Food allergy testing 

Routine testing for food allergies is not recommended. A true food allergy is diagnosed by a thorough medical history exploring symptoms of a reproducible reaction to food in conjunction with formal testing (e.g. skin prick test, IgE testing) by an immunologist. Overdiagnosing food allergy can adversely affect quality of life and nutrition, and studies have shown that between 50 and 90% of presumed food allergies are not true allergies.¹⁹ 

Thyroid function testing 

Although commonly ordered in patients presenting with altered bowel habits, thyroid function tests rarely change the diagnostic or management outcomes of patients with IBS and, therefore, are not recommended as initial testing for IBS diagnosis.²⁰ 

Breath testing

Hydrogen breath testing to exclude small intestinal bacterial overgrowth or lactose intolerance in patients with suspected IBS is not recommended due to previously reported high false-positive rates of this test in patients with IBS.^6,21 

Management of IBS

Approach 

American and European gastroenterology guidelines advocate for the clinician to provide a confident, positive diagnosis of IBS with minimal investigations, as it reduces time to commence therapy and can better direct patients to explore therapeutic options rather than focus on pursing more investigations.^7,22 This approach is also supported by GESA’s advice to GPs.¹²ch of ‘diagnosis by exclusion’) involves initially ensuring the ROME IV criteria are met, while limiting diagnostic tests and providing careful longitudinal follow up.²² Once a positive diagnosis is made, the IBS subtype should be determined by asking the patient to record stool consistency on days that they identify abnormal bowel habit. The Bristol Stool Form scale is used to accurately record stool consistency when the patient is not on any stool-altering medications.²³ An approach to managing patients with IBS is summarised in the Figure.