Can FIT rule out colorectal cancer in symptomatic patients? Diagnostic test accuracy results from 9,822 patients in the NICE FIT study.

Abstract

4093 Background: The faecal immunochemical test (FIT) is a non-invasive quantitative test that measures occult blood in faeces (faecal haemoglobin, FHb). FIT is already used worldwide in colorectal cancer (CRC) screening programmes. Bowel symptoms have low specificity for CRC; to diagnose one patient with CRC, a large number of symptomatic patients require investigation. A negative FIT test, when blood is not detected, could be used to rule out CRC in symptomatic patients without invasive investigations such as colonoscopy. We report on the largest diagnostic accuracy study to date of FIT in symptomatic patients. Methods: Patients were eligible for recruitment if they experienced bowel symptoms meeting national high-risk criteria and were triaged to investigation with colonoscopy. Patients were excluded from analysis if they did not provide a valid FIT or did not undergo complete colonoscopy. Colonoscopy results were compared to FIT measurements of FHb, and the conduct of the tests was double-blinded. Quality assurance of endoscopy and clinical data was performed by senior clinicians. External statisticians analysed anonymised data. Results: 9822 patients from 50 sites across England participated in the study between October 2017 to March 2019. The most common colonoscopy finding was absence of any colorectal disease (31%). The prevalence of CRC at colonoscopy was 3.3%. The sensitivity of FIT at FHb thresholds of 2, 10 and 150 μg/g significantly decreased from 97.0% to 90.9% and 70.8% respectively (p < 0.01). FIT positivity rate at these thresholds increased from 7.6%, to 19% and 37.2% respectively (p < 0.01). The positive predictive value of FIT for CRC at FHb thresholds of 2, 10 and 150 μg/g was 8.7%, 16.1% and 31.1% respectively and the negative predictive value of FIT at these thresholds was 99.8%, 99.6% and 98.9% respectively. Conclusions: The results of this study support the use of FIT at the threshold of detectable blood (2μg/g) as an initial CRC rule-out test to triage patients with high risk CRC symptoms, reducing the number of unnecessary investigations. This is the first study to report that at the lowest threshold of detectable blood, FIT sensitivity is equivalent to the current gold standard investigation of colonoscopy. Clinical trial information: ISRCTN49676259 .