Performance of the faecal immunochemical test for the detection of colorectal neoplasms and the role of proton pump inhibitors in their diagnostic accuracy

Aim: The faecal immunochemical test (FIT) is currently utilized in both symptomatic and screening populations, but little is known about factors that affect its performance. For example, proton pump inhibitor (PPI) therapy has been purported to increase false negative rates. This has significant implications given the extent of PPI prescriptions. The aim of this work was to evaluate the performance of the FIT for the detection of colorectal neoplasms and the impact of PPI therapy on its diagnostic accuracy. Method: Symptomatic patients referred on the suspected cancer pathway and those on polyp surveillance between 2015 and 2019 were approached to participate. Estimates of the accuracy of FIT at different cut-off levels in diagnosing colorectal neoplasms were made. Logistic regression was used to assess the effect of PPIs on the FIT results. Results: A total of 667 participants were eligible for the final analysis. At a cut-off of 10 μg/g faeces, the overall sensitivity and specificity of FIT for the detection of colorectal cancer (CRC) was 0.85 (95% CI 0.71–0.94) and 0.81 (95% CI 0.78–0.84), respectively. For the detection of advanced neoplasia, the sensitivity was 0.70 (95% CI 0.58–0.79) and the specificity was 0.83 (95% CI 0.80–0.86). At higher thresholds, the sensitivity steadily declined whilst specificity increased. PPI therapy did not have a significant effect on performance of the FIT. Conclusion: FIT is a good rule-out test for the detection of CRC and advanced neoplasia at lower thresholds. PPI therapy does not appear to have an effect on its diagnostic performance.