DUPLICATE FIT TESTING AS A SAFETY NETTING STRATEGY FOR PATIENTS AT RISK OF COLORECTAL CANCER

ABSTRACT

Introduction Faecal immunochemical testing (FIT) has been shown to have an acceptable positive predictive value (PPV) and negative predictive value (NPV) for the detection of colorectal cancer (CRC). NHS-E/NICE COVID pandemic guidance recommends that patients with a FIT < 10μgHb/g do not need urgent colonic imaging but can be 'safety-netted' if not anaemic. Nonetheless concerns remain, that based on a FIT test alone up to 10% of patients with CRC might be missed by this approach, possibly due to the inherent risks of sampling error. The AIM of this study was to determine if the NPV and PPV of FIT could be improved by a strategy of duplicate FIT testing. Methods An observational cohort study of duplicate FIT testing of all patients referred on a Lower GI TWW pathway across 4 NHS provider trusts in the Lancashire and South Cumbria Cancer alliance from Jan2019-Feb 2021. FIT samples were analysed at a single centre using OC-sensor with a cut off > 10 0μgHb/g of faeces taken as a positive. CRC diagnoses were ascertained from local hospital records and cross referenced with the Somerset Cancer Registry. Results 28,622 of 30,105 (95%) referred patients (median [range] age 66y [16-103], 56% female) submitted duplicate FIT tests. 317/28,622 (1.1%) were diagnosed with CRC, of whom 22/317 (59%) were men. Of 18,952/28622 (66%) with two negative FIT tests, CRC was subsequently diagnosed in 7 patients (0.04%) with anaemia (n=7) and right sided tumours (n=6). In contrast, a single FIT strategy would have missed 22 patients of whom only 7 (32%) were anaemic. Interestingly duplicate FIT testing also improved the PPV, which increased from 0.3% if both tests were >10 - 100 0μgHb/g to a PPV of 14% if both tests were >100 0μgHb/g of faeces Conclusions A strategy of duplicate testing improves the NPV and PPV of FIT and should be considered as a mitigation to reducing missed cancer diagnosis. In patients at risk of CRC with no anaemia, duplicate FIT testing effectively rules out CRC and allows patients to be safely managed in primary care.