Diagnostic Approach to Irritable Bowel Syndrome

Symptom-Based Diagnosis

The American Gastroenterological Association recommends that IBS diagnosis should be based on positive identification of symptoms using the Rome criteria, which requires abdominal pain for at least 12 weeks in the preceding 12 months with at least two of three features: pain relieved by defecation, onset associated with change in stool frequency, or onset associated with change in stool form 1
The diagnosis always presumes the absence of structural or biochemical explanations for symptoms, according to the American Gastroenterological Association 1, 2

The European Society for Neurogastroenterology and Motility recommends that complete blood count (CBC) and C-reactive protein (CRP) or erythrocyte sedimentation rate (ESR) should be performed in all patients with suspected IBS 3, 4
Coeliac serology (anti-endomysial antibodies) should be checked in all patients with IBS symptoms, as recommended by the British Society of Gastroenterology 4, 5
Stool testing for occult blood (Hemoccult) is recommended for screening purposes by the American Gastroenterological Association 6
Faecal calprotectin should be tested in patients with diarrhoea under age 45 to exclude inflammatory bowel disease, according to the European Society for Neurogastroenterology and Motility 4

Patients over 50 years old or with a family history of colorectal cancer should undergo colonoscopy regardless of symptom pattern, as recommended by the American College of Gastroenterology 6, 7
Young patients (<45 years) with typical IBS symptoms and no alarm features may be safely given a working diagnosis without further testing, according to the British Society of Gastroenterology 7
For patients with IBS with diarrhea (IBS-D), consider 23-seleno-25-homotaurocholic acid (SeHCAT) scanning or serum 7α-hydroxy-4-cholesten-3-one to exclude bile acid diarrhea, as recommended by the European Society for Neurogastroenterology and Motility 3, 4
Consider lactose/dextrose H2 breath test in patients who regularly consume dairy products, especially those from high-risk ethnic groups, according to the British Society of Gastroenterology 5, 6

There is no role for colonoscopy in typical IBS without alarm features or age >50 years, as stated by the European Society for Neurogastroenterology and Motility 3, 8
Ultrasound is not recommended as it often detects incidental findings unrelated to symptoms, according to the British Society of Gastroenterology 9
Hydrogen breath testing for small intestinal bacterial overgrowth is not recommended in patients with typical IBS symptoms, as recommended by the European Society for Neurogastroenterology and Motility 3, 8
Testing for exocrine pancreatic insufficiency is not indicated in typical IBS, according to the European Society for Neurogastroenterology and Motility 3, 8

Relying solely on patient reports of food intolerances without objective testing may lead to unnecessary dietary restrictions, as noted by the British Society of Gastroenterology 5
Performing colonoscopy in young patients with typical IBS symptoms and no alarm features is not cost-effective, according to the British Society of Gastroenterology 7

The American Gastroenterological Association recommends a focused panel of tests, including CBC, celiac serology (IgA tissue transglutaminase with total IgA), fecal calprotectin, and stool testing for Giardia, to exclude organic disease in patients with suspected IBS 10
Celiac disease testing with IgA tissue transglutaminase (tTG) and total IgA level is a strong recommendation with moderate-quality evidence, as celiac disease is an important cause of chronic diarrhea and IBS-like symptoms with sensitivity >90% 10
Stool testing for Giardia is a strong recommendation with high-quality evidence, as Giardia is a common parasitic cause of chronic diarrhea 10

The American Gastroenterological Association suggests against using CRP or ESR to screen for IBD due to low-quality evidence, though some European guidelines recommend them 10
Fecal lactoferrin is an alternative to fecal calprotectin for screening IBD, with a conditional recommendation and low-quality evidence 10

Colonoscopy is not indicated in patients under 45 years with typical IBS symptoms and no alarm features, according to the British Society of Gastroenterology 11
The American Gastroenterological Association suggests against testing for ova and parasites (other than Giardia) unless there is travel history to or recent immigration from high-risk areas 10

Serologic tests for IBS diagnosis are not recommended due to insufficient evidence, with sensitivity <50% meaning negative tests cannot rule out IBS 10, 12
Ultrasound is not recommended as it often detects incidental findings unrelated to symptoms, according to the British Society of Gastroenterology 11

Approximately 20% of patients with active Crohn's disease may have normal CRP levels, so a normal inflammatory marker does not completely exclude inflammatory bowel disease, according to the Journal of Crohn's and Colitis 13

The American Gastroenterological Association recommends celiac disease screening with IgA tissue transglutaminase and total IgA level, as well as stool testing for Giardia, for patients presenting with IBS symptoms, with strong evidence and moderate quality evidence 14, 15, 16
For patients with IgA deficiency, the American Gastroenterological Association recommends using IgG-based testing, such as IgG-deamidated gliadin peptide or IgG-tTG, with strong evidence and moderate quality evidence 14, 15, 16
The American Gastroenterological Association recommends fecal calprotectin or fecal lactoferrin testing to screen for inflammatory bowel disease, with conditional recommendation and low quality evidence 14, 15, 16, 17

The American Gastroenterological Association suggests bile acid diarrhea testing in patients with IBS-D who don't respond to initial therapy, with conditional recommendation and low quality evidence 14, 15, 16, 17
Lactose breath testing is recommended for patients consuming >0.5 pint (280 ml) of milk daily, especially those from high-risk ethnic groups, with evidence from Gut 18

The American Gastroenterological Association recommends against using ESR or CRP alone to screen for IBD, with conditional recommendation against and low quality evidence 14, 15, 16, 17
The American Gastroenterological Association recommends against testing for ova and parasites (other than Giardia) unless travel history to or recent immigration from high-risk areas, with evidence 14, 15, 16, 17
The American Gastroenterological Association recommends against using serologic tests for IBS diagnosis, with no recommendation due to knowledge gap 14, 15, 16, 17
The American Gastroenterological Association recommends against performing ultrasound as it detects incidental asymptomatic findings, with evidence from Gut 18