When I wrote about colonoscopy in 2010, colonoscopy was thought to be the best screening test for colorectal cancer because it could visualize the entire colon and could remove adenomas that were precursors of cancer. But only fecal occult blood testing (FOBT) and sigmoidoscopy had been proven to decrease colorectal cancer incidence and mortality (by 16% and 28%, respectively). Observational evidence suggested that colonoscopy would reduce the incidence and the number of deaths from colorectal cancer, but there were no randomized controlled trials, and the reduction in incidence of cancer after colonoscopy screening seemed to be restricted to left-sided colon cancers, which didn’t make sense.

We still don’t have any randomized controlled trials of colonoscopy, but a 2013 case-control study from Germany compared patients with and without colorectal cancer and found that those who reported having had a colonoscopy were less likely to develop colon cancer for up to 10 years after the procedure. And now two studies published in the New England Journal of Medicine in September 2013 have shed more light on the subject.

Sigmoidoscopy or colonoscopy vs. no screening

A large cohort study by Nishihara et al. looked at data from the Nurses’ Health Study and the Health Professionals Follow-up Study with a total of 88,902 subjects followed for 22 years. During that time, 1,815 colorectal cancers developed, and 474 subjects died from colorectal cancer. Those who had sigmoidoscopy or colonoscopy were much less likely to develop colon cancer than those who did not.

COLORECTAL CANCER Hazard ratio compared to no endoscopy
After polypectomy .57
After negative sigmoidoscopy .60
After negative colonoscopy .44
In right colon after negative colonoscopy .73
After sigmoidoscopy .59
After colonoscopy .32
From right colon cancer after colonoscopy .47
From right colon cancer after sigmoidoscopy No reduction

This is very encouraging. Colonoscopy cuts the incidence of colon cancer and of death from colon cancer by more than half. And it’s clearly superior to sigmoidoscopy in detecting cancers in the right side of the colon (proximal colon).

Usual care vs. fecal occult blood testing

The second study, by Shaukat et al. was a randomized controlled trial comparing usual care to annual or biennial screening with fecal occult blood testing (FOBT). It followed 33,020 subjects age 50-80 for 30 years. Annual screening reduced colorectal cancer mortality to a relative risk of .68; biennial screening to a relative risk of .78. All-cause mortality was not reduced. There was no benefit of screening below the age of 60 in women, although there was for men.

10% of participants had a positive FOBT at each screening, and 83% of those were further evaluated by colonoscopy, with polypectomy if polyps were detected. Long-term reduction of risk of death from colon cancer was consistent with the effect of removing adenomas that would have progressed to cancer and death.

It would not be appropriate to draw conclusions about the relative efficacy of FOBT vs. colonoscopy from these very different trials. There is still no evidence from randomized controlled trials directly comparing FOBT with colonoscopy, but such trials are in progress.

The recently introduced fecal immunochemical test (FIT) is more sensitive than the traditional guaiac test for FOBT, so it is likely that the results of fecal testing will improve. What we can say is that both types of screening are effective, and that the studies support current screening recommendations of FOBT annually, sigmoidoscopy every 5 years, or colonoscopy every 10 years from age 50 to 75. Patients can choose any of these after considering cost, complications, convenience, and other factors. Two other possible options are screening with barium enemas and virtual colonoscopy. Virtual colonoscopy (with CT) requires the same bowel prep as colonoscopy and if an abnormality is found, regular colonoscopy is still required for follow-up. Barium enemas miss about 50% of the cancers that can be found with colonoscopy. Both of those involve considerable exposure to radiation.

My colonoscopy experience (anecdote alert!)

I thought I would share my own colonoscopy experience for interested readers who want to hear a personal story about what it involves and what it’s like. If you’re not interested, just skip to the next heading. After reviewing the evidence and the pros and cons of each option, and considering my personal feelings about colonoscopy, I elected annual FOBT screening, and this year one of the three FOBT tests was positive for occult blood, so I had to bite the bullet and have a colonoscopy. It didn’t cost me anything, since as a military retiree I’m covered under Tri-Care for Life, but it was time-consuming. It involved 3 separate appointments on different dates: (1) with my primary provider to get a referral to the GI clinic; (2) in the GI clinic for pre-procedure history and physical and for education for informed consent (both by a physician assistant), and for instructions about the prep (by a nurse); and (3) for the procedure itself, which also required a time commitment from my husband who was required to be in the waiting room throughout the procedure and drive me home afterwards, since I couldn’t drive after IV sedation.

The thing I dreaded most was the bowel prep, and most people agree that’s the worst part of the procedure. I got a new and improved split-prep regimen. For 3 days before the colonoscopy I had to avoid high-fiber foods like popcorn, beans, seeds, multigrain bread, nuts, salad/vegetables, and fruit, which made meal planning a bit problematic. The day before colonoscopy, I was only allowed clear liquids, and was told to drink 8 ounces every hour, to include water, apple or white grape juice, broth, coffee or tea (without milk or cream), clear carbonated beverages, Kool-Aid (not red or blue), Jell-O (not red or blue), popsicles (not red or blue). They gave me a huge plastic jug with bowel prep powder with instructions to fill with water, mix, and keep refrigerated. Late in the afternoon on the day before colonoscopy, I had to start drinking an 8 oz glass of the bowel prep every 15-20 minutes until the level was down to a mark they had made on the jug. I was also instructed to continue hourly clear liquids up until midnight to prevent dehydration. On the morning of the colonoscopy I was instructed to skip my usual medications and drink the remaining solution, 8 oz. every 15-20 minutes, finishing 3 hours before leaving for my appointment. The solution didn’t taste very good, and it was difficult to force so much down in such a short time and the frequent intervals required watching the clock carefully or setting an alarm. I didn’t get nauseated, but I felt bloated and uncomfortable, and of course I spent quite a lot of time on the john including throughout the night (didn’t get much sleep). No cramps, just a lot of liquid, and it became hard to tell when I needed to get to the bathroom. By morning only clear liquid was coming out.

The procedure itself was a breeze. I was admitted with a patient wristband, given a hospital gown and an IV was started. There was a long wait, and eventually my gurney was rolled into the procedure room, where I was asked to lie on my side and given a sedative through the IV. The next thing I knew, I was waking up in the recovery area. They told me they had removed one small polyp, and the pathology results would be available in three weeks. I had no pain afterwards, didn’t even pass a lot of gas as they had warned I might. Went home and slept for several hours. My abdomen felt vaguely uncomfortable for about 3 days afterwards.

The polyp was a 4 mm adenoma, and they recommended a repeat colonoscopy in 5 years rather than the usual 10 year screening interval. I dreaded having to go through the bowel prep again, and in 10 years I would be past the upper age limit for screening. I discussed this with a gastroenterologist I knew, and he agreed with me that in my case my personal risk factors for colon cancer were so low that it would be reasonable to wait longer than 5 years, so with any luck I will never have another one. I sure hope I don’t. The whole rigmarole was unpleasant and complicated. I sure hope science and technology will come up with a better screening test sometime soon. There has to be a better way!

I certainly don’t regret getting it. I considered it medically necessary because of the positive FOBT, and I no longer have to wonder whether all is well in my colon. They got a good look throughout and removed the one small benign polyp. That’s very reassuring.

Pros and cons of colonoscopy

Colonoscopy is undoubtedly the best option for examining the entire colon and removing polyps that might develop into cancer. But there are risks: perforation of the bowel (in less than 0.2% of patients), bleeding, anesthesia complications, dehydration from the laxatives, rupture of the spleen (rare), infection, nausea, vomiting, allergic reactions, and even death (in 0.003-0.03% of patients). There is a substantial time commitment and an average cost of over $1,185 in the US. The total cost to insurance companies and the government must be staggering. There is inconvenience, time lost from work, and an arduous bowel prep. There are not enough colonoscopists to screen the entire population as recommended. A gastroenterologist can spend a huge chunk of his time doing these routine screening procedures. According to a British report, clinicians did up to 448 a year, with an average of 205. I’d think a gastroenterology subspecialist would get bored and feel frustrated that after his 14 to 15 years of education after high school, he was spending so much time on such a routine procedure. As the population ages and the demand for colonoscopies increases, I wonder whether it wouldn’t make more sense to train PAs (physician assistants) to do the job. It’s basically a matter of manual skills, coordination, and practice, and I think PA’s could be taught to do it as competently and safely as MDs, and doctors could be on standby to assist in managing any complications that developed. It would save money and leave the gastroenterologists free to exercise the clinical expertise that they have trained so long to attain.


New evidence supports the current recommendations for colorectal cancer screening. Screening by either FOBT, sigmoidoscopy, or colonoscopy significantly reduces the incidence of colorectal cancer and the death rate from colorectal cancer. We still don’t have evidence to directly compare the effectiveness of the different options or to show a decrease in all-cause mortality. Trials are in progress that should provide that evidence. Meanwhile, if you are approaching the age of 50, you have a decision to make: not whether to be screened, but which screening test to choose.

Posted by Harriet Hall

Harriet Hall, MD also known as The SkepDoc, is a retired family physician who writes about pseudoscience and questionable medical practices. She received her BA and MD from the University of Washington, did her internship in the Air Force (the second female ever to do so),  and was the first female graduate of the Air Force family practice residency at Eglin Air Force Base. During a long career as an Air Force physician, she held various positions from flight surgeon to DBMS (Director of Base Medical Services) and did everything from delivering babies to taking the controls of a B-52. She retired with the rank of Colonel.  In 2008 she published her memoirs, Women Aren't Supposed to Fly.