Colonoscopy with suboptimal bowel preparation after a positive fecal immunochemical test: what lies beneath?

The last two decades have seen a burgeoning of programs to systematically screen for colorectal cancer [1]. Along with colonoscopy, the use of the fecal immunochemical test (FIT) has emerged as a primary means for achieving large-scale, population-based screening [2] and is endorsed by many professional societies [2] [3]. Individuals who screen positive with a FIT are referred for colonoscopy for the removal of adenomas or to confirm and locate colon cancer. Because the positive predictive value of a FIT ranges from 34 % to 54 % [3], many of the colonoscopies performed for a positive FIT will fail to discover neoplasia. Nonetheless, a high quality colonoscopy, with adequate bowel preparation, should be performed for any individual with a positive FIT. In the setting of suboptimal bowel preparation, meaning preparation that some endoscopists might consider borderline and not inadequate, what is the likelihood that one is missing an adenoma or malignancy? And should we still make a distinction between suboptimal and inadequate bowel preparation?

To address the first question, Baile-Maxía and colleagues performed a retrospective, cross-sectional study of 2474 patients aged 50 – 69 years who underwent colonoscopy after a positive FIT [4]. Testing was part of an organized screening program in the Valencian Community in Spain. The investigators used the Boston Bowel Preparation Scale (BBPS) [5] to distinguish between inadequate preparation (≥ 1 segment scoring 0), which required immediate rescheduling and was excluded from the analysis, and suboptimal preparation (≥ 1 segment scoring 1) although the cecum was reached. In this latter situation, the authors sought to determine the adenoma detection rate (ADR) and advanced ADR (AADR; ≥ 10 mm, high grade dysplasia, or villous architecture) during repeat colonoscopy performed within 18 months. The remainder of the cohort had BBPS scores ≥ 2 for all their segment and were therefore excluded.

“When encountering suboptimal preparation in a FIT-positive patient, endoscopists should expend every effort to achieve an adequate degree of preparation during the colonoscopy itself.”

Because endoscopists were expected to have removed all visible adenomas during the index colonoscopy, the authors also determined the per-adenoma miss rate by dividing the number of adenomas at repeat colonoscopy by the total number found during the index and repeat procedures. After exclusion for inadequate bowel preparation at either the index or repeat colonoscopy (n = 17), lack of cecal intubation or missing colonic segment (n = 22), and loss to follow up (n = 55), 248 subjects remained for analysis. The mean period between the index colonoscopy and the repeat colonoscopy was 352 days.

The primary finding was that subjects with suboptimal preparation had a large number of lesions found during repeat colonoscopy, with an ADR and AADR of 39 % and 15 %, respectively. There were no missed cancers. Of note, the ADR and AADR for the entire cohort at the index colonoscopy was 65 % and 48 %, consistent with the published literature, and comfortably exceeding the suggested minimums in the setting of a FIT with a cutoff value of 20 μg/g of feces, as used in this study [3]. Other important findings included per-adenoma and per-advanced adenoma miss rates of 28 % and 18 %, respectively, and that 17 patients among the 248 (7 %) had a change in their recommended surveillance interval from 10 years to 3 years, based on the finding of adenomas at the repeat colonoscopy. Baile-Maxía and colleagues therefore provide further evidence that a BBPS segment score < 2 defines inadequate bowel preparation that should prompt another attempt at colonoscopy [5] [6].

There are additional important lessons to take away from this study. First, the overall bowel preparation adequacy rate was 87 %, which is lower than the current 90 % target set by the European Society of Gastrointestinal Endoscopy (ESGE) [7]. As the authors explained, their low rate occurred prior to the adoption of split-dosing bowel purgatives as their standard preparation. However, we should also consider the degree of effort made by endoscopists to perform additional washing and clearing of debris during colonoscopy. When a preparation is truly poor, endoscopists likely abort the procedure and reschedule the patient, perhaps with additional emphasis on, or alteration of, the preparation regimen. But what about the situation where the endoscopist is faced with a potentially salvageable preparation quality, particularly if the indication is a positive FIT? Perhaps endoscopists should be devoting additional effort during the index colonoscopy to ensuring that adequate preparation is ultimately achieved. If not already done, endoscopy units should strive to equip each room with a water pump to facilitate cleansing.

The need to maximize the adequacy of bowel preparation during the initial procedure was also highlighted in this study by the fact that 55 of 314 patients (18 %) with suboptimal preparation failed to return for a repeat colonoscopy within 18 months, despite their positive FIT. Given the high likelihood that such patients harbor at least one missed adenoma, this sobering loss to follow-up should serve as motivation for endoscopists to try everything they can to achieve adequate preparation on the first occasion.

Second, the findings suggest we should not distinguish between suboptimal and inadequate bowel preparation, particularly in the setting of a positive FIT. Both terms indicate a high likelihood of missed neoplasia, even if the cecum is reached, and should prompt the same response; namely rescheduling a timely repeat colonoscopy. Finally, there is an important caveat for medical providers using the FIT as the first-line screening procedure for patients they deem unlikely to achieve adequate preparation (e. g. chronic constipation or immobility). Should the FIT return positive, these hard-to-prep patients must now somehow achieve adequate bowel cleansing. This highlights the need for further research into novel purgatives and technologies for clearing the colon of debris [8].

In summary, Baile-Maxía and colleagues provide very strong evidence that colonoscopy with adequate bowel preparation is the only acceptable option for patients with a positive FIT. Every effort must be made to ensure patients with a positive FIT are well-educated about, and supported through, the bowel preparation process. When encountering suboptimal preparation in this setting, endoscopists should expend every effort to achieve an adequate degree of preparation during the colonoscopy itself. When the preparation is truly inadequate despite their best efforts to perform intraprocedural cleansing, there must be a rigorous system in place to ensure patients return in a timely manner and with preparation that permits complete inspection of the colonic mucosa.

Publication History

Article published online:
25 November 2020

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