Diagnostic Approach to Irritable Bowel Syndrome

Clinical Features and Diagnostic Criteria

The British Society of Gastroenterology guidelines state that patients over 50 years or with family history of colorectal cancer should undergo colonoscopy regardless of symptom pattern 4
The American College of Gastroenterology recommends colonoscopy is mandatory when weight loss is present, as this constitutes an alarm feature requiring exclusion of colorectal cancer 6
Female sex and age <45 years increase likelihood of IBS 3
A 6-month symptom duration with fluctuating pattern is characteristic of IBS 2
Cardinal symptoms of IBS include abdominal pain associated with altered bowel habit, bloating, and symptom exacerbation with stress and food intake 1
Bloating and visible distension are highly suggestive of IBS when present with cardinal symptoms 1
Symptom triggers such as pain aggravated by food intake and stress demonstrate gut-brain axis dysfunction typical of IBS 1, 2
Extraintestinal symptoms like palpitations, easy fatigability, and weight loss can represent somatoform features commonly associated with IBS 2, 3

Functional dyspepsia with IBS overlap should be considered, especially with epigastric pain as a predominant feature 5
Celiac disease must be excluded with tissue transglutaminase IgA antibodies and total IgA level, as it commonly presents with chronic abdominal symptoms, weight loss, and altered bowel habits 6, 4
Microscopic colitis should be considered given the alternating diarrhea and constipation pattern, and requires colonoscopy with right and left colon biopsies for diagnosis 2, 6
Bile acid diarrhea (BAD) should be considered in the diarrheal phases of symptoms, and can be diagnosed with SeHCAT scanning or serum 7α-hydroxy-4-cholesten-3-one testing 2, 1
Inflammatory bowel disease (early/mild) is less likely given normal CBC and only minimally elevated inflammatory markers, but fecal calprotectin should be tested to definitively exclude IBD 1, 6, 4
Colorectal cancer (lower probability but must exclude) is a concern due to family history of colon cancer, and colonoscopy is mandatory despite young age 6, 4

Celiac serology (tissue transglutaminase IgA with total IgA level) is mandatory in all patients with chronic abdominal symptoms 6, 4
Fecal calprotectin should be tested to exclude inflammatory bowel disease in patients under 45 with diarrhea 1, 6, 4
Colonoscopy with biopsies is indicated due to family history of colon cancer, weight loss as an alarm feature, and need to exclude microscopic colitis and early IBD 6, 4, 1
Upper endoscopy should be considered if celiac serology is positive or if epigastric symptoms persist 5, 6

Patient education about the gut-brain axis and how diet, stress, and emotional responses impact symptoms is essential 1, 5
Dietary modifications such as a low FODMAP diet trial and avoiding trigger foods identified by the patient can be beneficial 1
Addressing psychological factors such as anxiety, depression, and stress management needs is crucial 2, 3
Setting realistic expectations that IBS is chronic with no cure, and treatments aim to improve quality of life is important 1