Faecal Immunochemical Testing to Detect Colorectal Cancer in Symptomatic Patients: A Diagnostic Accuracy Study

(1) Background: NHS England recommended faecal immunochemical testing (FIT) for symptomatic patients in June 2020 to rationalise limited diagnostic services during COVID-19. (2) Aim: to investigate the diagnostic performance of FIT, analysing the proportion of FIT-negative colorectal cancers (CRC) missed in symptomatic patients and how this risk could be mitigated. (3) Design and Setting: a retrospective study of biochemistry and cancer databases involving patients referred from primary healthcare with suspected CRC to a single secondary care trust in North East London. (4) Methods: a retrospective cohort diagnostic accuracy study was undertaken to determine the performance of FIT for detecting CRC at 10 & mu;gHb/g. (5) Results: between January and December 2020, 7653 patients provided a stool sample for FIT analysis; 1679 (22%) samples were excluded due to inadequate or incorrect specimens; 48% of suspected CRC referrals completed FIT before evaluation; 86 FIT tested patients were diagnosed with histologically proven CRC. At 10 & mu;gHb/g, FIT performance was comparable with the existing literature with a sensitivity of 0.8140 (95% CI 0.7189-0.8821), a specificity of 0.7704 (95% CI 0.7595-0.7809), a positive predictive value (PPV) of 0.04923 (95% CI 0.03915-0.06174), a negative predictive value (NPV) of 0.9965 (95% CI 0.9943-0.9978), and a likelihood ratio (LR) of 3.545; 16 patients with CRC had an FIT of & LE;10 & mu;gHb/g (18.6% 95% CI 11.0-28.4%). (6) Conclusions: this study raises concerns about compliance with FIT testing and the incidence of FIT-negative CRC at the NICE recommended threshold and how this risk can be mitigated without colonic imaging. Whilst FIT may have facilitated prioritisation during COVID-19, we must be cautious about using FIT alone to determine which patients are referred to secondary care or receive further investigation.

Automated summary

This study investigated the diagnostic performance of FIT in symptomatic patients, analyzing the proportion of FIT-negative colorectal cancers (CRC) missed and how to mitigate this risk. The results showed that FIT had comparable performance with the existing literature in detecting CRC, but there was a certain proportion of FIT-negative CRC. Therefore, relying solely on FIT to determine referrals to secondary care or further investigations needs caution.