Screening Colonoscopy Reduces Deaths from Colorectal Cancer

Colonoscopy explained, understand the risks and benefits and answers to frequently asked questions about colonoscopy.

Medically reviewed by Dr. C.H. Weaver M.D. Medical editor 3/2019

A colonoscopy is the preferred method for detecting early colon cancer and is recommended every 5-10 years beginning at age 40-50 years for average-risk individuals. During a colonoscopy, a flexible tube attached to a camera is inserted through the rectum, allowing physicians to examine the internal lining of the colon and rectum for cancer or precancerous polyps. If polyps are identified, they can be removed during the colonoscopy.

According to the results of a study published in the New England Journal of Medicine, the identification and removal of polyps during screening colonoscopy substantially reduces the risk of death from colorectal cancer, providing support for use of colonoscopy as a colorectal cancer screening test. The study evaluated information from 2,602 people who had precancerous (adenomatous) polyps removed during colonoscopy. During more than 15 years of follow-up, people who had had colorectal polyps removed during colonoscopy were roughly half as likely to die of colorectal cancer as people in the general population.(1)

What to Expect During a Colonoscopy

The anticipation of colonoscopy is often worse than the actual exam. Knowing what to expect can eliminate unnecessary anxiety. There are two phases of colonoscopy: the preparation and the exam.

Preparation: Bowel preparation (cleansing) is a critical component of the procedure. It is important to clean out the colon completely because any residue can obscure the view of the colon and rectum during the exam. Bowel preparation varies slightly among different medical centers, but in general here’s what you can expect:

  • Five days before exam: Stop eating nuts and seeds. Stop taking iron supplements.
  • Two days before exam: Avoid vegetables, pulpy fruits, oatmeal and cereal with high fiber, nuts, and small seeds such as sesame seeds.
  • 24 hours before exam: Switch to a clear-liquid diet. Avoid solid food and alcohol until after the exam.
  • Bowel cleansing: The physician will prescribe a liquid cleansing solution that you will drink the evening before the exam. You’ll want to drink plenty of water and stay near the bathroom. Numerous trips to the bathroom can cause anal irritation. Speak with your doctor or nurse about tips for managing this irritation. Sometimes wiping with medicated wipes or swabbing the anus with petroleum jelly can help.

The Exam: The colonoscopy exam will take anywhere from 20 to 60 minutes. When you arrive at the medical center, you’ll sign consent forms and change into a hospital gown. In the exam room, you will be hooked up to an intravenous (IV) line as well as blood pressure and blood oxygen monitoring devices. The physician will deliver pain relievers and a sedative through the IV.During the procedure you’ll be in “conscious sedation,” which is a pleasant, relaxed state in which you don’t feel a thing. In fact, you will likely have no memory of the procedure itself.

After the Exam: After the procedure you’ll be moved to a recovery room, where the IV is removed and you are given time to wake up. Most people feel fine after waking up. You might feel woozy or have a dry mouth, and you may have some gas that causes mild discomfort. You’ll be able to walk out of the medical center on your own, but you’ll need someone to drive you home as a result of the sedation. In fact, you’ll want to take it easy and avoid driving for the rest of the day.

Following a normal colonoscopy, how often should a colonoscopy be performed?

Individuals who have normal results on their colonoscopy don’t need to undergo another colonoscopy for at least 5 years according to a report published in the New England Journal of Medicine.

Researchers from Indianapolis conducted a clinical trial to evaluate the time interval between repeat colonoscopies among patients with normal results from an initial colonoscopy. This trial included 1,256 individuals who underwent rescreening at an average of 5.34 years following their original colonoscopy.

  • None of these patients had colorectal cancer identified on their follow-up colonoscopy.
  • 16% of patients had non-cancerous tumors on repeat colonoscopy; however, advanced non-cancerous tumors were found in only 1.3% of patients.

The researchers concluded: “Our findings support a rescreening interval of 5 years or longer after a normal colonoscopic examination.” All patients, however, should discuss their individual risks and benefits of repeat colonoscopy screening.(2)

Follow-Up Colonoscopies Underused After Polypectomy

Follow-up colonoscopy remains significantly underused in the 5-year interval after a polypectomy (removal of polyps).

Cancers of the colon and rectum, sometimes referred to together as colorectal cancer, often begin with the development of an adenomatous polyp. These polyps often take 10 to 15 years to transform into cancer.

Recommendations vary, but in general, individuals who have polyps removed are recommended to undergo a follow-up colonoscopy in five years. In order to measure adherence to this recommendation, researchers used data from Medicare claims in 12,998 patients aged 71 and older with a claim for colonoscopy with polypectomy or hot biopsy from 2001 to 2004. In addition, the researchers evaluated Medicare claims from the previous five years to obtain data about previous examinations, and to estimate a comorbidity score.(3)

The results indicated that at the end of the five-year follow-up period, only 33.5 percent of patients had received another colonoscopy and 24.2 percent underwent repeat polypectomy. The results were in startling contrast to what the researchers expected, which was an overuse of colonoscopy. Instead, they found a significant under use of follow-up colonoscopy.

In general, patients with an identified history of polyps should come back in five years, but the researchers found that only about one-third of patients adhere to that recommendation.

Does colonoscopy ever miss cancers?

Colonoscopy may miss more colon cancers than once believed, particularly small cancers in the fold of tissues or at the anal entrance. Previous studies evaluating virtual colonoscopy always compared results of the procedure to optical colonoscopy. In a clinical study 1,233 participants underwent both optical colonoscopy and virtual colonoscopy and results were compared for both types of procedures.

Prior to the study, it was believed that the miss rate of lesions >1cm with optical colonoscopy was 0-6%. After both optical and virtual colonoscopy, results were evaluated and it was determined that approximately 10% of polyps were missed by optical colonoscopy. The majority of these polyps were located on a fold in the tissue or near the anal entrance. Despite these findings, however, optical colonoscopy remains the gold standard for detecting and diagnosing colorectal diseases and significantly improves survival in colorectal cancer when used as a screening tool.(4)

Does physician experience matter?

Physicians with more training perform more effective colonoscopies. A trial conducted at 15 different medical centers in Korea indicates that a physician must perform at least 150 colonoscopies to be considered competent at the procedure. Various medical training programs currently recommend that trainees perform at least 100–200 colonoscopies in order to be considered competent in screening and diagnostic colonoscopy.

In the current study, researchers sought to further define the adequate training level for technical competence in performing colonoscopy. During an eight-month period, 24 first-year gastroenterologist trainees (fellows) in 15 medical centers were evaluated. A total of 4,351 colonoscopies were performed and evaluated during this time period. The goal of the study was to evaluate the success rate for completing the colonoscopy and performing colonoscopy in less than 20 minutes.(5)

  • Results of the study revealed an overall success rate of 83.5%.
  • Success rates were notably improved after 150 procedures, rising incrementally from 71.5% to 98.7% after each 50 cases.

Researchers concluded that competent screening and diagnostic colonoscopy generally requires that physicians have performed at least 150 cases. Patients planning to undergo colonoscopy may wish to inquire about their physician’s level of experience.

What are the risks associated with colonoscopy?

Perforation (a tear through the colon wall caused by a colonoscopy procedure) occurs in less than one in 1,000 patients undergoing a colonoscopy according to researchers from the Mayo Clinic who evaluated data in an attempt to understand the rate of perforations associated with colonoscopies. The data included 258,248 colonoscopies.

  • The rate of perforation was only 0.7%.
  • Blunt injuries, poor bowel preparation, corticosteroid use, and younger age increased the incidence of adverse effects associated with colonoscopy.

These data indicate that the risk of perforations during a colonoscopy remains very low, but that the risk factors associated with perforations are important to understand. Patients with any of the factors associated with an increased risk of perforation may wish to speak with their physician regarding their individual risks and benefits of undergoing a colonoscopy.(6)

Anesthesia Increases Colonoscopy Risks

Colonoscopy can be performed with anesthesia or without and a study published in the journal Gastroenterology has reported that sedation increases the risk of complications.(7)

The study authors analyzed administrative claims data from Truven Health Analytics MarketScan Research Databases from 2008 through 2011 and identified 3,168,228 colonoscopy procedures in men and women, aged 40–64 years old. Colonoscopy complications were measured within 30 days and included colonic (ie, perforation, hemorrhage, abdominal pain), anesthesia-associated (ie, pneumonia, infection, complications secondary to anesthesia), and cardiopulmonary outcomes (ie, hypotension, myocardial infarction, stroke).

Nationwide, 34.4% of colonoscopies were conducted with anesthesia services. Anesthesia use was associated with a 13 percent increase in the risk of any complications. The increased risk was associated specifically with an increased risk of perforation, hemorrhage, abdominal pain, complications secondary to anesthesia, and stroke.

The study authors concluded that the overall risk of complications after colonoscopy increases when individuals receive anesthesia services. The widespread adoption of anesthesia services with colonoscopy should be considered within the context of all potential risks and patients should discuss the risks and benefits of using anesthesia during colonoscopy for their situation.

Age and Illness Increase Colonoscopy Risks

Although the risk of complications from colonoscopy is low, risk increases among the very elderly and among those with certain chronic health conditions.(8)

To explore the safety of colonoscopy and whether safety varies by the age and health of the patient, researchers evaluated information from 53,220 Medicare beneficiaries aged 66 to 95 who underwent colonoscopy.

The researchers found that a serious gastrointestinal event (perforation or bleeding within 30 days of colonoscopy) occurred in 6.9 per 1,000 colonoscopies. Although this risk was low, it varied by age. The risk of a serious gastrointestinal event was more than twice as high among persons aged 85 and older than among persons between the ages of 66 and 69.

These results are consistent with recommendations from the U.S. Preventive Services Task Force (USPSTF). The USPSTF recommends against colorectal cancer screening among adults over the age of 85 because the risks are likely to outweigh the benefits.

In addition to varying by age, the risk of serious gastrointestinal events also varied by the health of person being screened. People with a history of stroke, chronic obstructive pulmonary disease, atrial fibrillation, or congestive heart failure were more likely than people without these conditions to experience a serious gastrointestinal event following colonoscopy.

This study suggests that the overall risk of colonoscopy complications among Medicare beneficiaries is low. Nevertheless, risk increases with age and with certain chronic health problems. People who are candidates for colorectal cancer screening may wish to talk with their doctor about which colorectal cancer screening test is best for them.

Very Elderly May Derive Less Benefit from Colonoscopy

According to the results of a study published in the Journal of the American Medical Association, the increase in life expectancy that results from screening colonoscopy is smaller for very elderly patients than for younger patients.

Colorectal cancer is the second leading cause of cancer-related deaths in the U.S. The disease develops in the large intestine, which includes the colon (the longest part of the large intestine) and the rectum (the last several inches).

Cure rates for colorectal cancer are high when the disease is detected and treated early. Currently, it is recommended that people 50 years of age or older and those at a high risk for colorectal cancer be screened for the disease.

Screening methods include testing for blood in the stool (fecal occult blood test), flexible sigmoidoscopy, colonoscopy, and barium enema. Colorectal cancer screening can detect cancer at an early stage, and can also prevent cancer by allowing physicians to detect and remove precancerous polyps.

During a colonoscopy, a lighted instrument called a colonoscope is used to view the rectum and the entire colon. Pictures and samples of tissue (biopsies) may be taken for further evaluation by the physician. Because colonoscopy has been reported to have a higher complication rate in very elderly patients, and because very elderly patients have a shorter life expectancy than younger patients, it’s possible that very elderly patients will derive fewer benefits from screening colonoscopy than younger patients.

To compare the effect of screening colonoscopy on the life expectancy of older and younger patients, researchers conducted a study among patients in three age groups: 50-54, 75-79, and 80 or older. All patients underwent screening colonoscopy. None of the patients experienced complications from the procedure.

  • Colorectal polyps were detected more frequently in older patients: polyps were detected by colonoscopy in 14% of patients between the ages of 50 and 54, 27% of patients between the ages of 75 and 79, and 29% of patients age 80 or older.
  • In spite of the more frequent detection of polyps in older patients, the increase in life expectancy that resulted from colonoscopy was smaller for older patients than for younger patients. Among patients between the ages of 50 and 54, the average gain in life expectancy that resulted from screening colonoscopy was roughly 10 months. In contrast, among patients aged 80 or older, the average gain in life expectancy was roughly one-and-a-half months.

The researchers conclude, “Screening colonoscopy in very elderly patients should be performed only after careful consideration of the potential benefits, risks, and patient preferences.”

Patient Time Requirements for Screening Colonoscopy Defined

According to an early online article published by the American Journal of Gastroeneterology, time requirements of a patient for undergoing screening colonoscopy have been defined. It is important that patients understand this time commitment prior to scheduling a colonoscopy.

Colorectal cancer is the second leading cause of cancer-related deaths in the United States. Screening tests for colorectal cancer include a fecal occult blood test, sigmoidoscopy, colonoscopy, barium enema, and digital rectal exam. Colonoscopy beginning at age 50 and performed every 5–10 years, accompanied by twice annual testing for fecal occult blood, is likely the most effective way to detect early colon caner.

Unfortunately, patient compliance with conventional colonoscopy screening and fecal blood testing remains low; less than 10% of individuals over the age of 50 years undergo screening colonoscopy. Reasons for resistance to colonoscopy include the required use of sedation, the small risk of perforation of the large intestine, and the invasive nature of the test. In addition, a screening colonoscopy requires a significant time commitment. It is important for individuals to understand this commitment before scheduling a screening colonoscopy.

Researchers from the University of North Carolina recently conducted a study to determine the time requirements for performing screening colonoscopy. The following observations were made in 110 individuals undergoing screening colonoscopy:

  • GI cleansing preparation time: 16.5 hours
  • Travel time: 1.1 hours
  • Waiting time: 1.4 hours
  • Time for sedation: 12 minutes
  • Time for colonoscopy: 20 minutes
  • Onsite recovery time: 47 minutes
  • Time in endoscopy center: 2.8 hours
  • Time from completion of endoscopy until return to normal activities: 17.7 hours
  • Time from completion of endoscopy until feeling completely normal: 19.9 hours

The authors stated that time requirements were affected by history of depression, type of person accompanying the patient, income, and employment status. Individuals who are to undergo a colonoscopy may wish keep these time commitments in mind when scheduling their procedure.


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  2. Imperiale T, Glowinski E, Lin-Cooper C, et al. Five-year risk of colorectal neoplasia after negative screening colonoscopy. New EnglandJournal of Medicine. 2008;359:1218-1224.
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