A stool DNA test uses a stool sample to look for signs of colon cancer. It's one option for colon cancer screening.

A stool DNA test finds cells in a stool sample. The test checks for changes in the cells' genetic material, which is also called DNA. Certain DNA changes are a sign that cancer is present or that it might happen in the future. The stool DNA test also looks for hidden blood in the stool.

If something concerning is found on your stool DNA test, you might need other tests. For instance, your health care provider will likely recommend a test to look at the inside of the colon, such as a colonoscopy.

One stool DNA test (Cologuard) is approved for colon cancer screening in the United States.

Why it's done

Stool DNA testing is used to screen for colon cancer in people with no symptoms. It also screens for growths of cells, called polyps, that could one day become cancer.

The stool DNA test looks for DNA changes and small amounts of blood shed into the stool. These might come from colon cancer or colon polyps.

When cancer or polyps are present in the colon, they continuously shed cells that have DNA changes into the stool. The DNA changes are found in very tiny amounts, so very sensitive lab tests are needed to detect them.

Research shows the stool DNA test is effective at detecting colon cancer and polyps that could become cancer. A positive test result usually requires a colonoscopy to examine the inside of the colon for polyps and cancer.

Stool DNA testing generally isn't used to test for colon cancer in people who have:

• Colon cancer symptoms, such as rectal bleeding, changes in bowel habits, abdominal pain and iron deficiency anemia
• A history of colon cancer, colon polyps or inflammatory bowel disease
• A strong family history of colon cancer, colon polyps or certain genetic syndromes that increase the risk of cancer

Risks

Risks and limitations of the stool DNA test include:

• The test isn't always accurate. It's possible for a stool DNA test to show signs of cancer, but no cancer is found with other tests. Doctors call this a false-positive result. It's also possible for the test to miss some cancers, which is called a false-negative result.
• Having a stool DNA test may lead to additional testing. If your stool DNA test result is positive, your health care provider may recommend a test to look at the inside of your colon. Often this is done with colonoscopy.

How you prepare

You don't need to do anything to get ready for a stool DNA test. You can eat and drink as usual before the test and use your current medications. There's also no need to undergo bowel preparation to clean out or empty the colon before the test.

What you can expect

During a stool DNA test you collect a stool sample. When you're done, you submit it to your health care provider's office or mail it to a designated laboratory.

You'll receive a stool DNA test kit for collecting and submitting the stool sample. The kit includes a container that attaches to the toilet. The kit also contains a preservative solution that you add to the stool sample before sealing the container. The stool DNA test requires only one stool sample.

Results

Stool DNA test results may include:

• Negative result. A test is considered negative if DNA changes and signs of blood aren't found in the stool. Your health care provider may recommend you repeat the test in three years.

• Positive result. A test is considered positive if DNA changes or signs of blood are found in the stool sample.

  Your provider may recommend additional testing to look for cancer or polyps in the colon. Usually this is with a colonoscopy.