who suspect a person may have colon cancer may order a CEA test to check for elevated levels of the antigen.

CEA in the blood can indicate the presence of cancer, but it cannot identify the exact cancer a person may have.

This article reviews how doctors may use the CEA test to diagnose colon cancer. It also discusses what a person can expect from the test and how it works.

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CEA is a type of glycoprotein found in the tubes of the digestive tract in developing fetuses. After birth, a person typically no longer has signs of CEA in their blood, but some will remain in their colon and other areas of their digestive tract.

Certain cancers, such as colon cancer, release CEA into the blood. An elevated blood level of CEA can indicate the presence of cancer, but the test is nonspecific. A doctor needs to order additional testing and review symptoms to determine what type of cancer a person may have.

A person undergoing cancer treatment may also benefit from the CEA test. When the test is done after cancer treatment, CEA in the blood can indicate cancer remains in the body.

The CEA test requires a blood draw.

A healthcare professional or phlebotomist typically takes about 3–5 cubic centimeters of blood from the arm using a needle or syringe. They then send the sample to a lab for analysis.

The lab sends a report with the estimated CEA content to the doctor. The doctor then reviews the results with the person.

A person does not need to take any action to prepare for the CEA test. It does not require fasting or other forms of preparation.

Before inserting the needle, a phlebotomist cleans the site of injection with an alcohol wipe or similar disinfecting wipe.

Following the blood draw, the technician sends the blood sample to a lab for analysis. The lab provides the doctor with an estimated CEA count in the person’s blood.

A doctor often schedules a follow-up appointment or provides another form of consultation when results come in.

Doctors cannot use the CEA test as a general screening because it does not provide information on the location or type of cancer a person may have. It also may not provide accurate CEA levels when checking for cancer recurrence due to low sensitivity.

If CEA blood levels are elevated, a doctor is likely to order additional testing, such as imaging tests, to determine the underlying cause of the elevated levels.

Even if CEA blood levels are not elevated, this does not rule out colon cancer. A doctor may still order additional tests if they suspect colon cancer.

In general, elevated CEA test results indicate the presence of cancer.

Normal ranges vary between people who smoke and those who do not.

For a person who does not smoke, a normal amount is less than or equal to 3 micrograms per liter (mcg/L). For a person who smokes, a normal amount is typically less than 5 mcg/L.

Elevated ranges can indicate localized or metastasized cancer and help predict outcomes. When a person’s range falls between 5 and 10 mcg/L, they may have a localized cancer with a low rate of recurrence.

A range greater than 10 mcg/L may indicate a poor outlook and a higher risk of recurrence.

When a person’s results may indicate greater than 20 mcg/L, their colon cancer has likely metastasized, or spread, to other areas of the body.

However, the results of a CEA test do not provide an accurate prediction of outcomes, tumor size, or whether the cancer has spread. For example, a person may have metastasized colon cancer and very low CEA levels.

Doctors and other experts generally consider blood draws safe and effective for most people. A person may experience minor pain at the site of injection. In rare cases, a person may develop an infection at the injection site.

The main risk of CEA testing involves the possibility of false results.

Some researchers suggest that, instead of a single value, doctors should retest and look for trends in CEA levels to help better assess treatment outcomes for colon cancer or other cancers.

A doctor may order a CEA test if they suspect colon cancer. The presence of CEA in the blood can indicate a tumor exists.

Some symptoms of colon cancer a doctor may investigate include:

  • abdominal pain or cramping
  • changes in bowel habits, such as constipation, narrowing stool, or diarrhea
  • unexplained weight loss
  • bleeding bright red blood from the rectum
  • bowel movement does not provide relief
  • fatigue
  • bloody stool
  • general weakness

Additionally, a doctor may order CEA testing after the treatment of colon cancer. Follow-up testing can help show whether the therapy successfully removed all cancerous cells. The continued presence of CEA could indicate some cancer remains.

A doctor may recommend regular follow-up screenings. According to a 2018 study, 5-year mortality did not change between people who received several tests throughout the first year following treatment and those who only received testing at 12 and 36 months.

Researchers did note that the higher testing group often caught the recurrence of cancer earlier, but it did not significantly improve their outcomes compared with the other group.

A CEA test does not specifically check for colon cancer or any other form of cancer. Instead, it can help indicate the presence of colon cancer, either as a new case or a recurrence.

To confirm the diagnosis, a doctor needs to order additional testing for colon cancer. Tests a doctor may order include stool tests and visual tests.

Some stool tests a doctor may order for testing for colon cancer include:

  • stool DNA test
  • guaiac-based fecal occult blood test (gFOBT)
  • fecal immunochemical test

Visual tests may include:

  • CT colonography
  • colonoscopy
  • flexible sigmoidoscopy

A person’s doctor can advise on what tests they order and what they involve.

The CEA test can help show the presence of certain cancers, such as colon cancer. However, it is nonspecific and cannot provide an accurate diagnosis of the cancer. A person can also have colon cancer without elevated CEA blood levels.

Still, doctors may order the test to determine whether an underlying cause of symptoms may be cancer or to check for recurrence of colon cancer. They are likely to order additional testing to further assess any elevated levels of CEA in the blood.

Doctors consider the test safe and minimally invasive with low risk and no need to take any special preparation to complete.