A cohort study of duplicate faecal immunochemical testing in patients at risk of colorectal cancer from North-West England

Abstract

ObjectivesWe sought to investigate if duplicate faecal immunochemical testing (FIT) sampling improves the negative and positive predictive value of patients thought to be at risk of colorectal cancer (CRC). Specifically, we aimed to investigate whether the proportion of FIT-negative CRC missed by a single FIT test in symptomatic patients could be reduced by duplicate FIT testing.DesignA retrospective service evaluation cohort study of the diagnostic accuracy of duplicate FIT testing.SettingPatients referred from primary care with suspected CRC to four secondary care trusts in North-West England.Participants28 622 patients over 18-years-old with lower gastrointestinal symptoms suggestive of CRC who completed two FIT samples.Primary and secondary outcome measuresThe performance of duplicate FIT for detecting CRC at a threshold of 10 µgHb/g.ResultsThe sensitivity if either test was >10 µgHb/g was 0.978 (0.955–0.989), specificity was 0.662 (0.657–0.668), positive predictive value 0.031 (0.028–0.035) and negative predictive value 1.00 (0.999–1.00). Despite two-thirds of patients (18952) being negative following two tests, at this threshold only seven CRC were missed over a 26-month period. All seven patients had other high-risk features which should have prompted investigation.ConclusionsThis study suggests that in routine NHS practice, a duplicate FIT sample strategy together with clinical evaluation for evidence of anaemia and weight loss is superior to a single FIT sample alone and would allow symptomatic patients to be managed in primary care without the need for urgent referral to secondary care for urgent colonic imaging.

Double faecal immunochemical testing in patients with symptoms suspicious of colorectal cancer

“…Previous smaller studies have compared one against two FITs in symptomatic patients with mixed results, from no benefit from a second test 17 , to improved sensitivity for colorectal cancer 18 and advanced colorectal neoplasia 19 . The rates of discordance in these studies varied from 6.1 to 15.3 per cent 11,18 . Previous studies did not systematically report discordance between repeat tests, in the same patient over time, and the relationship to significant bowel pathology.…”

Understanding colorectal cancer risk for symptomatic patients in primary care: A cohort study utilising faecal immunochemical tests and blood results in England

“…However, these tools have used different combinations across the full range of fHb results—it is unlikely that any marker will add to the value of high fHb (≥100 μg Hb/g faeces or similar). Reduction of missed CRC below any threshold for urgent referral, based on an FIT result alone or in combination with other markers, may be improved by repeat testing 24,25 . We have not included the repeat‐tested group in our analysis.…”

“…Reduction of missed CRC below any threshold for urgent referral, based on an FIT result alone or in combination with other markers, may be improved by repeat testing. 24,25 We have not included the repeat-tested group in our analysis. Although further work is required to validate this approach the 'cost'-financial and otherwise of a missed CRC is much higher than that of a repeat FIT.…”

Efficacy and accuracy of faecal sampling by a digital rectal examination for faecal immunochemical testing

“…18,19 Therefore, we suggest that FIT via DRE could also be applied in primary care as a rule out investigation for potential TWW patients. Furthermore, there is interest growing for repeat FIT to further improve sensitivity [20][21][22] in this situation, DRE sampling may also be the method of choice to obtain the additional test. If a routine referral to secondary care has been made due to a negative FIT from primary care, the specialist may find a second sample via DRE helpful to further determine the need for invasive colonic investigation.…”