The hypothesis to be tested is that position changes during the withdrawal phase of colonoscopy leads to a higher adenoma (polyp) detection rate because of better distension of the colon. Since adenomas are precancerous lesions the enhanced adenoma detection will increase the success of colorectal cancer screening programmes. This study will provide evidence for the value of position changes and encourage endoscopist to adopt position change as a routine in their practice. May 2007: protocol amendment to include additional prospective analysis using High Definition TV (HDTV).

Colorectal cancer is the second commonest cause of cancer death. In a majority of cases it is preceded by a precancerous lesion called an adenoma (commonly known as polyp). Detection and removal of adenomas at colonoscopy has been shown to reduce mortality from colorectal cancer. The success of the impending colorectal cancer screening programme to reduce cancer mortality in an average-risk population depends on optimal adenoma detection at colonoscopy. The detection of adenomas has been shown to vary between different endoscopist. Some of the factors that have been reported to affect adenoma detection rates included the time spent viewing, the adequacy of the bowel preparation and the time spent cleaning the colonic mucosa of excess fluid. Careful examination of proximal side of flexures, folds and valves by the endoscopist is equally important. However, even with careful examination adenoma detection rates have been shown to vary between endoscopist from 8.6% to 15.9%. Previous experience and training may be contributed to this difference. Some endoscopist adopt regular changes in position during the procedure to maximize distension of the colon. Better luminal distension enhances mucosal views for detection of the smaller adenomas. The validity of this approach has never been tested and we propose that this factor may contribute to the differences in adenoma detection rates. Patients will be randomised to either position 1 first then position 2 or vice versa and examined twice. During one withdrawal the colon will be examined with the participant in the left lateral position only (position 1) or with position changes (position 2)or vice versa.

May 2007: protocol amendment to include additional prospective analysis using High Definition TV (HDTV). No further patient data collection involved.

Inclusion Criteria:

• Patients referred ot colonoscopy, age between 50 - 70 years

Exclusion Criteria:

• Patients with colorectal cancer, previous colonic surgery, active colitis and musculoskeletal problems Patients may also be excluded after the first insertion, if painful, routine care will proceed