Diagnostic Approach for Chronic Diarrhea

Initial Diagnostic Steps

The British Society of Gastroenterology recommends serological testing for celiac disease as part of the initial assessment in primary care for patients with chronic diarrhea, alongside thyroid function tests and basic blood work 2
The American Gastroenterological Association suggests that IgA tissue transglutaminase antibody with total IgA level should be used to screen for celiac disease and detect IgA deficiency, which would cause false-negative results 1, 2
Thyroid-stimulating hormone (TSH) should be tested to exclude hyperthyroidism, a recognized cause of chronic diarrhea 2
Complete blood count should be assessed for anemia, which would suggest organic disease 2
Inflammatory markers (ESR or CRP) may help identify inflammatory bowel disease if elevated, although their utility in this setting is limited 1
Fecal calprotectin can distinguish inflammatory from non-inflammatory causes, but its role in the absence of alarm features is debated 1

Colonoscopy with biopsies is not indicated initially in patients under 50 without alarm features, but should be performed if age ≥50 years, presence of alarm features, or symptoms refractory to treatment after excluding celiac disease and thyroid dysfunction 1, 2
Microscopic colitis should be considered if symptoms persist despite negative initial workup, as it affects 10% of patients with chronic watery diarrhea and has a 33.4% prevalence of IBS-like symptoms 1
Abdominal CT would only be appropriate if alarm features develop, suspicion for inflammatory bowel disease with elevated inflammatory markers, or concern for complications of known disease 1, 2, 3

The British Society of Gastroenterology explicitly recommends serological testing for celiac disease as part of the initial assessment in primary care for patients with chronic diarrhea 2
The American Gastroenterological Association suggests that celiac disease should be excluded before making a functional diagnosis of irritable bowel syndrome-diarrhea (IBS-D) or functional diarrhea 1