Assessing empirical thresholds for investigation in people referred on a symptomatic colorectal cancer pathway: A cohort study utilising faecal immunochemical and blood tests in England

Abstract

Objective To quantify risk of colorectal cancer (CRC) at empirical FIT cut offs, across age, haemoglobin and platelet strata in current diagnostic pathways. Design Cohort study of all people who were referred on a symptomatic CRC diagnosis pathway from primary care with a FIT test in Nottingham, UK between November 2017 and 2021 with 1-year follow-up for cancer and death. Heat maps showed the cumulative 1-year CRC risk using Kaplan-Meier estimates. We estimated the number of investigations that could potentially be re-purposed if a threshold of >=3% 1-year risk of CRC was instigated. Results During the study period 514 (1.5%) colorectal cancers were diagnosed following 33694 index FIT tests with available blood tests. Individuals with a FIT >=10 microg Hb/g faeces had a greater than 3% risk of CRC, except patients under the age of 40 years (CRC risk 1.45% (95% CI 0.03-2.86%)). Non-anaemic patients with a FIT =3% CRC threshold in patients < 55 years calculated using FIT, age and anaemia would allow 160-220 colonoscopies per 10000 FIT tests to be used for other pathways, at the cost of missing 1-2 CRCs. Conclusions CRC risk varies by FIT, age and anaemia status when fHb levels are below 100 microg Hb/g faeces. Tailored cut offs for investigation on a CRC pathway could reduce the number of investigations needed at a 3% CRC risk threshold.Copyright The copyright holder for this preprint is the author/funder, who has granted medRxiv a license to display the preprint in perpetuity. It is made available under a CC-BY 4.0 International license.