Colonoscopy: Extremely Beneficial—Extremely Avoided

FEBRUARY 01, 2008
Guido R. Zanni, PhD

Dr. Zanni is a psychologist and health-systems specialist based in Alexandria, Virginia.

Colorectal cancer (CRC) is the second leading cause of cancer deaths in the United States, resulting in an estimated 57,000 deaths annually.1,2 Although CRC is among the most preventable cancers, <43% of Americans aged 50 years and older adhere to the recommended screening guidelines.3 The 5-year survival rate is 90% with early detection of this slow-growing cancer; however, 61% of CRC cases are identified after it has metastasized.4

Screening Guidelines

Colonoscopy is the preferred CRC-screening procedure. Research demonstrates its improved accuracy in detecting adenomas (precancerous polyps), compared with other procedures. For example, fecal occult blood testing alone is insufficient; patients with adenomas often test negative.5

The American College of Gastroenterology (ACG) issued CRC-screening guidelines (Table) in 2000 that vary according to the following risk categories5:

  • Average risk—patients aged 50 and older, lacking other risk factors
  • Moderate risk—patients with a single first-degree relative who was diagnosed with CRC at age 60 or older, or patients with first-degree relatives with adenomas diagnosed before age 60
  • High risk—patients with multiple first-degree relatives with CRC or a single first-degree relative with CRC who was diagnosed before age 60; or patients with families with the rare syndromes of familial adenomatous polyposis and hereditary nonpolyposis CRC or with a history of polyps, Crohn's disease, or ulcerative colitis6

The ACG recommends physicians modify guidelines consistent with the strength of known risk factors and medical histories.


Understanding Nonadherence

Surveys reveal that patients find the preparatory regimen the most objectionable aspect of colonoscopy.7 Some patients fail to complete the preparation process because of adverse effects experienced with the prescribed purgatives.6 Colonoscopy's invasiveness is another factor fueling nonadherence; 1 survey found most patients would readily accept noninvasive procedures (eg, computed tomography scans) but are less agreeable to invasive procedures.8 Finally, some patients refuse screening because of negative reports received from their families and friends.

Bowel Preparation

Bowel preparation formulations are either glycol-electrolyte lavage solution formulations (eg, Golytely, Colyte, TriLyte, HalfLytely with bisacodyl tablets, Movi-Prep) or sodium phosphate preparations, available in tablet and liquid formulations (eg, Fleet Phospho-soda, Fleet Accuprep, Visicol tablets, Osmoprep tablets). Dosages vary among products; patients must follow directions precisely.

Common side effects for both formulation categories include nausea, vomiting, abdominal cramping, and bloating. Some studies report fewer side effects with sodium phosphate tablets.6 Rare side effects include bleeding in the mucous membrane that connects the esophagus to the stomach, esophageal perforation, toxic colitis, medication malabsorption, pulmonary aspiration, hypothermia, cardiac arrhythmias, pancreatitis, inappropriate antidiuretic hormone secretion, and renal failure. Some extremely rare adverse reactions resulted in patient fatalities.6

Proper hydration is required before, during, and after colonoscopy to avoid electrolyte imbalances. Although dehydration is a significant component underlying some of the most serious adverse effects, clinicians often forget to counsel patients about volume repletion. It may seem counterintuitive that dehydration can occur when consuming 4 L of fluid; however, large amounts of fluids are required to evacuate the colon. These fluids, along with fluids in undigested food, are eliminated.


The ACG notes that decreasing dietary animal fat, increasing vegetables and dietary fiber, and increasing calcium and folic acid may help prevent colon cancer, but further study continues.2 A recent review of >7000 studies concludes that heavy consumption of red meat, especially processed meat (eg, sausage, ham, salami) increases CRC risk, as do poor diets, physical inactivity, and obesity. The same review recommends consuming <18 oz of red meat per week.10


Researchers are refining diagnostic alternatives, and the virtual colonoscopy holds promise for the future. Until then, health professionals must promote the importance of colonoscopy. Some patients find the topic difficult and embarrassing to discuss and feel more comfortable with written information. The National Institute of Diabetes and Digestive and Kidney Diseases publishes an excellent, easy-to-understand brochure on colonoscopy that can be found at Many patients take complimentary copies placed on the counter; therefore, this method is recommended.


  1. Jemal A, Siegel R, Ward E, et al. Cancer statistics, 2007. CA Cancer J Clin. 2007;57:43-66.
  2. American College of Gastroenterology. Colon cancer screening and prevention. Accessed November 27, 2007.
  3. Seeff LC, Nadel MR, Klabunde CN, et al. Patterns and predictors of colorectal cancer test use in the adult U.S. population. Cancer. 2004;100:2093-2103.
  4. Ries LAG, Harkins D, Krapcho M, et al (eds). SEER Cancer Statistics Review, 1975-2003, National Cancer Institute. Bethesda, MD,, based on November 2005 SEER data submission, posted to the SEER web site, 2006. Accessed November 27, 2007.
  5. Rex DK, Johnson DA, Lieberman DA, Burt RW, Sonnenberg A. Colorectal cancer prevention 2000: screening recommendations of the American College of Gastroenterology. American College of Gastroenterology. Am J Gastroenterol. 2000;95:868-877.
  6. Lichtenstein GR, Cohen LB, Uribarri J. Review article: Bowel preparation for colonoscopy--the importance of adequate hydration. Aliment Pharmacol Ther. 2007;26:633-641.
  7. Harewood GC, Wiersema MJ, Melton LJ 3rd. A prospective, controlled assessment of factors influencing acceptance of screening colonoscopy. Am J Gastroenterol. 2002;97:3186-3194.
  8. Marshall DA, Johnson FR, Phillips KA, et al. Measuring patient preferences for colorectal cancer screening using a choice-format survey. Value Health. 2007;10:415-430.
  9. U.S. Food and Drug Administration. FDA alert - oral sodium phosphate (OSP) products for bowel cleansing. www.fda/gov/cder/drug/infopage/OSP_solution/default.htm. Accessed November 30, 2007.
  10. World Cancer Research Fund, American Cancer Institute. Food, Nutrition, Physical Activity, and the Prevention of Cancer: a Global Perspective. Accessed November 29, 2007.