Introduction Colorectal cancer is preventable through polypectomy at colonoscopy. Most polyps are adenomas, with malignant potential, or hyperplastic with no malignant risk. Most adenomas are small (<10 mm) with minimal chance of harbouring cancer. Accurate optical diagnosis during colonoscopy would allow small adenomas to be removed and discarded and rectosigmoid hyperplastic polyps to be left in-situ. Narrow band imaging (NBI) in expert hands allows accurate optical diagnosis and assignment of surveillance intervals.
Method The accuracy of surveillance interval assigned by NBI optical diagnosis was compared with the current reference standard of histopathological diagnosis in a prospective, blinded calibration study in 6 community hospitals in northeast England. Adults undergoing routine colonoscopy between July 2012 and February 2014 were eligible. Exclusion criteria were: inflammatory bowel disease; polyposis syndromes; pregnancy. Participating colonoscopists (n = 28) passed a validated training module utilising the NBI International Colorectal Endoscopic (NICE) classification. Optical diagnosis was provided for all polyps <10 mm and surveillance interval when only small polyps were present.
Results Of 1688 patients recruited, 723 (42.8%) had polyps <10 mm of which 567 (78.4%) only had polyps <10 mm. The sensitivity, specificity and negative predictive value of optical diagnosis (n = 499 patients) in determining the need for colonoscopic surveillance were 73.0% (95% CI: 66.9–79.9%), 75.6% (95% CI: 70.9–80.1%) and 85.2% (95% CI: 81.0–89.1%). The sensitivity and specificity per polyp (n = 1620 polyps) was 76.1% and 77.5%. If ≥ 2 NICE features were identified, then sensitivity was 95–100%.
Conclusion The findings of this study suggest that NBI optical diagnosis cannot yet be recommended for use in routine clinical practice. Sensitivity per polyp was acceptable when ≥2 NICE features were present. Further work is required to determine if variation is due to colonoscopist or polyp characteristics.
Disclosure of interest None Declared.