Bowel Preparation for Colorectal Cancer Screening: Improving Outcomes

This article originally appeared here.
Share this content:
Stool burden can be a particularly challenging aspect of colonoscopies, making potentially cancerous lesions easier to miss.
Stool burden can be a particularly challenging aspect of colonoscopies, making potentially cancerous lesions easier to miss.

Colonoscopy is one of the primary screening modalities for colorectal cancer (CRC). During this procedure, the colonic mucosa can be directly visualized, and precancerous lesions such as tubular adenomas can be removed. Although colonoscopy is not considered a surgical procedure, it is still somewhat invasive and requires a bowel preparation in order to allow for complete visualization of the mucosa and identification of polyps. The bowel preparation is considered by patients as one of the most challenging components of the colonoscopy. Therefore, attention to detail with respect to the bowel preparation is crucial to improving adequate CRC screening.

Close to 25% of bowel preparations are considered inadequate during colonoscopy.1,2,3 An “inadequate” prep had previously been documented using a more subjective, operator-dependent evaluation of the bowel, including terms such as “fair” and “poor”. This can lead to significant variability when interpreting colonoscopy results. In general terms, an inadequate prep may be defined by the presence of excess solid or semi-solid stool that could not be completely irrigated and suctioned, therefore, certain lesions such as polyps or cancers may have been missed. This type of stool burden can be particularly challenging, potentially making lesions easier to miss.

To remove some of the subjectivity associated with the nomenclature of bowel preparation, some standardized measures of evaluation utilize more objective scales. These scales include the Aronchick Bowel Preparation Scale, Ottawa Bowel Preparation Scale, and Boston Bowel Preparation Scale (BBPS).4 For example, the BBPS uses a scoring system of between 0 and 3 to evaluate the 3 parts of the colon: right, transverse, and left.5 Each part of the colon receives a numerical value and then these values are combined for a final score. A score of 6 or higher was considered adequate, while scores of less than 6 where deemed inadequate. The BBPS has been validated in clinical trials; a higher score generally leads to better polyp detection rates.5 Therefore, when reviewing a patient's CRC screening and colonoscopy history, it is important to evaluate how the prep was described and if it was defined an objective system.

Inadequate bowel preparations can lead to increased risk of adverse events in the patient, as well as decreased rates of detection for adenoma.6 A previously inadequate bowel preparation is the most important risk factor for an inadequate preparation in the future, so this is a key question to ask patients. Additional risk factors include patients of the male sex, a history of opioid use, a history of constipation, the presence of certain medical conditions (diabetes mellitus, cirrhosis, obesity, Parkinson disease), and poor health literacy.7

There are 2 primary protocols for the administration of a bowel preparation: single dose and split dose. In the single-dose prep, the patient takes the entire volume (typically 2 to 4 liters) either the night before the procedure or the day of the procedure (for colonoscopies occurring in the afternoon). In the split-dose prep, half of the prep is given the evening before the procedure, followed by the second half given approximately 5 hours before the procedure. It is important to complete the second half of the prep no later than 2 hours before the procedure to avoid potential delays in receiving anesthesia.4

Split dosing has become the preferred modality for bowel prep based on multiple studies. In a meta-analysis conducted by Bucci and colleagues, a good or excellent preparation was found in 85% of patients (95% confidence interval [CI], 0.82-0.88) using split dosing compared with 63% of those who did not receive a split dose (95% CI 0.55-0.71).8 These findings were also seen in a subgroup analysis based on the different types of prep formulation (eg, high vs low volume), with split dosing having better rates of adequate prep by between 15% to 30%. In a separate study, split dosing was also shown to increase both the adenoma detection rate and polyp detection rate following the implementation of a split-dosing protocol.9 Split dosing increased the polyp detection rate from 44.1% to 49.5% (P < .001), increased the adenoma detection rate from 26.7% to 31.8% (P < .001) and increased the observed percentage of patients with at least 1 adenoma that was 10 mm or greater from 6.7% to 8.2% (P = .04).

There are several potential strategies to implement if a patient has had an inadequate prep previously or is at increased risk of inadequate prep. As mentioned previously, split-dosing regimens have better outcomes. At-risk patients should receive more extensive counseling and educational materials. A thorough medication reconciliation should be completed beforehand to see if there are medication options that could serve to limit certain medications known to promote constipation. The prep may be better tolerated by patients if it is chilled prior to ingestion, if flavor packets are used, and if it is sipped through a straw. Some patients may require a diet of 2 days of a clear liquid to prepare the bowel, especially if those patients have a history of constipation. Lower volume preps may also be easier to tolerate.


  1. Harewood GC, Sharma VK, de Garmo P. Impact of colonoscopy preparation quality on detection of suspected colonic neoplasia. Gastrointest Endosc. 2003;58(1):76-79.
  2. Froehlich F, Wietlisbach V, Gonvers JJ, Burnand B, Vader JP. Impact of colonic cleansing on quality and diagnostic yield of colonoscopy: the European panel of appropriateness of gastrointestinal endoscopy European multicenter study. Gastrointest Endosc. 2005;61(3):378-384.
  3. Ness RM, Manam R, Hoen H, Chalasani N. Predictors of inadequate bowel preparation for colonoscopy. Am J Gastroenterol. 2001;96(6):1797-1802.
  4. The ASGE Standards of Practice Committee, et al. Bowel preparation before colonoscopy. Gastrointest Endosc. 2015;81(4):781-794.
  5. Lai EJ, Calderwood AH, Doros G, Fix OK, Jacobson BC. The Boston bowel preparation scale: a valid and reliable instrument for colonoscopy-oriented research. Gastrointest Endosc. 2009 Mar;69(3 Pt 2):620-625.
  6. Chokshi RV, Hovis CE, Hollander T, Early DS, Wang JS. Prevalence of missed adenomas in patients with inadequate bowel preparation on screening colonoscopy. Gastrointest Endosc. 2012;75(6):1197-1203.
  7. Hassan C, Fuccio L, Bruno M, et al. A predictive model identifies patients most likely to have inadequate bowel preparation for colonoscopy. Clin Gastroenterol Hepatol. 2012;10(5):501-506.
  8. Bucci C, Rotondano G, Hassan C, et al. Optimal bowel cleansing for colonoscopy: split the dose! A series of meta-analyses of controlled studies. Gastrointest Endosc. 2014;80(4):566-576.
  9. Gurudu SR, Ramirez FC, Harrison ME, Leighton JA, Crowell MD. Increased adenoma detection rate with system-wide implementation of a split-dose preparation for colonoscopy. Gastrointest Endosc. 2012;76(3):603-608.
You must be a registered member of Clinical Advisor to post a comment.

Sign Up for Free e-newsletters