Capsule Endoscopy in Bile Acid Diarrhea
Capsule endoscopy will not show abnormalities in bile acid diarrhea, as this is a functional disorder without structural or visible mucosal changes. Bile acid diarrhea should be diagnosed using SeHCAT testing or serum 7α-hydroxy-4-cholesten-3-one (C4) measurement, not endoscopic evaluation 1.
Why Capsule Endoscopy is Not Indicated
Bile acid diarrhea is a biochemical disorder without histopathological changes. Research demonstrates that patients with chronic diarrhea and confirmed bile acid malabsorption (by SeHCAT testing) show no specific morphological abnormalities in ileal or colonic mucosa on endoscopic biopsies 2. The pathogenesis involves dysfunction of bile acid absorption and metabolism, not structural intestinal disease 3.
Role of Capsule Endoscopy in Chronic Diarrhea
The British Society of Gastroenterology guidelines specify that capsule endoscopy is recommended for assessing small bowel structural abnormalities in chronic diarrhea, not functional disorders 1. Capsule endoscopy has specific indications including:
- Suspected Crohn's disease with negative ileocolonoscopy and imaging studies 1, 4
- Celiac disease evaluation when patients cannot undergo gastroscopy (though not for initial diagnosis) 1, 5
- Obscure gastrointestinal bleeding after negative upper and lower endoscopy 4
- Small bowel neoplasms or other structural lesions 1
Correct Diagnostic Pathway for Bile Acid Diarrhea
The British Society of Gastroenterology strongly recommends making a positive diagnosis of bile acid diarrhea using SeHCAT testing or serum C4 measurement in patients with functional bowel symptoms or IBS-diarrhea 1. The guidelines explicitly state there is insufficient evidence to recommend empirical treatment trials rather than making a positive diagnosis 1.
SeHCAT Testing Interpretation
- Retention <5% at 7 days: Severe bile acid malabsorption, predicts excellent response to bile acid sequestrants 1, 6
- Retention 5-10%: Moderate malabsorption, 6 of 16 patients responded to treatment in one study 6
- Retention 10-15%: Mild malabsorption, though clinical significance is uncertain 1, 6
- Retention ≥15%: Normal, excludes bile acid diarrhea 6
Alternative Diagnostic Test
Serum C4 (7α-hydroxy-4-cholesten-3-one) levels >47.1 ng/mL indicate bile acid diarrhea, with 95% negative predictive value compared to SeHCAT 1. This requires a fasting sample and has limitations including diurnal variation and false positives in liver disease 1.
Clinical Context Where Both May Be Relevant
The only scenario where capsule endoscopy might be considered alongside bile acid testing is in Crohn's disease patients with chronic diarrhea. In this specific population:
- 97.4% of Crohn's disease patients with chronic diarrhea in remission had bile acid malabsorption (100% in those with prior bowel resection) 7
- Capsule endoscopy would be indicated to assess for active small bowel Crohn's disease when ileocolonoscopy and cross-sectional imaging are negative 1
- However, these are separate diagnostic questions: capsule endoscopy evaluates for mucosal inflammation/strictures, while SeHCAT/C4 testing diagnoses bile acid malabsorption 1, 7
Critical Pitfall to Avoid
Do not use capsule endoscopy as a screening or diagnostic tool for bile acid diarrhea. Approximately one-third of patients labeled with IBS-diarrhea actually have bile acid diarrhea 1, but this diagnosis requires biochemical testing (SeHCAT or C4), not endoscopic visualization 1. Capsule endoscopy is expensive, time-consuming, and carries a 3.6% retention risk even in suspected (non-established) small bowel disease 4, making it inappropriate when the suspected diagnosis is a functional disorder without structural changes 2.