Bile acid malabsorption (BAM)

Bile acid malabsorption (BAM): the overlooked cause of chronic diarrhoea

Bile acid malabsorption (BAM) is a common but often overlooked cause of chronic diarrhoea. It is present in a substantial share of patients otherwise labelled with diarrhoea-predominant irritable bowel syndrome (IBS-D); the reported share varies between studies and depends on the test used [1]. BAM occurs when bile acids from the gallbladder are not properly reabsorbed in the distal ileum and instead enter the colon, where they stimulate water and electrolyte secretion → watery diarrhoea.

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Three types

Type	Cause
Type 1	Ileal disease: Crohn's, ileal resection, radiation
Type 2	Primary - defective FGF19 feedback
Type 3	Secondary: cholecystectomy, SIBO, coeliac, chronic pancreatitis

How the types are distributed varies between case series and depends on which patients are investigated, so we do not give fixed percentages here.

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Symptoms

• Watery, yellow-green diarrhoea - often several times daily
• Urgent need to defecate and fear of incontinence
• Nocturnal diarrhoea - atypical for IBS, suspicious for BAM or IBD
• Cramps, bloating, flatulence
• Weight loss and fat-soluble vitamin deficiencies in severe disease
• Often worse after fatty meals

Key clinical pointer: Chronic diarrhoea after gallbladder surgery is a recognised problem, and bile acid malabsorption is one possible explanation. How often it happens varies between reports, and we do not give a pooled figure here.

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Diagnosis

1. SeHCAT scan - a validated nuclear medicine test, where available. Measures whole-body retention of a radiolabelled bile acid analogue (75Se) 7 days after ingestion. Per the BSG chronic diarrhoea guideline, 7-day retention of 10-15 % is typically graded as mildly abnormal, 5-10 % as moderately abnormal, and below 5 % as severely abnormal; retention below 15 % is used as the threshold at which a trial of bile acid binders can be considered [2,4]. Interpretation is done by the nuclear medicine department/specialist, not by the patient.
2. Serum C4 (7α-hydroxy-4-cholesten-3-one) - indirect marker of bile acid synthesis; raised in BAM.
3. Faecal bile acids (48-hour collection) - alternative if SeHCAT unavailable.
4. Empirical treatment trial with bile acid binders in patients with high clinical suspicion. A good response supports the diagnosis but does not prove it on its own, since symptom relief can also occur with other causes of diarrhoea.

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Treatment

Bile acid binders (the treatment the BSG chronic diarrhoea guideline points to as the first therapeutic trial in bile acid malabsorption [4]):

• Cholestyramine - cheap, but unpleasant taste and several drug interactions.
• Colesevelam - usually better tolerated.
• Colestipol - alternative.

The dose is titrated individually by the treating doctor and is not stated here. Never stop or change prescribed medication without a specific agreement with the treating doctor.

Bile acid binders can affect the absorption of other medicines and of fat-soluble vitamins. Which medicines this applies to, and how much time to leave between the binder and your other medication is stated in the product information for the specific preparation and is agreed with your doctor or pharmacist.

Dietary advice:

• Some people have fewer symptoms when dietary fat is reduced. There is no universal gram limit; changes should be adapted to nutritional status, symptoms and other treatment with a doctor or dietitian
• Avoid alcohol
• Supplement fat-soluble vitamins (A, D, E, K) in severe disease

Treat underlying cause (type 1 and 3) - IBD control, SIBO eradication, coeliac diet.

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Why is it missed?

• SeHCAT is not universally available
• Symptoms mimic IBS-D
• Many patients are diagnosed only after 5+ years
• Empirical treatment trials are often skipped in primary care [3]

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Treatment at Kirurgen.dk

We investigate chronic diarrhoea with colonoscopy, gastroscopy, coeliac screening and faecal calprotectin - and refer for SeHCAT when BAM is suspected. See also: Chronic diarrhoea, IBS, SIBO, Microscopic colitis.

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References

1. Wedlake L, A'Hern R, Russell D, et al. Systematic review: the prevalence of idiopathic bile acid malabsorption as diagnosed by SeHCAT scanning in patients with diarrhoea-predominant irritable bowel syndrome. Aliment Pharmacol Ther 2009;30(7):707-17.
2. Vijayvargiya P, Camilleri M, Shin A, Saenger A. Methods for diagnosis of bile acid malabsorption in clinical practice. Clin Gastroenterol Hepatol 2013;11(10):1232-9.
3. BSG guidelines on the management of functional bowel disorders. Gut 2021;70:1214-40.
4. Arasaradnam RP, Brown S, Forbes A, et al. Guidelines for the investigation of chronic diarrhoea in adults: British Society of Gastroenterology, 3rd edition. Gut 2018;67:1380-1399. gut.bmj.com/content/67/8/1380