International guidelines and the Gastroenterological Society of Australia’s (GESA’s) IBS4GPs online treatment algorithm, recommend focusing on a positive diagnosis of IBS rather than treating IBS as a diagnosis of exclusion, as the latter approach can result in low diagnostic yield after extensive workup, with minimal impact on patient satisfaction.6,7,12 Investigations in a patient with suspected IBS should be rationalised and simple noninvasive tests used first. Younger patients with IBS (aged 16 to 45 years) tend to be overinvestigated, whereas older patients with a first presentation of IBS symptoms tend to be underinvestigated. The following outlines the recommended investigations in a patient fulfilling IBS criteria with no alarm symptoms.7,12
Initial blood and stool tests
Full blood count
All patients should have a full blood count performed. Evidence of anaemia or a raised white cell count should trigger consideration of alarm symptoms and other presentations.
Patients with coeliac disease may present with abdominal pain, bloating and/or changes in bowel habits, which is a similar clinical presentation to IBS. Patients with IBS symptoms should be screened for coeliac disease with antitissue transglutaminase IgG and IgA antibodies (sensitivity and specificity >90% in a patient without IgA deficiency).6,7,13,14
C-reactive protein, a marker of inflammation, has good positive predictive value for inflammatory bowel disease (IBD) in patients with IBS symptoms, but poor negative predictive value.7 An abnormal C-reactive protein level should lead to consideration of referral for further investigations to exclude an inflammatory bowel aetiology for the patient’s presenting symptoms.7,14