Coeliac Uk (charity) had a campaign 2015 to improve diagnosis of coeliac disesase (CD). They arranged with 15 pharmacies to talk to any customer collecting prescriptions/pills of iron deficiencey anaemia or IBS from them & ask if they had ever been tested for CD. If the person hadn't, they offered a test at the pharmacy.
551 people were tested - 52 (9.4%) were positive for CD & later went on to have confirmation by more complex tests.
Interesting isn't it? This is a very small survey but reinforces to me that the message is look for ALL the obvious potential causes of IBS first.