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Side effects of screening colonoscopies

According to 'The Annals Of Internal Medicine,' the rate of serious complications from colonoscopy screening is “10 times higher than for any other commonly used cancer-screening test.” This number doesn't include deferred complications, such as internal bleeding, severe anemia, heart attack, stroke, pulmonary embolism, pneumonia, kidney failure, intestinal obstruction, and others.

These complications explain why, according to the Telemark Polyp Study I, colonoscopy screening increases relative mortality by 57%. Thus, if you are seriously considering to undergo screening, your odds of being killed or injured by the side effects of colonoscopy may actually exceed your odds of getting colorectal cancer in the first place [1].

Adding insult to injury, all that prep, fear, risk, expense, embarrassment, and stress are for naught anyway — screening colonoscopy offers near zero protection from colon cancer, as I explain in my Colonoscopy: Is it Worth the Risk report.

Miralax Safety Alert

What gives? Well, a conventional colonoscopy isn't simply a routine doctor's visit, but an ambulatory surgical procedure performed under general anesthesia. According to the same Annals of Internal Medicine, serious complications occur in 0.5% of all cases [link].

Unreported medical errors and deferred side effects, such as severe anemia caused by blood loss, pulmonary embolism, heart attack, or stroke related to blood clots caused by general anesthesia, pneumonia, persistent post-operative infection, or kidney failure and acute diverticulitis caused by colon prep, may easily add up to another percent or two.

If, for argument sake, the combined number of complications, side effects, and medical errors tally up to just 1%, it means that 140,000 people are injured annually by 14 million estimated screenings alone. This rate of “collateral damage” is just as high as the incidence of colorectal cancer itself, and, perhaps, is just as deadly, especially for seniors — a primary target group for “preventative” colonoscopies.

Even if you take at face value the claim that screening colonoscopies have reduced colorectal cancer mortality by 5% or about 2,500 lives annually, it means 56 people  have been needlessly harmed to save just one life (140,000 / 2,500).

Then, consider the 1 in 5 chance of getting any other cancer following a single virtual colonoscopy. Radiation exposure from just one abdominal CT scan (at 5 to 10 mSv) is two to three thousands times more potent than a single dental x-ray, and 2 to 3 times higher than the  estimated exposure to a “dirty” nuclear bomb estimated at just 3 mSv [link].

Cancer From Radiation Risk Estimates

As scary as the “dirty bombs” are, an explosion in the center of Fairfax County, VA, a populous suburb of Washington, DC, would affect only 19,500 people [link]. That is 50 to 100 times less people than are  being nuked annually in the radiology centers across the nation while administering unneeded and cancer-causing abdominal CT scans.

Since preventive colonoscopies became an outright fad after Ms. Couric‘s televised colonoscopy in March of 2000 [2], close to 30,000 more people annually have been affected by colon cancer.

Without a doubt, unnecessary screening colonoscopies — conventional and virtual alike, and almost all related to the Katie Couric Effect, — contribute to these new cancers by causing the following common side effects:

Common side effects of colonoscopy

The side effects of colonoscopy are similar to problems associated with any surgical procedure and are caused by the confluence of like factors: bowel prep, mechanical and surgical traumas by instruments, anesthesia, hypothermia, stress, opportunistic infections, fluctuations of blood sugar, excessive fluid consumption, sudden diet modification, and so on. Each stage introduces its own set of complications:

A few days following colonoscopy, side effects are commonly exacerbated by following routine advice to increase fiber intake. These complications may differ in nature depending on the degree of dysbacteriosis.

Patients with severe dysbacteriosis may not experience much if any bacterial fermentation of fiber and associated gases and bloating but may be affected by large stools, straining, constipation, hemorrhoids and obstruction. Those who retained some bacteria following the test may experience fermentation-related bloating, cramps and flatulence.

Post-traumatic stress syndrome (PTSS) is commonly associated with any invasive procedure in general and cancer screening in particular. It is especially bothersome among persons in a high-risk group or susceptible to anxieties and depression. PTSS commonly interferes with digestion because an elevated level of stress hormones and muscular tensions inhibit the secretion of digestive fluids and peristalsis.

Here is a specific list of the most likely side effects you may experience after the colonoscopy in (more or less) chronological order:

I realize the following two questions may be bugging you: (1) why aren‘t the complications described in this guide discussed with patients in advance of the screening? (2) Is it because doctors don‘t know?

I believe there are three factors behind this particular health scare:

Regardless of these reasons — some sinister, some stupid, some inadvertent to this situation — you now have the knowledge of what‘s causing them, how to avoid them and what to do about it.

What to do when you can't just say “no...”

In certain cases, colonoscopies are unavoidable, and, perhaps, life-saving. To protect yourself from unnecessary side effects, keep the following points in mind::

Dr_Whelch Should i be tested for cancer book coverFinally, If you are a physician or epidemiologist, and would like to get additional information about the perils of cancer (not just colorectal) screening, I recommend reading Dr. Gilbert Welch's book entitled Should I Be Tested for Cancer?  The answer to this question is quite self-evident from the subtitle: “Maybe Not and Here's Why!

Dr. Welsh — an ultimate insider — presents a good number of compelling reasons to explain why, in his own words “...cancer screening can do more harm than good”, and supports his analysis with detailed epidemiological data. 

According to Dr. Welch, the fear-mongering involved and risk of testing for other cancers are just as bad as for colon cancer. What else is new — where there is easy money to be made, victims are inevitable.

Author's commentaries

As you can see, a screening colonoscopy isn't the panacea it‘s purported to be. Be mindful of the risks; removing the causes of colon cancer should come first. And whether you do it or don't do it, it shouldn't be based on Ms. Couric‘s or my opinion, but on your doctor's weighted recommendation and/or risks factors discussed here.

Despite being well past 50, and in the high risk group for colorectal cancer, neither myself nor my wife Tatyana have ever been screened for colorectal cancer. We place more trust in functional nutrition and God's will than in “just in case” testing.

If and when we will take any test, we first must be darn sure that it's absolutely necessary. But as long as nothing hurts, we aren't into playing Russian roulette. I learned this rule a long time ago from an inside joke popular among physicians: “Should we treat him, or let him live?

It isn‘t as cynical as it may sound — medical doctors realize better than most that all medical procedures are inherently risky. Therefore, please don't interpret my analysis of screening colonoscopies as “Don't do it!”, but as “Don't overdo it!

Finally, if you do decide to get screened, at the very least you should restore intestinal flora after the procedure, as explained here. Otherwise you may be increasing your risk of developing new polyps and colorectal cancer long before the next screening is due in five or ten years, depending on your risk profile.


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The references for this guide were compiled in March 2008. Some of the links may not match at a later date because publishers may revise their web sites. In this case, try searching cached pages on Google, or contact the respective publishers.

1 Update on Colorectal Cancer; Am Fam Physician. 2000 Mar 15;61(6):1621-2, 1628 [link]

2 The Impact of a Celebrity Promotional Campaign on the Use of Colon Cancer Screening; The Katie Couric Effect; Archives of Internal Medicine, Vol. 163 No. 13, July 14, 2003 [link]

3Complications of Colonoscopy; Ann Intern Med. 2006 Dec 19;145(12):880-6 [link]

4 Assembly-line colonoscopies at clinic described; Las Vegas Sun, March 9, 2008 [link]

5 Whole Body Scanning Using Computer Tomography (CT); What are the Radiation Risks from CT; U.S. Food and Drug Administration, December 5, 2007 [link]

6 Virtual Colonoscopy Misses Nearly One Third of Lesions; The proceeds of the 68th annual scientific meeting of the American College of Gastroenterology; Oct 15, 2003 [link]

7 Irritable Bowel Syndrome; The National Digestive Diseases Information Clearinghouse, NIH Publication No. 07–693, September 2007 [link]