Introduction Studies have suggested that organic diseases particularly bile acid diarrhoea/malabsorption, carbohydrate malabsorption, microscopic colitis, pancreatic exocrine insufficiency and small intestinal bacterial overgrowth, may be misdiagnosed as irritable bowel syndrome (IBS). We conducted a systematic review and meta-analysis of the prevalence of these conditions in adults with IBS-like symptoms.

Methods PubMed, EMBASE, CINAHL and Cochrane were searched from January 1978 (1st publication of the Manning Criteria) to July 2019. Studies were included if they prospectively or retrospectively evaluated the prevalence of any of these conditions in consecutive patients meeting Manning, Kruis or Rome I-IV criteria for IBS. These disorders were defined as follows: Bile acid diarrhoea/malabsorption –a ⁷⁵Selenium taurocholic acid scan (SeHCAT) with 7-day retention <15%; Carbohydrate malabsorption - a positive lactose, fructose, sucrose, sorbitol or mannitol breath test; Microscopic colitis - abnormal histological findings on colonic biopsies meeting criteria for lymphocytic or collagenous colitis; Pancreatic exocrine insufficiency - faecal elastase level <200 μg/g; Small intestinal bacterial overgrowth- a positive lactulose (LHBT) or glucose hydrogen breath test (GHBT), or a bacterial count of >10⁵ cfu/mL in the jejunal aspirate.

Results Bile acid diarrhoea/malabsorption: the pooled prevalence of an abnormal scan in 8 studies (n=706) was 36.1%.

Carbohydrate malabsorption: 36 papers (n=7,667) gave a pooled prevalence of a positive lactose, fructose, sorbitol or mannitol breath test as 47.4%, 67.8%, 60% and 20%, respectively.

Microscopic colitis: the pooled prevalence from 16 studies (n=4,770) was 2.9%.

Pancreatic exocrine insufficiency: the pooled prevalence from 2 papers (n=478) was 4.6%.

Small intestinal bacterial overgrowth: 32 and 18 studies (n=4,381 and 1,710) used LHBT and GHBT giving a pooled prevalence of a positive LHBT or GHBT of 40.4% and 26.5% respectively. Prevalence was 18.3% from the 5 studies (n=448) using bacterial count.

There was significant heterogeneity in effect sizes of each of these conditions.

Conclusion Systematic review suggests that organic conditions in the gastrointestinal tract in patients with IBS-like symptoms are not rare. The need to exclude these treatable organic disorders systematically will be challenging in clinical practice in view of the large number of patients presenting with these symptoms. Future international guidelines on management of IBS should be revised accordingly.