Table 5. Reasons for difficulty in recognising IBD as source of symptoms.

Atypical presentations: Few or no prototypical features or unexpected test values, such that the correct diagnosis is either not generated or is rejected as not conforming to the clinician’s disease prototype.	Six patients presented with constipation, when IBD is prototypically associated with stool looseness: “I didn’t fit the boxes because of the constipation and my weight was stable so nobody thought about looking into Crohn’s” (P11)
Non-specific presentations: symptoms that do not easily discriminate between different potential diagnoses (IBS, coeliac, dyspepsia, etc).	“He just kept basically diagnosing me with. . . stomach-ache” (P14) “They were testing for coeliac. I cut all wheat and everything out (P10)
Uncommon conditions less likely to be considered [42]: Clinicians think only ‘pathognomonic’ indicators, those that are specific to a particular disease, will make a more uncommon disease more likely. Even when indicators (e.g. elevated faecal calprotectin) are present doctors may be cautious, because of the possibility of false positives.	In this example, a GP requested a second stool sample, which recorded insufficiently high calprotectin to detect Crohn’s disease, which was finally diagnosed ten years later, and the GP defaulted to the more common diagnosis of IBS: “I needed two stool samples with high enough markers to be referred to gastro and [the second] wasn’t high enough, and [I was told] that it was probably the IBS playing up and just to change my diet again.” (P11).
‘Diagnostic overshadowing’[43]: where a patient has another condition which provides a credible explanation for symptoms or alters the presentation. It can be particularly easy to explain away symptoms if they can be attributed to pre-existing conditions or health states (such as pregnancy) [44].	“They looked at that and thought, right the blood is from the haemorrhoids.” (P17) “Before I was 20, I’d got a diagnosis of hyper-mobility, fibromyalgia and IBS… and… a couple of mental health problems… I walk into the doctor’s and everything is put down to them… they won’t do any tests, they won’t do anything… the past twenty years where I’ve been gas-lit and told everything was in my head.” (P11, Crohn’s disease)
Lack of knowledge of linked conditions. Uveitis is a rare autoimmune disease of the eye, that often occurs in combination with other systemic diseases, requiring collaborative work-up [45–47] between general practitioners, ophthalmologists, rheumatologists, neurologists and gastroenterologists [48], although this does not always happen. In isolation, it should trigger investigations for IBD [49].	“I had the eye infection. . . And I went to the hospital, and they told me that I had uveitis. . . then [12 months later] I was losing a lot of blood. . . . I had, like, a really massive diarrhoea… every half an hour I was going to the bathroom and I was losing a lot of blood. . .” (P06, ulcerative colitis)