Diagnostic Approach for Bile Acid Diarrhea

Initial Clinical Context

The British Society of Gastroenterology recommends screening for celiac disease with IgA tissue transglutaminase plus total IgA level (sensitivity and specificity >90%) in patients with chronic diarrhea 1
The American Gastroenterological Association suggests testing for Giardia using antigen test or PCR in patients with chronic diarrhea 1
The European Society of Gastrointestinal Endoscopy recommends excluding inflammatory bowel disease with fecal calprotectin in patients under age 40 2, 3
The British Society of Gastroenterology suggests considering colonoscopy with biopsies from right and left colon (not rectum) to exclude microscopic colitis, which can coexist with BAD 2, 3

The British Society of Gastroenterology strongly considers BAD testing in patients with terminal ileal resection or Crohn's disease affecting the ileum 4
The American Gastroenterological Association considers BAD testing in patients with post-cholecystectomy diarrhea (>50% may have BAD) 4, 5
The European Society of Gastrointestinal Endoscopy considers BAD testing in patients with pelvic radiotherapy or chemotherapy (>50% prevalence) 6, 7
The British Society of Gastroenterology considers BAD testing in patients with diarrhea-predominant IBS symptoms (up to 30% actually have BAD) 4, 5, 7

The British Society of Gastroenterology recommends SeHCAT as the preferred test where available, with the highest diagnostic yield among all biomarkers for BAD 6, 5, 7
The American Gastroenterological Association suggests using serum C4 as an alternative where SeHCAT is unavailable 2, 3
The European Society of Gastrointestinal Endoscopy suggests that a 7-day retention <15% indicates bile acid malabsorption 4, 5
The British Society of Gastroenterology suggests that severity grading is as follows: <5% = severe, 5-10% = moderate, 10-15% = mild 4, 5
The American Gastroenterological Association suggests that predicts treatment response: 96% response to bile acid sequestrants with <5% retention, 80% with <10%, and 70% with <15% 5

The British Society of Gastroenterology strongly recommends against using empiric bile acid sequestrant trials instead of making a positive diagnosis 2, 3
The American Gastroenterological Association suggests that lack of response to cholestyramine does not exclude BAD—44% of confirmed BAD patients fail cholestyramine alone, with half responding to colesevelam 5
The European Society of Gastrointestinal Endoscopy suggests that empiric trials lead to diagnostic uncertainty and repeat unnecessary testing 6, 5

The American Gastroenterological Association suggests that fecal lactoferrin at thresholds of 4.0–7.25 mg/g achieves 79% sensitivity and 93% specificity for identifying inflammatory bowel disease, not functional disorders like bile acid diarrhea 8
Bile acid diarrhea is a malabsorptive disorder without mucosal inflammation, so immune markers like beta-defensin-2 and MMP-9 should remain normal 9, 10

High ferritin, elevated B12, and elevated LDH suggest systemic inflammation, hemolysis, or tissue damage—none of which are features of bile acid diarrhea 9, 8
Transaminase elevation suggests hepatocellular injury or systemic inflammation, which are not features of bile acid diarrhea 9
Vitamin D deficiency can occur in any chronic diarrheal condition due to malabsorption, including bile acid diarrhea, but is non-specific 9, 8, 10

The British Society of Gastroenterology recommends that fecal calprotectin should be measured (threshold 50-60 mg/g) as the primary screening test, with colonoscopy and biopsy if positive 8
The diagnostic algorithm should include screening for celiac disease with IgA tissue transglutaminase plus total IgA level, as this can coexist with diarrhea 10
Testing for Giardia using antigen test or PCR should be considered, as chronic infection can cause inflammation 8