Stool DNA test for colon cancer FAQ

By Mayo Clinic Health System staff

Colorectal cancer is the second leading cause of cancer death among men and women. According to the American Cancer Society, more than 140,000 people will develop colorectal cancer in 2018, and more than 50,000 will die of the disease. Fortunately, when detected early, the five-year survival rate can be greater than 90 percent.

One newer method of detection is a stool DNA test, called Cologuard. It offers people age 50 and older who are at average risk for colorectal cancer an easy to use a screening test they can do in the privacy of their own home.

What is it?

The stool DNA test is a noninvasive test to screen for colon cancer. It identifies DNA changes in the cells of a stool sample and looks for abnormal DNA associated with colon cancer or polyps. The test also detects hidden blood in the stool, which can indicate the presence of cancer.

Why is it done?

Stool DNA testing is intended to screen for colon cancer or precancerous polyps in people with no symptoms. The test detects abnormal DNA and small amounts of blood shed into the stool from colon cancer or polyps. When present in your colon, cancer or polyps continuously shed cells with abnormal DNA changes into the stool. The DNA changes are found in tiny amounts, so sensitive laboratory methods are required to detect them.

Research shows the stool DNA test is effective at detecting colon cancer and precancerous polyps. The test is not for everyone and is not a replacement for colonoscopy if you have had an abnormal colonoscopy in the past or a family history of colon cancer.

What are the risks?

The stool DNA test is safe and poses no risks.

How do you prepare?

Here’s the good news: The test requires no preparation or anesthesia. Before the test, you can eat and drink normally and take your current medications. There's no need to undergo bowel preparation to clean out or empty your colon prior to taking the test.

What can you expect?

You will 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 you add to the stool sample before sealing the container. The test requires only one stool sample.

After the stool sample is collected, it is returned to the company via UPS in a prepaid box.

What do the results mean?

Results may include:

• Negative result — A test is considered negative if there are no abnormal DNA changes common to colon cancer or precancerous polyps and signs of blood found in the stool. Your doctor may recommend you repeat the test in three years.
• Positive result — A test is considered positive if abnormal DNA changes common to colon cancer or precancerous polyps or signs of blood are found in the stool sample. A positive test is typically followed by a colonoscopy to examine the inside of the colon to determine if cancer or polyps are present.

For every 20 people who undergo stool DNA testing, one or two will have a positive result, but no cancer or polyps will be found during a follow-up colonoscopy. Your doctor would discuss follow up in this circumstance.

This new test may move more people to get screened earlier — a critical step in beating this common and preventable cancer — but remember, it is important to talk to your doctor about the best option for you.