The diagnostic accuracy of the faecal immunochemical test for colorectal cancer in risk-stratified symptomatic patients.

INTRODUCTION: The faecal immunochemical test detects blood in the faeces, reporting faecal haemoglobin quantitatively in micrograms of haemoglobin per gram of faeces. The aim of this pilot study was to determine the feasibility of using the faecal immunochemical test as a rule-out test in symptomatic patients at low and high risk of colorectal cancer.
MATERIAL AND METHODS: Between November 2016 and October 2017, consecutive symptomatic patients within a multicultural part of London were recruited to perform a faecal immunochemical test prior to colonoscopy. Analysis was performed on the HM-JACKarc analyser.
RESULTS: Faecal immunochemical test samples were returned by 298 patients who underwent colonoscopy. There was no significant variation in faecal haemoglobin levels by age, sex, ethnicity or deprivation. The overall detection rate for colorectal cancer was 100% at 2 µg/g and 92% at 10 µg/g. If a faecal haemoglobin threshold for investigation of 2 µg/g (ie detectable) or 10 µg/g had been employed, the number of colonoscopies would have been reduced by 70% and 84%, respectively, in all symptomatic patients. For low-risk patients, the sensitivity of the faecal immunochemical test for colorectal cancer at both thresholds of 2 µg/g or 10 µg/g remained 100%, with the number of colonoscopies reduced by 80% and 91%, respectively.
CONCLUSION: This study shows that the faecal immunochemical test is a promising technology that detected colorectal cancer in all high- or low-risk symptomatic patients in our cohort at a threshold of detectable faecal haemoglobin. Data from adequately powered cohort studies will elucidate the true diagnostic accuracy of the test and the rate and patterns of undetected colorectal cancer.