Incidence of colorectal cancer (CRC) has increased in the world (8.2 per 100,000 in year 2008 vs. 17.2 per 100,000 in year 2012) [1,2].Interestingly, there is sex difference of CRC in terms of incidence (10.0 per 100,000 in males vs. 9.2 per 100,000 in females) and mortality (8.0 per 100,000 in males vs. 9.0 per 100,000 in females). In Korea, the incidence of CRC has rapidly increased; CRC became the second most common cancer (52.6 per 100,000). CRC was the sixth most common cancer (16.3 per 100,000) among cancers that caused mortality [3]. Similar to other countries, there is also sex difference of CRC in term of incidence (62.5 per 100,000 in males vs. 42.7 per 100,000 in females) and mortality (18.5 per 100,000 in males vs. 14.1 per 100,000 in females) in Korea [4,5]. Male is a risk factor of CRC. CRC also develops earlier in males than in females. Thus the screening protocol of CRC should be different between males and females [4,5]. However, CRC screening guidelines do not distinguish males and females. CRC developed from proximal (right-sided) or distal (left-sided) colon shows differences in incidence according to geographic region, age and sex [6,7]. It is known that patients with proximal colon cancer are older and having more females than those with distal colon cancer. In addition, there is a difference in cancer morphology. That is, proximal colon cancer is more often flat while distal colon cancer has a polypoid-type which can be more easily detected by colonoscopy [8]. Tumor location and prognosis of CRC are also different between males and females. However, studies that consider sex specific design and interpretation of CRC are insufficient.

Colonoscopy is important for screening and diagnosis of CRC [5]. As inadequate bowel preparation affects the effectiveness and accuracy of colonoscopy examination. Thus, bowel preparation and colonoscopy quality management are important [9,10]. Several studies have reported that age, sex, physical activity, and disease are associated with bowel preparation [11-13]. The length of colon is known to be longer in females than in males [14,15]. However, there has been no research on each factor so far. In addition, previous studies have not identified other colonoscopy quality factors including cecal intubation rate, insertion time, and polyp detection rate together [11-13]. We hypothesize that there are sex differences in colonoscopy preparation quality, cecal intubation time, and withdrawal time (from point of cecal intubation to final withdrawal). If there is difference in colonoscopy quality between sexes, CRC screening guidelines which do not distinguish females from males should be revised to improve the high mortality and poor prognosis of female CRC patients [1-4]. With this background, the aim of this study was to determine sex difference of colonoscopy quality in terms of bowel preparation, insertion time, withdrawal time, and polyp detection rate.

Recently, there has been a growing interest in sex specific difference. Some studies have reported health difference between males and females [14,15,24]. Sex and gender differences show diverse physiological and psychological factors. Sex hormones and gender differences might play important roles in disease development and progression [24]. For instance, Menon et al. [25] have suggested that sex hormones can directly affect bacterial metabolism, bacterial growth, and gene expression of virulence factors through steroid nuclear receptor expression including estrogen receptor β.In addition, Kim et al. [26] have demonstrated that reflux symptoms affect female patients with gastroesophageal reflux disease more than in male ones, and quality of life was also more impaired in females.In terms of cancer, Kotake et al. [27] have shown that reduced risk of cancer-specific death for women relative to men persists over time. Zheng et al. [28] have shown that sex hormones play a crucial role in the pathogenesis and development of hepatitis B virus-induced hepatocellular carcinoma. Males with private insurance undertook colonoscopy more frequently [29]. However, employed males were less likely to eat salty food, be older, and smoke [29]. Diagnostic interval was longer for females than for males in CRC (mean difference; 10.4 days; 95% confidence interval, 4.3 to 16.5; p = 0.001) [30].

There have been some reports regarding sex difference in colonoscopy quality [13,31-33]. Ness et al. [13] have suggested that male sex (odds ratio, 0.85) is associated with inadequate bowel preparation. Similarly, Rotondano et al. [31] have examined factors associated with quality of bowel cleansing and found that men gender is a predictor of inadequate cleansing at right colon and left colon (p = 0.040 and p = 0.014, respectively). In addition, Akere and Otegbayo [32] have examined 167 patients to find factors affecting cecal intubation time. They found that men are associated with prolonged cecal intubation time (913.86 ± 453.28 seconds in males vs. 910.44 ± 513.33 seconds in females, p = 0.443). In contrast, males showed higher success rate of cecal intubation within 20 minutes than females (83.9% in males vs. 77.6% in females, p = 0.004) [33]. However, there is a lack of research that conclusively proves the sex difference in colonoscopy quality. In addition, previous studies have limitation such as small sample size [31] and insufficient variables [31,32].In addition, there has been no research analyzing colonoscopy quality between males and females like the present study. Furthermore they only statistically analyzed sex as one factor for multivariance [13,31-33].There are various colonoscopy quality indicators including colonoscopy surveillance, cecal intubation rate, adenoma detection rate (≥ 25% in males and ≥ 15% in females), colonoscopy withdrawal time (average ≥ 6 minutes) and quality of colon preparation [34]. However, few studies have been performed with a comprehensive approach in terms of sex specific manners.

In the present study, we investigated sex difference in colonoscopy quality in many aspects using a big administrative database. Colonoscopy quality indicators including adenoma detection rate, colonoscopy withdrawal time, and quality of colon preparation are important to detect colon polyp and CRC in early stages [34]. However, there has been no study about sex difference in these indicators. Males and females have different incidence and mortality of CRC. Our results suggest that sex difference of colonoscopy quality indicator might be associated with early detection and mortality of CRC.

Clearly, sex difference was identified in bowel preparation. We analyzed various guidelines for adequate bowel preparation and found that females showed better bowel preparation results. It is known that bowel preparation is influenced by various factors [11-13,35,36]. Our study showed that sex factor could influence bowel preparation based on a large cohort database. Our results suggest that we should more carefully educate male patients who receive colonoscopy for adequate bowel preparation. Whether sex difference of bowel preparation is associated with chromosome or genetic difference merits further study.

Our study showed sex difference in cecal intubation time and withdrawal time. Sex difference of cecal intubation time might be associated with anatomical difference between males and females [14,15]. Thus, we need to schedule female patients with enough colonoscopy time. Sex difference of withdrawal time might be associated with polyp detection rate. Male showed higher polyp detection rate. Therefore, withdrawal time in males might need to be longer than in females.

Our study showed that polyp detection rate was different between males and females. It might be associated with the higher incidence of CRC in males [1-3]. Thus, careful colonoscopy inspection is needed for males. These results suggest that different indication of colonoscopy and colonoscopy follow-up interval might be needed based on sex difference of bowel preparation method and colonoscopy withdrawal time. More studies are needed to determine the appropriate colonoscopy follow-up term for males.

We analyzed sex difference of bowel preparation with bowel preparation drugs Coolprep and Picosolution widely used in Korea. Some studies have reported that these two drugs have no significant adverse effects with similar bowel of cleansing [37-40]. In the present study, females showed better total BBPS score, adequate bowel preparation (BBPS ≥ 6), and recent adequate bowel preparation (BBPS ≥ 2 for all segments) in Coolprep. However, there was no sex difference in cases of Picosolution in contrast to Coolprep. We cautiously believe that the reason might be because subjectsneedes to drink 2 L of Coolprep with mixed solution from the beginning. Thus, males might not have followed the instruction more precisely than females. Our results suggest that bowel preparation might be different depending on which bowel preparation drugs are taken. Thus, male patients should be educated how to clean bowel more carefully. In addition, it is necessary to study how to clean the bowel in males. Whether different bowel preparation drugs show different effectiveness remains controversial. Previous reports have suggested that bowel preparation is associated with not only drugs, but also drug compliance and fiber diet education [35,36]. Our study showed that there was a sex difference in bowel preparation status using bowel preparation drugs. Thus, when Coolprep or Picosolution was planned, this result should be carefully considered. In addition, there was a difference in size between Coolprep and Picosolution groups. Therefore, more studies are needed.

We thought that analysis of colonoscopy by experienced colonoscopists was our study’s strength. The skill and career of colonoscopist depending on training period can affect cecal intubation time and polyp detection rate. Our study eliminated the selection bias due to exclusion of colonoscopy cases by colonoscopists with experience of less than 5 years.

However, our study has some limitations. First, this study was performed in one institute due to the Personal Information Protection Acting Korea. However, there was an advantage of research because description format was made before this study. Thus a consistent approach was possible and description was well educated with the figure to avoid selection bias. Second, we analyzed colonoscopy information according to electronic medical records for a large number of cases. However, we could not verify other factors such as patient’s compliance and history of colonoscopy. In addition, our study could not deal with analysis of pathologic result. We thought that analysis of pathologic findings including grade of adenoma and carcinoma should be needed.

In conclusion, there was a sex difference in colonoscopy indicator. Males showed less clean bowel preparation. However, polyp detection rate in males was higher than that in females. Thus, males should be educated regarding how to perform bowel preparation carefully. Colonoscopists need to reserve relatively more time of colonoscopy for females. Whether the sex difference of various colonoscopy indicators is associated with chromosome or genetic difference merits further study.