Colonoscopy has been demonstrated to be effective for colorectal cancer (CRC) screening and identification and removal of polyps when successfully performed. Complete visualization of the colon including the cecum is the goal of the procedure and necessary to ensure its benefits are achieved, benefits including early CRC detection and reduced patient mortality.1 Therefore, the risk of not meeting that goal—incomplete or failed colonoscopy—always is a concern for both experienced gastroenterology clinicians and fellows alike.

Incomplete colonoscopy can lead to numerous effects (eg, use of shorter surveillance intervals,2 increased cost3); however, it is the reduced adenoma detection due to incomplete colonoscopy in up to 20% of cases4 which indicates that a significant number of patients do not receive a full examination when undergoing the now common procedure.1 Double-contrast barium enema (DCBE) was once the most commonly employed tool for additional visualization in these situations,1 but capsule endoscopy (CE) and computed tomography colonography (CTC) are altering the clinician’s sequence of choices.

“In centers where there is access to a full array of alternatives, there is an opportunity to individualize strategies,” reported Seth Gross, MD, director of endoscopy at Tisch Hospital, New York University Langone Medical Center in New York City. “Selecting the best option is dependent on understanding the strengths and weaknesses of these choices in the context of patient characteristics.”

In reviewing reasons for incomplete colonoscopy, a patient-related factor, inadequate bowel preparation, often is a cause. Estimated rates of incomplete colonoscopy due to inadequate bowel preparation have been as high as 20% in some published studies.3,4

“In the past, clinicians generally held the patient accountable for an inadequate prep, but we know success rates can be improved with instruction and by individualizing regimens to improve adherence,” explained David A. Johnson, MD, chief of gastroenterology at Eastern Virginia Medical School in Norfolk, Virginia. A target for an acceptable rate of bowel prep failures is expected to be specified in coming quality metrics for colonoscopy, creating an incentive for physicians to focus on strategies to improve adherence, according to Dr. Johnson, who is a past president of the American College of Gastroenterology (ACG).

image image
An 8-mm polyp in the sigmoid colon as found by 2 visualization methods: capsule endoscopy (left) and optical colonoscopy (right).
Images courtesy of Covidien GI Solutions.

Other causes of incomplete colonoscopy such as obstructive lesions, tortuosity in the colon, or redundant colons that exceed the length of conventional endoscopes may be more challenging to manage. In some of these cases, an incomplete colonoscopy may be avoided altogether simply by transitioning to a narrow gauge or pediatric scope.5 This strategy is employed frequently by Toyia James-Stevenson, MD, assistant professor of clinical medicine in the Division of Gastroenterology/Hepatology at Indiana University School of Medicine in Indianapolis. She has combined small scopes with water immersion to achieve colon distension, increasing the likelihood of successfully navigating the scope around bends. She credits this technique with difficult examinations in patients with relative obstructions, such as those who have undergone previous pelvic surgery.

When endoscopes cannot be advanced without risk for damage to the colon, many centers are now selecting either CE or CTC, which were recently approved by the FDA for screening in patients following incomplete colonoscopy. “CTC and CE are not interchangeable. When to use one over the other is something that I think is still being sorted out, but certainly CE is a viable option that has advantages for some patients,” Dr. Johnson said. Referring to a recently published study, Dr. Johnson reported that “it is helpful that we now have comparative data.”

In the study by Spada et al, 100 patients with an incomplete colonoscopy were examined with both CTC and CE.6 Although the colon evaluation completion rate was 98% using both technologies, the rates of polyp detection significantly favored CE over CTC for polyps of at least 6 mm (24.5% vs 12.2%; Table).6 Although the detection rate for polyps of at least 10 mm (5.1% vs 3.1%) was also greater for CE, this difference did not reach statistical significance. In a mean follow-up of 20 months, there were no missed cancers.6

Table. Diagnostic Yield, Sensitivity, and Positive Predictive Valuea of CE and CTC for Polyp Detection
Polyps 6 mm Polyps 10 mm
Diagnostic yield, % 24.5 (16.6-34.4) 12.2 (6.8-20.8) 5.1 (1.9-12.1) 3.1 (0.8-9.3)
Relative sensitivity 2.0 (1.34-2.98) 1.67 (0.69-4.00)
PPV, % 96 (77.7-99.8) 85.7 (56.2-97.5) 83.3 (36.5-99.1) 100 (31.1-100)
a 95% CI.
CE, capsule endoscopy; CI, confidence interval; CTC, computed tomography colonography; PPV, positive predictive value
Adapted from reference 6.

“The comparative data are very encouraging because they suggest that CE may provide higher accuracy for polyp detection than CTC,” Dr. James-Stevenson said. “This may be related to the notion that flatter polyps may appear more prominent endoscopically when the anatomy is not distorted by insufflation.”

In patients who are candidates for either method, another advantage of CE is that it circumvents radiation exposure, which is low but remains an issue for those who have undergone repeated abdominal imaging for other reasons.1 Dr. James-Stevenson suggested that this has been a consideration at her own center, where a clinic for patients with functional bowel disease has established a pool of individuals who have undergone sufficient repeat CT scans to make a nonradiologic option attractive. Various studies have assessed other practical considerations surrounding CE and CTC use, namely patient preference and cost, and found benefits related to CE use as well.

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Capsule endoscopy showing an 11-mm polyp in the ascending colon (left); the polyp as viewed by colonoscopy (right).

In a pilot study, Imaeda et al surveyed 92 patients presenting for CRC screening on their preference of test (colonoscopy, CE, CTC, flexible sigmoidoscopy, and fecal occult blood test) and found that CE was the most preferred option (23%) outside of standard colonoscopy with positive test sensitivity ranking highest of key considerations when selecting an option.7 A more recent study among patients receiving CE following incomplete colonoscopy found that a majority (84%) would undergo the test again after experiencing mild to no adverse events.8 Additionally, studies have shown that CE and colonoscopy provide similar cost-effectiveness when compared with no CRC screening, and both tests lead to a decrease in CRC-related costs for institutions.9

Overall, CE and CTC appear to be reasonable choices for patients who are candidates for either, but Dr. Gross suggested that the comparative data have created “a crossroads” for clinicians attempting to select the option that is most suitable for the individual patient. Similarly, citing the greater sensitivity of CE, Dr. Johnson predicted that the recent Spada et al study “is likely to induce a lot of clinicians to change their practice.” Neither option is recommended first for individuals who are candidates for standard colonoscopy, but CTC is no longer the only choice for those who have an incomplete colonoscopy, and it also may no longer be the best choice given specific individual patient characteristics.

At this point, “CTC remains the most commonly used option for incomplete endoscopies, but I think it will certainly change as clinicians become aware of CE as an alternative,” Dr. Gross said.


  1. Levin B, Lieberman DA, McFarland B, et al; American Cancer Society Colorectal Cancer Advisory Group; US Multi-Society Task Force; American College of Radiology Colon Cancer Committee. Screening and surveillance for the early detection of colorectal cancer and adenomatous polyps, 2008: a joint guideline from the American Cancer Society, the US Multi-Society Task Force on Colorectal Cancer, and the American College of Radiology. Gastroenterology. 2008;134(5):1570-1595.
  2. Schreuders E, Sint Nicolaas J, de Jonge V, et al. The appropriateness of surveillance colonoscopy intervals after polypectomy. Can J Gastroenterol. 2013;27(1):33-38.
  3. Rex DK, Imperiale TF, Latinovich DR, et al. Impact of bowel preparation on efficiency and cost of colonoscopy. Am J Gastroenterol. 2002; 97(7):1696-1700.
  4. Mitchell RM, McCallion K, Gardiner KR, et al. Successful colonoscopy; completion rates and reasons for incompletion. Ulster Med J. 2002; 71(1):34-37.
  5. Jung Y, Lee S H. How do I overcome difficulties in insertion? Clin Endosc. 2012;45(3):278-281.
  6. Spada C, Hassan C, Barbaro B, et al. Colon capsule versus CT colonography in patients with incomplete colonoscopy: a prospective, comparative trial. Gut. 2014 Jun 24. [Epub ahead of print]
  7. Imaeda A, Bender D, Fraenkel L. What is most important to patients when deciding about colorectal screening? J Gen Intern Med. 2010; 25(7):688-693.
  8. Triantafyllou K, Viazis N, Tsibouris P, et al. Colon capsule endoscopy is feasible to perform after incomplete colonoscopy and guides further workup in clinical practice. Gastrointest Endosc. 2014;79(2):307-316.
  9. Hassan C, Zullo A, Winn S, et al. Cost-effectiveness of capsule endoscopy in screening for colorectal cancer. Endoscopy. 2008;40(5):414-421.

The risks of PillCam capsule endoscopy include capsule retention, aspiration and skin irritation. Endoscopic placement may present additional risks. The risks associated with colon preparation include allergies or other known contraindications to any preparation agents or medications used for the PillCam COLON regimen, according to laxative medication labeling and per physician discretion. After ingesting the PillCam capsule and until it is excreted, patients should not be near any source of powerful electromagnetic fields, such as one created by an MRI device. Medical, endoscopic or surgical intervention may be necessary to address these complications, should they occur. A normal or negative capsule endoscopy examination does not exclude the possibility of colon polyps or colon cancer. Please consult the product user manual or refer to for detailed information.