Introduction Patients with abnormal FOBt results within the Bowel Cancer Screening Programme (BCSP) are at increased risk of colorectal neoplasia and are therefore offered colonoscopy. Some patients, with significant co-morbidities, are not suitable for colonoscopy and are offered CT colonography (CTC) as an alternative. There has been concern that the insufflation tube used during this examination may obscure visualisation of low rectal lesions and this has been reported in the literature. At the West London Bowel Cancer Screening Centre all patients are offered a flexible sigmoidoscopy (FS) prior to CTC and our experience of this approach is reported in this abstract.

Methods All patients with an abnormal FOBt result, attending a Specialist Screening Practitioner (SSP) clinic between 4^th January 2012 and 1^st October 2013, and who were offered CTC and FS were identified. Their endoscopic and radiologial investigations were retrieved from the hospital electronic records system and the results recorded in terms of the adenomas and cancers identified.

Results 1544 patients were seen in an SSP clinic within the allocated period, and 73 (4.7%) of these were offered CTC. Of these 49 (67.1%) had a FS as the first investigation and 24 (32.9%) had a CTC as the first investigation. 10 (13.7%) refused FS and 14 (19.2%) had endoscopic investigations (12 FS and 2 colonoscopy) after the CTC, due to patient choice. 6 (8.2%) patients who underwent FS as the first investigation had subsequent colonoscopy without CTC, 5 as a large polyp requiring resection was found at FS and 1 following detection of a cancer. In 3 of these patients further adenomas were found at colonoscopy. In total 67 patients (91.8%) had CTC and in this group 12 (17.9%) had a subsequent colonoscopy as a result of the radiological findings. Of these 6 had a normal FS prior to CTC and 6 patients did not have a FS. In 8 cases (66.7%) the number of polyps seen on CTC was confirmed at colonoscopy, in 3 cases (25.0%) more lesions were found at colonoscopy than CTC and in 1 case (8.3%) CTC had identified more polyps than were seen at colonoscopy. 12 patients had FS after a normal CTC and no additional findings were seen on these examinations. No rectal lesions were identified at FS that were not seen at CTC. Overall 18 (24.7%) patients eventually had a colonoscopy.

Conclusion FS prior to CTC within the BCSP does not appear to be of value in detecting additional rectal lesions missed at CTC, althou gh the numbers in this analysis are small. Initial FS avoids the need for CTC in about 8% of patients, and so should be performed before CTC, but this benefit needs to balanced against the increased workload and inconvenience to patients. In those patients in whom the initial decision is to perform CTC a quarter will eventually require a colonoscopy.

Disclosure of Interest None Declared.