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Can You Really Poop in a Box to Prevent Colon Cancer?

You may have seen the TV commercials: There’s a new at-home colon cancer test called Cologuard that detects colon cancer. If you’re nervous about getting a colonoscopy, you may be wondering if this at-home test is a better alternative.

UNC gastroenterologist Rig Patel, MD, the medical director of REX Digestive Healthcare, tells us the pros and cons.

How Cologuard Works

Your primary care physician orders the test, and a kit is shipped to your home. You collect a stool sample and mail it to a lab in a pre-addressed box. The lab will send results to your physician within two weeks. It costs about $600. Insurance may cover some or all of that amount.

“It’s an easy test, and you can do it at home, but you have to collect a full stool sample and send the kit in the mail to the company. Not everyone’s comfortable with that,” Dr. Patel says.

The company tests the DNA and blood cells in the sample to determine if you have colon cancer or an advanced polyp.

“In studies, it did pick up cancers with a good sensitivity, just over 90 percent—that is, if you’ve already got cancer or you’ve already got an advanced polyp,” Dr. Patel says.

If it’s positive, you need a colonoscopy to definitively diagnose a polyp or cancer by biopsy. However, Cologuard can have false positive results (in some studies nearly 10 percent), meaning the test indicates you have cancer, but those findings are false. A colonoscopy is needed to reach a definitive diagnosis.

Cologuard vs. Colonoscopy

While the Cologuard can detect cancer or an advanced polyp, its accuracy in detecting small polyps is not good, Dr. Patel says.

Colon cancer starts when you develop a small polyp, or growth, on the inside of the colon. Over time, that polyp gets bigger. The larger it gets, the higher the risk it will turn into cancer. The way you prevent colon cancer is by detecting and removing polyps in the colon before they become cancerous, and colonoscopy is the only way to do that.

“We like to find the polyps when they’re ‘young’ and small because they are easy to remove and completely benign,” Dr. Patel says. “The stool tests detect polyps that are older, more advanced or already have turned into cancer. A negative Cologuard doesn’t mean you don’t have small polyps.”

So the Cologuard is detection but not prevention. A colonoscopy does both. Plus, if your Cologuard test detects a possible cancer, you’ll need a colonoscopy anyway.

“If the Cologuard comes back positive and then they go for a colonoscopy, the colonoscopy is no longer a screening colonoscopy,” Dr. Patel says. “They’re having it because they have a positive Cologuard, and the insurance companies look at that differently and it may no longer be covered as a preventive test if performed after a positive stool test.”

In addition, you need to have a Cologuard test every three years. If you have a negative colonoscopy (and have no high-risk factors for colon cancer, such as family history), you’re good for 10 years.

Best Candidates for Cologuard

A colonoscopy can carry greater risks of complications for patients who are at higher risk when under sedation, including people with significant heart or lung disease. Cologuard might be a good idea for those high-risk patients, Dr. Patel says.

But for most people, colonoscopy is best.

“Any time you do a screening, you want to minimize risk,” Dr. Patel says. “A colonoscopy is an invasive procedure, and one has to be careful. But the complication rate is low enough, though, that it’s still regarded as the most effective screening test for most people.”

Despite the limitations of Cologuard, Dr. Patel would rather a patient do an at-home test than skip a screening.

“Any screening is better than no screening,” he says. “So if people are not going to get a colonoscopy, they should definitely have a stool test.”


If you have concerns about colon cancer, talk to your doctor. If you do not have a doctor, find one near you.