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Methods
Study Design
This is a retrospective database study supplemented by chart review from the Ann Arbor Veterans Affairs Health Care System (VAHCS) in-hospital endoscopy suite, the University of Michigan in-hospital medical procedure unit, and two University of Michigan out-patient ambulatory surgery centers (Livonia, MI and Ann Arbor, MI). Medical records of consecutive average-risk patients ≥50 years old undergoing colonoscopy for CRC screening between 1 January 2009 and 31 December 2009 were reviewed. These dates preceded institution of PM/AM split-dose bowel preparation protocols in 2010, and hence these data reflect outcomes with PM-only bowel preparation protocols. Inclusion criteria were average-risk outpatients referred for CRC screening colonoscopy without any polyps identified during colonoscopy. Subjects were excluded for: concurrent gastrointestinal (GI) symptoms (i.e., one of the indications for colonoscopy was listed as anemia, overt or obscure GI blood loss, abdominal pain, diarrhea, unexplained weight loss, and so on); family history of CRC; personal history of CRC, colon polyps, hereditary CRC syndrome, inflammatory bowel disease; detection of any colon polyps during colonoscopy, detection of mucosal abnormalities during colonoscopy that required biopsy, or incomplete colonoscopies (i.e., failure to visualize the appendiceal orifice and cecum). Patients with follow-up recommendations for "Barium Enema" or "Discontinue due to age" were also excluded. Institutional Review Board approval was obtained at the Ann Arbor VAHCS and University of Michigan before study initiation.
Protocol for Bowel Preparation and Definition of Bowel Preparation Quality
If the laxative was polyethylene glycol, HalfLytely, MoviPrep, NuLYTELY, or TriLyte, the patients were instructed to follow the Food and Drug Administration (FDA)-approved instructions for consuming the bowel preparation using a PM-only protocol. For MiraLAX/Gatorade, patients took two tablets of bisacodyl between 12 PM and 6 PM and followed 4 h later by consumption of 238 g of MiraLAX mixed in 64 oz of Gatorade.
Bowel preparation quality and other endoscopic data were reported via the ProVation Medical Systems v.42 and v5.0 (Wolters Kluwer Health, Minneapolis, MN) at the Ann Arbor VAHCS and University of Michigan endoscopy sites, respectively, using the Aronchick scale that categorizes bowel cleansing as follows: excellent: >95% of mucosa visualized; good: 90–95% of mucosa visualized, fair: 80–90% of mucosa visualized, and poor: <80% mucosal visualization. We collapsed excellent and good categories for simplicity because the clinical importance of 90–95 vs. >95% visualization of the mucosa is unclear.
Endoscopist Recommendation Intervals
Data on the endoscopists' recommendation for follow-up screening colonoscopy were abstracted from patient colonoscopy report forms. Recommendations consistent with guidelines were defined as follow-up in 10 years for excellent, good, or fair bowel cleansing or ≤1 year if bowel preparation quality was rated poor. Although guidelines published in 2009 or earlier do not specifically recommend the appropriate interval for repeat colonoscopy after poor bowel preparation, they do state that follow-up colonoscopy should be scheduled at a "prompt," "a relatively short interval", and "within 6 months". We believe this common-sense approach was understood by the vast majority of endoscopists practicing in 2009 and that they would not consider it appropriate to recommend repeat screening colonoscopy at intervals >1 year after poor bowel preparation in an average-risk patient referred for CRC screening with colonoscopy. In fact, the 2012 multisociety guidelines now specifically recommend repeat colonoscopy in ≤1 year after poor bowel preparation. Failure to provide a recommendation for repeat screening colonoscopy was also considered inconsistent with guideline recommendations as endoscopists are required to make this recommendation as part of reporting in PQRS.
Subject and Procedure Data
Data were collected on age, gender, body mass index, race/ethnicity, concurrent narcotics and tricyclic antidepressant usage, presence/absence of diabetes, type of bowel preparation agent used, whether a GI fellow participated, endoscopists' categorization of procedural difficulty, and cecal intubation. Specific endoscopist characteristics were not collected because of privacy issues raised by our institutional review board that stated that all endoscopists would need to provide informed consent even if they no longer practiced at the University of Michigan as collection of these data might be used to retrospectively assess these endoscopists.
Statistical Analysis
Bowel preparation quality was categorized as excellent/good, fair, or poor. Recommendation appropriateness was a dichotomous variable: consistent with guideline recommendations vs. inconsistent with guideline recommendations. The χ tests and Student's t-tests were used to assess study population differences based on bowel preparation quality and based on whether or not their recommendation was consistent with guidelines. A saturated multivariate logistic regression model was used to determine independent predictors of receiving a recommendation inconsistent with guidelines. Database management and statistical analysis was performed using SAS 9.2 (SAS Institute, Cary, NC).
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