The stool DNA test is a noninvasive laboratory test that identifies DNA changes in the cells of a stool sample. The stool DNA test specifically looks for DNA alterations associated with colon polyps and colon cancer.
The major goal of the stool DNA test is to detect whether DNA changes that indicate colon cancer or precancerous polyps are present in the colon.
One stool DNA test (Cologuard) is approved for use the United States.
Why it's done
Stool DNA testing is intended to screen healthy people with no symptoms for colon cancer or precancerous polyps. The test also measures blood in the stool. Research shows the stool DNA test is effective at detecting colon cancer and precancerous polyps.
How stool DNA testing works
The stool DNA test detects signature DNA changes in tumor cells that are found in the stool.
Because the lining of the colon is always shedding cells, including cells from the surface of polyps and cancers, these markers are available in the stool. A stool DNA test can identify several of these markers, indicating the presence of precancerous polyps or colon cancer.
Many different DNA changes may be present in colon cancer cells, so the stool DNA test looks for a panel of DNA markers. Also, because DNA markers may be present in only tiny amounts in stool, very sensitive laboratory methods are required.
The stool DNA test is safe and poses no risks.
Limitations of the test may include:
A stool DNA test could lead to additional testing. If your stool DNA test shows DNA changes that are associated with colon polyps or colon cancer, you'll likely undergo additional testing to find the source.
Your doctor would likely recommend colonoscopy, which includes removal of polyps or biopsy procedures to remove tissue samples for testing. If you undergo these additional tests, but it's determined that you don't have cancer, you could be exposed to additional risks for no reason.
- A stool DNA test can't detect all cancers. It's possible that colon cancer or precancerous polyps could go undetected during a stool DNA test. This might occur due to a technical error or to insufficient quantity of your stool sample.
How you prepare
Stool DNA testing requires little preparation. You can eat and drink normally before the test and continue your current medications. There's also no need to undergo bowel preparation to clean out or empty your colon before the test.
What you can expect
During a stool DNA test you collect a stool sample and submit it to your doctor'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 and a preservative solution that is added to the stool sample before sealing the container. The stool DNA test requires only one stool sample.
After the stool sample is collected, it can be returned to the doctor's office or sent by mail to the laboratory.
Stool DNA test results may include:
- Negative result. A test is considered negative if DNA markers common to colon cancer or precancerous polyps and signs of blood are not found in the stool.
- Positive result. A test is considered positive if DNA markers common to colon cancer or precancerous polyps or signs of blood are found in the stool sample. Additional evaluation, such as a colonoscopy to examine the colon, may be recommended to determine the cause.