Colonoscopy is the technique of choice for evaluation of patients with positive fecal occult blood (FIT). Identification of polyps and their removal has been shown to decrease colorectal cancer incidence rates and mortality. Many endoscopic imaging technologies and devices have been developed to increase adenoma detection (ADR) during screening colonoscopies. They vary in the way they work, and some of the technologies are costly and not widely available. Studies has shown the simple to use pan-colonic chromoendoscopy can improve ADR compared to standard colonoscopy. However, there is little evidence on the utility of pan-colonic chromoendoscopy in asymptomatic individuals undergoing colonoscopy after a positive FIT test. In this randomized study, the investigators aim to compare the utility of chromoendoscopy and high-definition white-light endoscopy in asymptomatic individuals undergoing colonoscopy after a positive FIT test

Eligible subjects with positive screening FIT test referred to the Department of Gastroenterology, Singapore General Hospital will be approached and recruited. The included patients will be randomised to either a) Group A- Chromoendoscopy or b) Group B- high definition white light based evaluation.

Hypothesis:

The investigators hypothesize that application of non-absorbable dye during colonoscopy would enhance the mucosal contrast, delineate the border and surface patterns by accumulating in the innominate grooves and, thereby, enhance the detection of adenoma during colonoscopy

Procedure:

Pan-colonic chromoendoscopy and high-definition white light endoscopy will be performed by five experienced endoscopist, and hospital sedation guidelines will be followed. The colonoscopy will be performed using Olympus (CF-HQ190) or Fujifilm (EC-590) colonoscopies. Indigo carmine dye will be used for pan-colonic chromoendoscopy. Two ampules of Indigo carmine (0.8%, 5ml/ampule) will be dissolved in 250 ml of water and sprayed through the waterjet channel by using the auxiliary foot pump upon reaching the caecum.

The colonoscopy insertion will be performed using high-definition white light, and the scope will be advanced till the caecum. The quality of the bowel preparation will be rated according to the validated Boston bowel preparation score. Participants with inadequate bowel preparation score (Score <6) will be excluded from the study. The fecal residue will be washed, suctioned and cleared during insertion to improve visibility. No special care will be taken to look for lesions during the insertion. Assessment for colonic lesions will only be performed during withdrawal of the endoscope. The minimum withdrawal time was set at 7 minutes. Randomization: Once the caecum is intubated and if the bowel preparation is adequate, the participants will be randomized to pan-colonic chromoendoscopy based withdrawal or high-definition while light based withdrawal. In the pan-colonic chromoendoscopy group, the indigo carmine was sprayed by pressing the auxiliary foot pump, and dye was delivered systematically to coat the entire colonic mucosa. In both, the groups, the lesion size, number, location, morphology will be documented during withdrawal. The investigators characterized the morphology of the lesion according to the established Paris classification. The investigators characterized the lesion as flat neoplasm if the lesion project <2.5mm or polypoid lesion if lesion project >2.5mm into the lumen. The investigators measured the size of the lesions using an open biopsy forceps when needed.

In both the groups, the identified polyps will be removed using the standard techniques, and the tissue will be placed in separate formalin bottles and sent for histology assessment. The histology of the polyps was assessed by dedicated pathologist trained in gastrointestinal pathology. Both the endoscopists and the pathologist will not be blinded to the study technique. The investigators defined advanced adenoma as any adenoma >10 mm in size or with >25% villous histology or high-grade dysplasia. The investigators classified hyperplastic polyps and sessile serrated polyps (SSA) as serrated lesions, The investigators excluded hyperplastic lesions in the rectum from the analysis as such lesions are frequently encountered in the rectum

Inclusion Criteria:

• Age older than 50 years
• Positive stool FIT test or FOBT test

Exclusion Criteria:

• Known inflammatory bowel disease
• Known polyposis syndromes
• Previous history of colon cancer and surgical resection
• Overt gastrointestinal bleeding
• Stool FIT or FOBT test performed during hospitalization
• Inadequate bowel preparation (Boston Bowel Preparation score <6 or <2 for each colonic segment)
• Poor patient tolerance to the procedure
• Pregnancy
• Concurrent intake of anticoagulants and thienopyridines (e.g., Clopidogrel), where these drugs cannot be suspended for the adequate duration before colonoscopy
• Patient with known history of hypersensitivity to Indigo carmine dye