Introduction Flexible sigmoidoscopy (flex sig) remains a cornerstone for colorectal cancer (CRC) screening in the UK although concerns have been raised about about isolated proximal neoplasia which is especially common in women.1 Our group has demonstrated using novel polarisation-gated spectroscopy (4D-ELF) that peri-cryptal microvascular blood supply is elevated in the histologically normal mucosa of patients harboring neoplasia elsewhere in their colon (marker of field effect).2–4⇓⇓ We, therefore, wanted to investigate whether this could serve as an adjunct to flex sig.

Methods Subjects undergoing colonoscopy were recruited. Microvascular readings were taken from the endoscopically normal rectum with a fibreoptic probe and analysed by an investigator blinded to colonoscopic findings. Specifically, superficially (within 100 micron of tissue surface) oxygenated hemoglobin (SupOxyHb) was calculated. Proximal lesions were defined at the level of the spenic flexure. The performance of distal adenoma and microvascular blood content was calculated. Advanced adenomas (AAs) were defined as size ≥1.0 cm or presence of high-grade dysplasia.

Results Our initial data set consisted of 366 patients (age 58±10, 50% female, 28 with AA). Distal adenoma performed poorly at identifying risk proximal AA (sensitivity 11%). Rectal SupOxyHb was elevated by approximately 50% in patients harboring proximal AA (when compared to neoplasia free patients) with an area under receiver operator characteric curve (AUROC) of 0.83. On a separate data set (n=172), the results were validated with an AUROC of 0.84. With regards to gender, the performance in females was excellent. (AUROC=0.88). SupOxyHb was not confounded by demographic factors or benign colonic disease (including hyperplastic polyps) and was insensitive to non-advanced adenomas.

Conclusion We demonstrate, for the first time, that evaluation of rectal microvascular hemoglobin was able to sense proximal advanced adenomas with excellent accuracy, markedly outperforming the sentinel adenoma (a conventional marker of field effect). We replicated these results with an independent data set. Furthermore, SupOxyHb worked well in women, a group in which flex sig performs relatively poorly. Our data suggest that rectal EIBS measurement may provide an accurate and inexpensive means of improving performance of flex sig for CRC screening.