Colonoscopy is the most important tool for the diagnosis and treatment of colonic diseases [16, 17]. Inadequate bowel preparation not only affects the accuracy of colonoscopy, but also has a detrimental effect on other aspects of the colonoscopy, including cecal intubation failure, need for repeated procedures, longer hospital stays, and increased healthcare costs [18–20]. Therefore, determining the risk factors for poor colon preparation would help in providing more intensive bowel preparation to the subjects.
Two recent meta-analyses by Gandhi K et al and Mahmood S et al, involving 67 and 24 studies, respectively [12, 21], identified that patients’ baseline characteristics (elderly age and male), clinical conditions (constipation, diabetes mellitus, hypertension, cirrhosis, stroke, and dementia), and medication use (narcotics and tricyclic antidepressants) were the risk factors of poor bowel preparation. Additionally, we observed that patients in different seasons had different quality of colon preparation. However, whether season is the independent risk factor of bowel preparation was still unknown. To our knowledge, this is the first study to report the relationship between season and bowel preparation. Choosing different plans for different seasons can effectively improve the proportion of patients with adequate bowel preparation.
Diet restriction is also known to be a risk factor for bowel preparation [22]. Many studies had shown that clear liquid diet (fruit juices, sports drinks, etc.), a lower residue or fiber diet would have higher proportions of patients with adequate bowel preparation [23–25]. Moreover, patients with a lower residue or fiber diet would be more willing to repeat the procedure and had better tolerability [26]. Besides, Liu X et al found telephonic re-education on the day before colonoscopy could improve the quality of bowel preparation [13]. Hence, in the present study, patients were advised to have a lower residue or fiber diet before colonoscopy, and all patients received telephone-based re-education on the day before colonoscopy.
In the present study, male was found to be an independent risk factor for poor bowel preparation (OR: 1.295; 95% CI: 1.088–1.542; P = 0.005). It may be due to the difference in the working environment and living habits of men and women, and also because male patients may be less compliant with the instructions for bowel preparation [27]. Age ≥ 50 years was associated with inadequate bowel preparation on univariate analysis (OR: 1.19; 95% CI: 1.004–1.417; P = 0.045). Previous study indicated that decreased tolerance and slow gastrointestinal motility could contribute towards poor bowel preparation in the elderly population [21]. However, in this study, age ≥ 50 years was not an independent risk factor on multivariate analysis (P = 0.124). In the current study, we also found inpatients had a worse colon preparation (OR: 1.377; 95% CI: 1.040–1.822; P = 0.025). Previous studies have also found that a high proportion of hospitalized patients undergoing colonoscopy had inadequate bowel preparation [28]. This may due to the proportion of inpatients with other diseases, which are risk factors for bowel preparation, was higher. Besides, hospitalized patients are less mobile compared with outpatients which may have contributed to poor bowel preparation. Therefore, inpatients should be provided with aggressive bowel preparation regimens and encouraged to increase their physical activity prior to colonoscopy.
Perhaps the most important finding we identified in this study was that the season was an independent risk factor of inadequate bowel preparation. Using winter as a reference point, patients in spring had worse bowel preparation (OR: 1.514; 95% CI: 1.139–2.012; P = 0.004), while patients in summer had better colon preparation (OR: 0.738; 95% CI: 0.546–0.948; P = 0.050). The exact season for this observation is not known. However, different seasons have different climates, and people's activities are also different. We hypothesized that it may be people’s different activitues in different season contribute to the quality of bowel preparation varied in different seasons. Summer is the hottest season. Hence, in summer, people's activities are more frequent than other seasons. Increased activities promote intestinal peristalsis and facilitate the bowel emptying [29]. In the study area, as temperatures warm in spring, the moisture on the earth evaporates into steam. Therefore, though the temperature in spring is higher than winter, people still feel colder in spring. Besides, it also rains more in spring. Hence, people’s activities in spring may be less than winter. However, the evidence is limited and further studies are needed to determine the reasons for poor bowel preparation in spring. In our study, colonoscopies in winter were obviously fewer than other seasons due to the patients’ reluctance to undergo colonoscopy in winter [30].
There are some limitations of this study. First, the present study was a single-center retrospective study. The findings of the present study need to be validated by multicenter prospective studies. Second, multiple patient-related factors such as body mass index (BMI), patients’ education and history of colon preparation, comorbidities such as diabetes mellitus, medication history were not recorded in this study. But, whether BMI and history of colon preparation affect the bowel preparation is still not clear [9, 12, 21]. However, the number of cases included in this study was large and no previous articles on season and intestinal cleanliness have been published. Hence, our research is still of clinical significance.
In conclusion, male, inpatient status and spring season were the independent risk factors for poor bowel preparation. Compared with autumn and summer, patients in spring may need intensive bowel preparation. Male patients and inpatients should receive more enhanced instructions for bowel preparation.