Patient guide · Gastroenterology
SeHCAT scan, the definitive test for bile acid malabsorption / bile acid diarrhoea.
SeHCAT (selenium-75 homocholic acid taurine) is a nuclear medicine test that measures 7-day retention of a synthetic bile acid — the definitive test for bile acid malabsorption (BAM) / bile acid diarrhoea. Requires 2 visits, 7 days apart.
Reviewed by Pulse Atlas Editorial Board, · Published 2026-07-30 · Next review 2027-07-30 · 5 min read
Key facts, in six
- 01
Definition
A nuclear medicine test that measures how much of a synthetic bile acid your gut retains at 7 days.
- 02
Two visits, seven days apart
Baseline scan on day 0, repeat scan on day 7 — the interval is the test.
- 03
How it works
Oral SeHCAT capsule (selenium-75 homocholic acid taurine) followed by a gamma camera scan.
- 04
Reading the number
Retention below 15% indicates bile acid malabsorption; below 5% is severe.
- 05
Where it fits
The foundation of the chronic diarrhoea workup once red flags are excluded.
- 06
What it complements
Sits alongside FBC, coeliac serology and faecal calprotectin — not in place of them.
The diagnostic pathway
From consultation to result — what happens, in order.
Two visits, seven days apart. Between them, a normal week — no diet change, no fasting.
Phase 1 · Before
Consultation, review, planning
Phase 2 · Days 0 to 7
Two visits, one week apart
Phase 3 · After
Result and plan
- 01
Before
Gastroenterology consultation
Consultant-led review to decide whether SeHCAT is the right next test.
- 02
Before
Baseline symptom + medication review
Stool frequency, urgency, nocturnal symptoms and any drugs that alter bile handling.
- 03
Days 0–7
Day 0: capsule + baseline scan
You swallow the SeHCAT capsule with water; a short gamma camera scan follows.
- 04
Days 0–7
Continue your normal diet
No dietary restriction between visits — eat and drink as you usually would.
- 05
Days 0–7
Day 7: return for the repeat scan
A second gamma camera scan at the same clinic, one week later.
- 06
After
Retention percentage calculated
The two scans are compared to give a retention figure and severity band.
- 07
After
A structured plan
Result, cause and a written treatment plan from your gastroenterologist.
Typical end-to-end from consultation to result: 2–3 weeks.
What it shows
The eight presentations a SeHCAT scan resolves.
SeHCAT answers one question — is bile acid malabsorption driving the diarrhoea? — and reveals which of the classical patterns is at play.
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Type 1 BAM (post-ileal resection)
After surgical removal of terminal ileum — Crohn’s, cancer or trauma.
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Type 2 BAM (idiopathic)
No obvious anatomical or metabolic cause on standard workup.
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Type 3 BAM (post-cholecystectomy, diabetes)
After gallbladder removal, or in association with diabetes and other conditions.
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Post-radiotherapy BAM
Following pelvic or abdominal radiotherapy that has affected the ileum.
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Crohn’s-related BAM
Active or burnt-out ileal Crohn’s disease impairing bile acid uptake.
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Post-infectious BAM
Persistent bile acid diarrhoea after a resolved episode of gastroenteritis.
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Refractory functional diarrhoea
IBS-D that hasn’t responded to standard treatment — SeHCAT reclassifies a meaningful share.
-
Red flag: severe BAM (< 5% retention) — urgent gastro follow-up
Severe malabsorption needs prompt consultant review, not a routine slot.
Treatment options
What follows a positive SeHCAT scan.
Treatment is directed by severity, cause and tolerance — most patients respond well to a bile acid sequestrant plus dietary support.
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Bile acid sequestrant
Cholestyramine or colestipol as first-line therapy — binds bile acids in the gut.
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Colesevelam
Better-tolerated bile acid sequestrant when cholestyramine is poorly tolerated.
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Low-fat diet
Reducing dietary fat lowers bile acid load and often improves symptoms.
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Loperamide adjunct
Symptomatic anti-motility agent used alongside sequestrants when needed.
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Vitamin ADEK monitoring
Fat-soluble vitamin levels checked and replaced in longer-term malabsorption.
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Treat the underlying cause
Directed therapy for Crohn’s, radiation enteropathy or coeliac disease where present.
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Structured gastro follow-up
Consultant review to titrate dose, confirm response and revisit diagnosis if needed.
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Multi-disciplinary team review
Dietitian, gastroenterologist and surgeon input for complex or post-surgical cases.
Red flags
When BAM needs urgent, not routine, review.
Severity of the number matters, but so does the clinical picture. These are the situations that warrant prompt gastroenterology input.
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Severe BAM with dehydration
Retention under 5% with volume loss needs prompt medical review, not a routine follow-up.
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Post-radiotherapy severe BAM
Marked malabsorption after pelvic radiotherapy warrants urgent gastroenterology input.
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Post-ileal resection dehydration
Short-bowel physiology can decompensate quickly — flag any lightheadedness or reduced urine output.
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Vitamin ADEK deficiency
Chronic fat malabsorption depletes fat-soluble vitamins — levels should be checked.
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Osteoporosis with malabsorption
Long-standing BAM raises fracture risk; DEXA and bone-health review are appropriate.
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Weight loss more than 10%
Unintentional weight loss beyond ten per cent is a red flag regardless of the scan result.
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Rectal bleeding with BAM
Bleeding is never explained by BAM alone — colonoscopy is needed to exclude other pathology.
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Coexisting IBD flare
Active inflammatory bowel disease changes the treatment plan and needs specialist review.
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Post-cholecystectomy severe BAM
Severe post-cholecystectomy BAM often needs combined sequestrant plus dietary strategy.
Frequently asked
Everything we get asked about the SeHCAT scan.
Retention thresholds, radiation dose, medication interruption, and what a positive scan actually leads to.
-
What is a SeHCAT scan?
A nuclear medicine test that measures the seven-day retention of a synthetic bile acid (selenium-75 homocholic acid taurine). It is the definitive test for bile acid malabsorption (BAM), also called bile acid diarrhoea.
-
How is retention interpreted?
Retention below 15% at seven days indicates BAM. Below 10% is moderate, and below 5% is severe. Above 15% makes BAM very unlikely.
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Do I need to fast or stop medications?
No fasting is required. Some bile acid sequestrants and cholesterol-lowering drugs need to be paused beforehand — your gastroenterologist will confirm which.
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Is the radiation dose significant?
The effective dose is low — comparable to a few months of natural background radiation. It is not used in pregnancy or breastfeeding except in exceptional circumstances.
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How long does each visit take?
Each visit is short — swallowing the capsule and the gamma camera scan together take around 30 minutes on day 0 and 15–20 minutes on day 7.
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What happens if the scan is positive?
A positive scan leads to a trial of a bile acid sequestrant (typically cholestyramine or colesevelam), with structured gastroenterology follow-up to titrate dose and confirm response.
Sources
Clinical guidance underpinning this guide.
- British Society of Gastroenterology. Guidelines on the investigation of chronic diarrhoea in adults.
- NICE. Chronic diarrhoea in adults: diagnosis and management guidance.
- European Society of Neurogastroenterology and Motility. Consensus on bile acid diarrhoea.
- American Gastroenterological Association. Clinical practice guidance on functional diarrhoea and BAM.
Related tests
Looking for a different test?
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Hydrogen breath test
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Faecal calprotectin
Screens for inflammatory bowel disease in chronic diarrhoea.
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Colonoscopy
Direct visualisation of the colon — the definitive structural test.
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All tests
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Acid Reflux
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Crohns Disease
Related condition guide.
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Colectomy
Related treatment option.
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Cholecystectomy
Related treatment option.
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In practice, in London
How sehcat scan tends to unfold when you go private
With sehcat scan, the London question is usually about report turnaround and the radiologist reading it — not whether the scan is available. Waiting lists on the NHS for sehcat scan vary widely by borough and by how the GP letter reads. Privately in London, we can normally offer a slot inside the same week, sometimes within 48 hours if there’s a cancellation. The difference isn’t clinical quality — the consultants are frequently the same faces you’d see on the NHS — it’s the calendar.
A private sehcat scan pathway in London usually looks like this: an initial consultation, any diagnostics booked at a nearby facility (most within Zone 1 or 2), and a written report sent to you and your GP within a few days. The consultants we work with hold NHS posts alongside their private lists, which keeps the standards consistent across both settings. For sehcat scan specifically, the difference between a routine report and a sub-speciality read is where private care earns its keep.
There are a lot of consultants in London who can technically handle sehcat scan. Fewer who do it week in, week out for the exact question you’re bringing. We spend most of our time working out which is which — and being straight when a different test or a different specialist would serve you better. Everything runs to CQC, GMC and Royal College standards; the choice is about fit, not floor.