Scott MacDonald, Linda MacDonald, Jon Godwin, Angus Macdonald, Michelle Thornton

Nov 19, 2021
Colorectal Disease

Aim Provisional research on the Faecal Immunohistochemical Test (FIT) for symptomatic colorectal patients has shown a high negative predictive value, but has lacked long-term patient follow-up, raising the possibility of missed diagnoses of colorectal cancer (CRC). We aim to describe the long-term diagnostic accuracy of FIT for CRC and significant bowel disease (SBD) in a symptomatic population in NHS Lanarkshire.
Method From October ’16-February ’19, all primary care referrals of symptomatic colorectal patients in NHS Lanarkshire were asked to provide a FIT. The baseline demographics, investigations and diagnoses of each patient were prospectively completed until February ’21. A FIT of ≥10μg Hb/g was considered to be positive.
Result n=5250 patients were identified(Median age 62years; 46% Male; Median follow-up 31 months) with 65.1%(n=3418) being FIT-negative. The SBD rate was 6.2% and CRC rate was 2.9%(n=151). The SBD rate was significantly higher in the FIT-positive group (13.8%v2.2%;p<0.001) and 32.9% of patients with FIT≥400 had SBD. The sensitivity of FIT≥10 for CRC was 87.4% and for SBD was 76.9%. Specificity was 66.6% and 66.7%, and negative-predictive value was 99.4% and 97.7% respectively. Sensitivity for CRC could theoretically be increased to 94.8% if FIT-negative patients were to undergo flexible sigmoidoscopy.
Conclusion A FIT-only referral pathway for symptomatic colorectal patients will miss over 12% of cancers and over 23% of SBD. Theoretically, combining FIT-negative patients with flexible sigmoidoscopy increases the sensitivity for CRC. FIT offers a mechanism for prioritising patient access to investigations, particularly in resource-limited areas, however, further work to identify FIT-negative patients diagnosed with CRC is required.

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