There is considerable interest from patients, charities and healthcare providers in how to reduce the time-to-diagnosis of IBD. While streamlining primary and secondary pathways is important, arguably because the interval between symptom onset and seeking help is the longest component of the time-to-diagnosis, novel interventions should be aimed at reducing patient delay.13  

Symptom awareness campaigns are being actively pursued, for example by Crohn’s & Colitis UK with their ‘cut the crap’ programme,19 but whether they change self-referral behaviour, is unknown. In this regard, the UK Government‘s ‘Be Clear on Cancer’ awareness campaign, which highlighted the importance of presenting to primary care with rectal bleeding to exclude bowel cancer, despite being well-funded, was ultimately ineffective.20 21 An alternative, but more contentious approach, would be to use these campaigns to promote not only disease awareness but also direct-to-public stool biomarker testing.

We have shown here that in the UK, online direct-to-public calprotectin testing is readily available from multiple providers with turnaround times under 14 days. Consumers can choose between home-based lateral flow tests that return a quantitative or semiquantitative result or send stool samples for gold-standard laboratory testing. While the laboratory tests are considerably more expensive and take longer, they are reportedly more accurate.22 23 Across the available methods comparison studies, and allowing for false negatives in mild terminal ileal Crohn’s disease,15 the diagnostic accuracy of the lateral flow platforms seems to be adequate around the positivity threshold to distinguish IBD from the irritable bowel syndrome but not at higher calprotectin concentrations.24 25 About half of providers included information regarding the context for use of calprotectin testing. Previous studies suggest that adding an assessment of the duration and presence of gastrointestinal alarm symptoms increases the diagnostic accuracy of calprotectin testing for IBD.15 However, because these tests are open to allcomers from multiple competing providers, stipulating testing only in the presence of symptoms, while best-practice, seems unfeasible.

There is no gold-standard analytical method for the measurement of calprotectin nor reference material to calibrate assay reporting to. Consequently, there is marked interassay variability in calprotectin reporting. It is somewhat surprising then that most of the assays reported here use a positivity threshold of 50 µg/g. This may reflect a lack of access to biological samples to define positivity thresholds. By way of example, we like others have shown that compared with conventional calprotectin ELISAs, the OCS assay has a positive bias across the calprotectin reporting range.26 27 That said, it seems inevitable that assays employing a stool picker collection device will supersede conventional ELISAs because they are cheaper, easier to automate, do not involve laboratory staff preprocessing stool samples and laboratories already process FITs using this platform.

We observed marked heterogeneity across collection kits in the ease of reading of patient instructions and the quality and type of visual materials. Understanding how to use test kits is important because preanalytical processing of stool samples can significantly influence the results of the home and OCS assays in particular. Both rely on the consumer transferring a sample of stool into a diluent ready for testing. Their accuracy depends on not over or underfilling the sampling device, accurately measuring the diluent and complete mixing of the stool sample and diluent, which in part depends on the composition of the initial stool.28

Recommendations for ongoing care following both a positive and negative result were frequently linked to further contact with primary care. It is critical to consider what impact the increasing use of these tests by the public will be on primary and secondary care pathways.29 As the incidence of IBD at least in the industrialised North and East of Europe is stable, we do not anticipate diagnosing significantly more patients with IBD.30 31 However, because these tests are open to all, before they can be recommended by public healthcare bodies and IBD charities, further work is needed to define the positive and negative predictive values of calprotectin testing when used in this way.4

For the time being the risk of overwhelming secondary care colonoscopy services with false positive results should be mitigated by confirmatory laboratory tests for at least intermediate results.32 In this regard, close attention will need to be paid to managing patient expectations of the need for further tests where there are discordant sequential results.

Increased use of direct-to-public stool testing driven by consumer demand seems inevitable. Therefore, there is an urgent need for an evidence base to inform integration of these results into referral pathways. Key to integration into conventional healthcare pathways is establishing the diagnostic accuracy of calprotectin and/or FIT used in this way and access to colonoscopy. Dedicated rapid access clinics could be designed to remove additional pressures on primary care while also safeguarding against multiple unnecessary colonoscopies.