To determine the detection rate and distribution characteristics of colorectal adenomas in Ningbo area of China, and to identify the risk factors for colorectal adenoma, in order to provide reference for colorectal cancer screening.

A cross-sectional study was performed among 8660 subjects undergoing colonoscopy in the Ningbo No.2 Hospital between January and December 2016, using a questionnaire, including demographic data (age, gender, height and weight) , history of diseases (diabetes, hypertension, hyperlipidemia, and family history of malignant neoplasm) , lifestyle (smoking, alcohol, dietary bias on red meat, dietary bias on fruit and vegetables, dietary frequency of pickled food and physical activities) , and intestinal early warning symptoms. All colonoscopically detected polyps were removed for histological examination. Polyps were histologically divided into non-adenomatous (hyperplastic polyps and inflammatory polyps) and adenomatous polyps (tubular, villous, tubulovillous and serrated adenomas) . Pathologic features were analyzed according to anatomical site. Multivariate logistic regression analysis was used to identify the risk factors for colorectal adenoma.

A total of 7077 subjects who received colonoscopic examination and completed the questionnaire survey were enrolled in this study. There were 3633 males and 3444 females with a median age of 53 (ranged 17 to 83) years. Adenoma detection rate was 15.6% (1103/7077) in all cases, 21.0% (762/3633) for males, and 9.9% (341/3444) for females (P= 0.000) . Detection rate of 6.2% (29/469) was recorded in individuals aged less than 30 years, 8.0% (87/1086) in those from 30 to 39 years, 12.1% (148/1222) in those from 40 to 49 years, 16.8% (272/1623) in those from 50 to 59 years, 20.4% (326/1601) in those from 60 to 69 years, and 22.4% (241/1076) in those ≥ 70 years. The detection rate increased according to age (P= 0.000) . A total of 1521 adenomas were detected in 1103 cases, including 1455 tubular adenomas, 33 tubulovillous adenomas, 9 villous adenomas and 24 serrated adenomas. Among 1521 adenomas, 44.1% (n= 671) located in the right hemicolon, 39.0% (n= 593) in the left hemicolon, and 16.9% (n= 257) in the rectum. Significantly larger number of serrated adenomas and advanced adenomas (advanced adenoma was defined as any adenoma with high-grade intraepithelial neoplasia, diameter ≥ 10 mm or with villous component) was observed in the right hemicolon compared to left hemicolon and rectum [serrated adenomas: 2.5% (17/671) vs. 0.8% (5/593) and 0.8% (2/257) , P= 0.029; advanced adenoma: 9.2% (62/671) vs. 5.2% (31/953) and 6.6% (17/257) , P= 0.021]. Multivariate analysis showed that malely (P= 0.003) , elderly (P= 0.000) , obesity (P= 0.014) , smoking (P= 0.001) , alcohol (P= 0.032) , and family history of malignancy (P= 0.000) were independent risk factors of colorectal adenoma.

In view of a higher detection rate of colorectal adenoma in population aged 40 to 49 years especially in male individuals, the starting age of colonoscopy screening may be advanced to 40 years old. People with family history of malignancy, obesity, and habit of smoking or drinking should be regarded as important subjects for colonoscopy screening. During colonoscopy screening, special emphasis should be given to right hemicolon.

Colorectal adenoma; Adenoma detection rate; Colonoscopy; Risk factors; Screening