The performance of faecal immunochemical test for the detection of colorectal neoplasm and the role of proton pump inhibitors in their diagnostic accuracy.

Chandrapalan, Subashini; Hee, Siew Wan; Widlak, Monika M; Farrugia, Alexia; Alam, Mohammed T; Smith, Steve; Arasaradnam, Ramesh P

BACKGROUND Faecal immunochemical test (FIT) is currently utilised in both symptomatic and screening population, but little is known on factors that impact 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. AIM To evaluate FIT performance for the detection of colorectal neoplasm and the impact of PPI therapy on their diagnostic accuracy. METHODS Symptomatic patients referred on suspected cancer pathway and those on polyp surveillance between 2015 and 2019 were approached to participate. Accuracy estimates of FIT at different cut-off levels in diagnosing colorectal neoplasm were evaluated. Logistic regression was used to assess the effect of PPIs on FIT. RESULTS A total of 667 participants were eligible for final analysis. At 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% confidence interval, CI, 0.71 to 0.94) and 0.81 (95% CI, 0.78 to 0.84), respectively. For the detection of advanced neoplasia, the sensitivity was 0.70 (95% CI, 0.58 to 0.79) and the specificity was 0.83 (95% CI, 0.80 to 0.86). At higher thresholds, the sensitivity steadily declines whilst specificity increases. PPI therapy did not have a significant effect in the performance of FIT. CONCLUSIONS 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.