Laxative-free colonoscopy on the way?

For many people, the most unpleasant part of having a colonoscopy is the aggressive bowel-cleansing prep the day before. In tomorrow’s Annals of Internal Medicine, Harvard researchers report a laxative-free version of “virtual colonoscopy,” an established procedure that uses a CT scan instead of a ‘scope to check the colon for cancers and precancerous polyps.

At present, virtual colonoscopy requires a full bowel prep to make the colon wall visible to the CT scan. But a new, experimental version does it digitally. The team, led by Dr. Michael Zalis of Harvard-affiliated Massachusetts General Hospital (MGH), used sophisticated computer software to make stool in the colon disappear — akin to Photoshopping blemishes from still photos.

Reluctance to undergo the bowel prep hinders more widespread testing for cancer and precancerous polyps. According to the American Cancer Society, colorectal cancer screening rates hover around 50% in some states. Virtual colonoscopy without a day-long bowel prep beforehand could help remedy the problem.

“Laxative-free CT colonography has the potential to reach some of the unscreened population and save lives,” says Dr. Zalis, an associate professor of radiology at MGH and director of CT colonography at MGH Imaging.

Aversion to colon prep

Public health guidelines urge people 50 or older to be checked for colon cancer and polyps. There are several options, including a simple stool test. But the gold standard is colonoscopy using a flexible, lighted instrument called a colonoscope. A doctor looks through the colonoscope and inspects the colon. If he or she finds a pre-cancerous polyp, a device on the end of the colonoscope is used to remove it from the colon wall. Removing precancerous growths helps prevent cancer, and research strongly suggests it prevents premature deaths from colon cancer—a critical test for any screening method to pass.

Colonoscopy’s ability to both find and remove polyps is an advantage over other screening options. “The trouble is a lot of the people at risk of colorectal cancer have a strong aversion to the laxative prep that is required for colonoscopy,” Dr. Zalis told me.

Enter laxative-free virtual colonoscopy, known in the medical world as CT colonography or CTC.

An experimental version of the virtual colonoscope digitally removes stool from the colon, allowing doctors to see polyps and other abnormalities. (Photo courtesy Dr. Michael Zalis.)

Colon photoshopping

In the study, Zalis and his colleagues recruited 605 volunteers at four medical centers, including MGH and nearby Brigham and Women’s Hospital. For two days before the their scans, the volunteers drank small amounts of a contrast agent with meals. This chemically “tagged” the stool, allowing software to detect it and subtract it from the CT scan. What remained was a 3D image of the colon wall that radiologists then searched for polyps, as shown in the image to the right.

The laxative-free method identified 91% of the people with precancerous polyps that were 1 centimeter or larger, which is about as accurate as conventional colonoscopy. Zalis says that more than 90% of polyps that develop into cancer are 1 centimeter or larger.

Two factors that limit virtual colonoscopy’s wider adoption today are that it still requires a colon prep and, if polyps are discovered, you still need to have a full colonoscopy. Laxative-free CTC removes one of those limits.

Larger studies are needed to fully understand the potential of laxative-free CTC, but the latest research is an important step toward expanding colorectal cancer screening to people who would otherwise put it off or avoid it entirely—and put themselves at higher risk of developing colon cancer or dying prematurely. “The study opens the door to a laxative-free and more patient-friendly version of colon cancer screening,” Dr. Zalis says.

Related Information: Harvard Men’s Health Watch


  1. Tama Schlemmer

    This new prep-free colon scan can’t come soon enough for me!! Was diagnosed with Crohn’s disease at 30yrs old and have not had regular colonoscopies because as I get older, each time I try to do prep I get very ill throwing up etc… I know many others who have had just one colonoscopy and vow they will never do it again because they bacame so ill from the prep too. Please hurry with this technology many are in desperate need of it!

  2. Brian Collins

    Dear Colonoscopy Cohorts,

    I’d like to tell you my colonoscopy story in case you face these same challenges.

    About 15 years ago, I had my first colonoscopy (they are a piece of cake really), and the doctor found hundreds of polyps, but fortunately, no cancer. The general consensus (I got second, third and fourth opinions) was that I needed to have my colon removed (colectomy), as was standard procedure at the time. I did a lot of research, including speaking with those who had gone through a colectomy, and found that their quality of life had seriously diminished after the surgery. So my gastroenterologist suggested that we just go in every couple of months and remove as many polyps as possible in each two-hour session until they were all gone. We followed that path for two years before all the polyps had been removed. Then we went to a once a year schedule, and finally, now, are doing a colonoscopy every two years. Thus far, it’s worked like a charm.

    No one could figure out why I continued to grow polyps, but since their numbers were under control, I figured that I could live with a scope every two years, when about 30 new polyps would be removed.

    But I decided to do some experimenting with my diet, minimizing my intake of dairy, sugar, and gluten (found in wheat products) to see if the number of polyps would go down every two years. What I found out was that for me, the elimination of dairy and sugar didn’t make much difference. But when I eliminated gluten from my diet – very easy to do these days with all of the substitutes, including gluten-free beer – the number of new polyps removed went from about 30 four years ago, down to five two years ago, down to one last week. For me, gluten seems to be the trigger.

    Here’s your takeaway from the above info:

    1. Having large numbers of polyps doesn’t necessarily mean that you have to have your colon removed. And
    2. Removing gluten from your diet could diminish the number of new polyps, and reduce your chance of contracting cancer.

  3. Darrel Fredrick

    I think this will be better for a lot of people it’s always good to see medical working to help others. I wonder how long before this makes it’s way into doctors offices around the US.

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