Bile Acid Malabsorption Test: Complete Guide to SeHCAT Scan
📊 Quick Facts About the Bile Acid Malabsorption Test
💡 Key Takeaways About This Test
- Gold standard diagnostic test: The SeHCAT scan is the most accurate way to diagnose bile acid malabsorption with 80-94% sensitivity
- Two appointments required: The test involves two visits exactly 7 days apart to measure bile acid retention
- Low radiation exposure: The radioactive tracer used is safe with minimal radiation, similar to a chest X-ray
- Stop certain medications: You may need to pause bile acid sequestrants, opioids, and anti-diarrheal medications before testing
- Not suitable during pregnancy: Pregnant or breastfeeding women should postpone the test due to radiation exposure
- Results guide treatment: Test results determine the severity of bile acid malabsorption and help guide treatment decisions
What Is a Bile Acid Malabsorption Test?
A bile acid malabsorption test, also known as a SeHCAT scan (selenium-75 homocholic acid taurine test), is a nuclear medicine procedure that measures how well your small intestine absorbs and retains bile acids. The test compares bile acid levels on day 1 versus day 7 to determine if malabsorption is occurring.
Bile acids are chemicals produced by your liver and stored in your gallbladder. When you eat, bile acids are released into your small intestine to help digest fats. Normally, about 95% of these bile acids are reabsorbed in the terminal ileum (the last part of your small intestine) and recycled back to the liver. This process is called enterohepatic circulation and occurs multiple times per day.
When the small intestine fails to properly absorb bile acids, they pass into the large intestine (colon) where they cause water and electrolytes to be secreted, leading to watery diarrhea. This condition is called bile acid malabsorption (BAM) or bile acid diarrhea (BAD). Research shows that bile acid malabsorption affects approximately 1% of the general population, but may be present in up to 30% of patients diagnosed with diarrhea-predominant irritable bowel syndrome (IBS-D).
The SeHCAT test works by having you swallow a capsule containing a synthetic bile acid labeled with a small amount of radioactive selenium-75. This tracer behaves exactly like natural bile acids in your body but can be detected by a gamma camera. By measuring how much of the tracer remains after 7 days, doctors can accurately determine whether bile acid malabsorption is contributing to your symptoms.
Why Is This Test Performed?
Your doctor may recommend a bile acid malabsorption test if you have chronic diarrhea, particularly if the diarrhea is watery, occurs frequently (more than 3 loose stools per day), and has persisted for more than 4 weeks without a clear cause. The test is especially valuable when other conditions like inflammatory bowel disease, celiac disease, and infections have been ruled out.
Common reasons for ordering this test include unexplained chronic diarrhea, suspected IBS-D that hasn't responded to standard treatments, diarrhea following gallbladder removal (cholecystectomy), diarrhea after ileal resection or Crohn's disease affecting the terminal ileum, and evaluation of patients with microscopic colitis or radiation enteritis.
Studies show that up to 50% of patients who have had their gallbladder removed (cholecystectomy) may develop some degree of bile acid malabsorption. This is because without a gallbladder, bile flows continuously into the intestine rather than being stored and released with meals, which can overwhelm the intestine's absorption capacity.
How Should I Prepare for the Test?
Preparation for the SeHCAT test includes fasting from midnight before your first appointment, stopping certain medications as directed by your doctor, and informing your healthcare team if you are pregnant, breastfeeding, or might be pregnant. No special preparation is needed for the second appointment.
Proper preparation is essential for accurate test results. The SeHCAT test is conducted over two separate appointments, typically scheduled exactly 7 days apart. Each appointment has different preparation requirements, and understanding these requirements will help ensure your test provides reliable diagnostic information.
Before Your First Appointment
The night before your first appointment, you must stop eating and drinking at midnight. This overnight fast is necessary because food in your digestive system can interfere with the initial measurement of the radioactive tracer. You may take essential medications with small sips of water, but check with your healthcare provider about specific medications.
Several types of medications may need to be paused before and during the test period to ensure accurate results. Your healthcare provider will give you specific instructions, but commonly affected medications include:
- Bile acid sequestrants (such as cholestyramine, colesevelam, or colestipol) – these medications bind bile acids and will artificially improve your test results, masking the true extent of malabsorption
- Opioid-based pain medications – these slow gut motility and can affect bile acid absorption
- Anti-diarrheal medications containing loperamide (Imodium) – these affect intestinal transit time
- Proton pump inhibitors – may be continued unless otherwise directed
The timing of when to stop these medications varies. Bile acid sequestrants typically need to be stopped 2-4 weeks before the test, while loperamide may only need to be stopped a few days prior. Always follow your doctor's specific instructions, as stopping medications inappropriately could affect other aspects of your health.
Before Your Second Appointment
No special preparation is required before your second appointment. You can eat and drink normally and continue your regular activities. However, you should continue to avoid any medications that were restricted during the testing period until after your second scan is complete.
The SeHCAT test uses radioactive material and is not recommended during pregnancy or breastfeeding. If you are pregnant, suspect you might be pregnant, or are breastfeeding, inform your healthcare provider immediately. Alternative diagnostic approaches, such as a therapeutic trial of bile acid sequestrants, may be considered instead.
How Does the Test Work?
The SeHCAT test involves swallowing a capsule containing a radioactive tracer, waiting one hour, then having a gamma camera scan. After 7 days, you return for a second scan. The difference between the two scans shows how much bile acid your body has retained, indicating whether malabsorption is present.
Understanding the test procedure can help reduce anxiety and ensure you're fully prepared for each appointment. The SeHCAT test is painless, non-invasive, and typically well-tolerated by patients. Here's a detailed breakdown of what to expect at each stage of the testing process.
First Appointment (Day 1)
When you arrive at the nuclear medicine department, a healthcare professional will explain the procedure and answer any questions you may have. You'll be asked to confirm that you've followed the fasting instructions and whether you've stopped the required medications.
The test begins when you swallow a SeHCAT capsule with a small amount of water. This capsule contains selenium-75-labeled homocholic acid taurine, a synthetic bile acid that mimics natural bile acid behavior. The capsule is similar in size to a standard vitamin pill and is easy to swallow. The radiation dose is very low – approximately equivalent to a single chest X-ray.
After swallowing the capsule, you'll wait approximately one hour. During this time, the tracer is absorbed into your enterohepatic circulation and distributed throughout your body. You can sit comfortably in the waiting area during this period.
Following the waiting period, you'll lie on a scanning bed while a gamma camera is positioned over your abdomen. The camera detects the radiation emitted by the selenium-75 and creates an image showing the distribution of the tracer. This baseline scan takes approximately 10-15 minutes and is completely painless – the camera does not emit any radiation and simply records what's already in your body.
After the scan, you can resume your normal diet and activities. There are no dietary restrictions during the 7-day waiting period, and you won't notice any effects from the radioactive tracer. The radiation exposure is minimal and poses no significant health risk.
Second Appointment (Day 7)
Exactly 7 days after your first scan, you'll return to the nuclear medicine department for a follow-up scan. This appointment is shorter, typically taking only about 30 minutes. No fasting or special preparation is required.
The same gamma camera technique is used to measure how much of the radioactive tracer remains in your body. In a person with normal bile acid absorption, most of the tracer will have been retained and recycled multiple times through the enterohepatic circulation. In someone with bile acid malabsorption, a significant portion of the tracer will have been lost through the stool.
After the second scan, you can return to your normal activities immediately. Your healthcare provider will analyze the results by comparing the amount of tracer detected on day 7 to the amount detected on day 1. This comparison, expressed as a percentage, provides a clear measure of your bile acid retention.
| Stage | What Happens | Duration | Preparation |
|---|---|---|---|
| Day 1 - Arrival | Check-in, medical history review, capsule ingestion | 15-20 minutes | Fast from midnight, stop specified medications |
| Day 1 - Wait | Tracer absorption and distribution in body | ~1 hour | Remain in waiting area |
| Day 1 - Baseline Scan | Gamma camera imaging of abdomen | 10-15 minutes | Lie still on scanning bed |
| Day 7 - Follow-up Scan | Second gamma camera imaging, retention calculation | 30 minutes total | No special preparation needed |
How Will I Feel After the Test?
Most people feel completely normal after the SeHCAT test with no side effects. The radioactive tracer does not cause any symptoms, and you can resume all normal activities including work, exercise, and social activities immediately after each appointment.
One of the significant advantages of the SeHCAT test is that it causes no physical discomfort or side effects for the vast majority of patients. Unlike some medical tests that may cause fatigue, nausea, or require recovery time, the SeHCAT scan allows you to continue with your daily routine immediately.
The radioactive selenium-75 used in the test emits very low levels of radiation and is gradually eliminated from your body naturally over the following weeks. The radiation exposure from a complete SeHCAT test (both scans combined) is approximately 0.3 millisieverts (mSv), which is less than the radiation from a standard CT scan and roughly equivalent to 6 weeks of natural background radiation.
You don't need to take any special precautions around others, including children or pregnant women, as the radiation levels are extremely low. There are no restrictions on physical contact, sharing bathrooms, or any other daily activities. The radioactive material is excreted naturally and safely through your digestive system.
When to Contact Your Healthcare Provider
While complications from the SeHCAT test are extremely rare, you should contact your healthcare provider if you experience any unexpected symptoms such as severe abdominal pain, difficulty swallowing the capsule, or any signs of allergic reaction (extremely rare). These symptoms are not typically related to the test itself but should be evaluated to rule out other conditions.
What Do the Results Mean?
SeHCAT results show the percentage of bile acid retained after 7 days. Normal retention is above 15%. Mild bile acid malabsorption is 10-15% retention, moderate is 5-10%, and severe is less than 5% retention. Lower percentages indicate more severe malabsorption and typically correlate with worse symptoms.
Understanding your SeHCAT results is crucial for determining the appropriate treatment approach. The test measures what percentage of the radioactive tracer remains in your body after 7 days, which directly reflects your body's ability to absorb and retain bile acids. This retention value provides valuable information about both the diagnosis and severity of bile acid malabsorption.
In healthy individuals with normal bile acid absorption, the 7-day retention is typically greater than 15%. This means that more than 15% of the original tracer remains in the enterohepatic circulation, being continuously recycled between the intestine and liver. When retention falls below this threshold, it indicates that bile acids are being lost through the stool rather than being efficiently recycled.
| 7-Day Retention | Classification | Clinical Significance | Typical Treatment Response |
|---|---|---|---|
| >15% | Normal | Bile acid absorption is normal; other causes of diarrhea should be investigated | Unlikely to respond to bile acid sequestrants |
| 10-15% | Mild BAM | Modest excess bile acids reaching the colon; may contribute to symptoms | About 80% respond to low-dose bile acid sequestrants |
| 5-10% | Moderate BAM | Significant bile acid loss; likely a major cause of symptoms | About 90% respond to bile acid sequestrants |
| <5% | Severe BAM | Substantial bile acid malabsorption; primary cause of diarrhea | Over 95% respond to bile acid sequestrants |
The correlation between SeHCAT retention values and treatment response is well established in clinical research. Studies have shown that patients with lower retention values (indicating more severe malabsorption) tend to have more pronounced symptoms and typically experience the most dramatic improvement with bile acid sequestrant therapy.
Receiving Your Results
Your test results will be analyzed by the nuclear medicine team and sent to the referring physician who ordered the test. You can typically expect to receive your results within a few weeks of completing the second scan. Your doctor will contact you to discuss the findings and, if bile acid malabsorption is confirmed, to discuss treatment options.
If your results show bile acid malabsorption, your doctor will likely recommend treatment with bile acid sequestrants such as cholestyramine, colesevelam, or colestipol. These medications bind bile acids in the intestine, preventing them from causing diarrhea. Many patients experience significant improvement in their symptoms within days to weeks of starting treatment.
Clinical studies show that approximately 70-96% of patients with confirmed bile acid malabsorption respond well to bile acid sequestrant therapy. The severity of malabsorption (as measured by SeHCAT retention) often predicts treatment response, with more severe cases typically showing more dramatic improvement.
Is the Test Safe?
Yes, the SeHCAT test is very safe. The radiation dose is very low (about 0.3 mSv total), comparable to a few chest X-rays. The main contraindication is pregnancy and breastfeeding. The test has been used safely for over 40 years with no significant adverse effects reported.
Safety is a common concern for patients undergoing any nuclear medicine procedure. The SeHCAT test has an excellent safety record spanning more than four decades of clinical use, and understanding the safety profile can help alleviate any concerns you may have.
The radiation exposure from the SeHCAT test is minimal. The total effective dose from both scans combined is approximately 0.3 millisieverts (mSv). To put this in perspective, the average person receives about 3 mSv per year from natural background radiation sources like cosmic rays and radon in the soil. A single CT scan of the abdomen delivers approximately 10 mSv – more than 30 times the radiation from a SeHCAT test.
The selenium-75 tracer used in the test is eliminated from your body naturally over time. It does not accumulate in any organs or tissues, and there are no long-term effects from the radiation exposure. The tracer is chemically identical to natural bile acids and is processed by your body in exactly the same way, making it inherently safe.
Who Should Not Have This Test?
While the SeHCAT test is safe for most people, there are specific situations where it should be avoided or postponed:
- Pregnancy: The test should not be performed during pregnancy due to the potential radiation exposure to the developing fetus. If you are pregnant or suspect you might be pregnant, inform your healthcare provider immediately.
- Breastfeeding: While the radiation levels are low, women who are breastfeeding should discuss the timing of the test with their healthcare provider. Temporary interruption of breastfeeding may be recommended.
- Recent nuclear medicine tests: If you've recently had another nuclear medicine scan, your doctor may recommend waiting before performing the SeHCAT test to avoid interference between tracers.
There are no known allergies to the SeHCAT capsule, and serious adverse reactions have not been reported in the medical literature. The test does not require any sedation, contrast dyes, or invasive procedures, further contributing to its excellent safety profile.
Are There Alternative Tests?
While SeHCAT is the gold standard, alternatives include therapeutic trial of bile acid sequestrants (most common when SeHCAT unavailable), serum 7α-hydroxy-4-cholesten-3-one (C4) blood test, and fecal bile acid measurement. The therapeutic trial is widely used but less specific than SeHCAT.
Although the SeHCAT test is considered the gold standard for diagnosing bile acid malabsorption, it is not available in all countries or healthcare facilities. In the United States, for example, the SeHCAT test is not FDA-approved, and alternative diagnostic approaches are commonly used. Understanding these alternatives can help you discuss options with your healthcare provider.
Therapeutic Trial
The most widely used alternative to SeHCAT testing is a therapeutic trial of bile acid sequestrants. In this approach, patients are given a bile acid sequestrant medication (such as cholestyramine) for a trial period of 2-4 weeks. If symptoms improve significantly, this strongly suggests bile acid malabsorption was the underlying cause.
While practical and widely accessible, the therapeutic trial approach has limitations. It cannot quantify the severity of malabsorption, some patients may have partial responses for other reasons, and the medications can cause side effects like constipation and bloating that may affect compliance.
Serum C4 Test
The serum 7α-hydroxy-4-cholesten-3-one (C4) blood test measures a bile acid precursor in the blood. When bile acid malabsorption occurs, the liver increases bile acid synthesis to replace the lost acids, and C4 levels rise accordingly. This test requires only a blood draw and results are typically available within a few days.
However, the C4 test has some limitations. C4 levels show significant daily variation and are affected by food intake, so fasting samples are required. The test is also less well-standardized than SeHCAT, and reference ranges may vary between laboratories. Some conditions affecting liver function can also influence results.
Fecal Bile Acid Measurement
Direct measurement of bile acids in stool samples can confirm increased bile acid excretion. This test requires collection of stool over a 48-72 hour period, which some patients find inconvenient. Laboratory availability and standardization also vary widely.
What Causes Bile Acid Malabsorption?
Bile acid malabsorption has three main types: Type 1 occurs after ileal resection or in Crohn's disease; Type 2 is primary/idiopathic with no clear cause; Type 3 is secondary to other conditions like cholecystectomy, celiac disease, or diabetes. Type 2 is most common, affecting up to 30% of IBS-D patients.
Understanding the underlying cause of bile acid malabsorption is important for treatment planning and prognosis. Clinicians classify bile acid malabsorption into three main types based on the underlying mechanism, and knowing which type you have can help guide long-term management.
Type 1: Ileal Dysfunction
Type 1 bile acid malabsorption occurs when the terminal ileum – the last section of the small intestine where bile acid absorption normally occurs – is damaged, diseased, or surgically removed. This type has a clear structural or anatomical cause.
Common causes of Type 1 bile acid malabsorption include surgical resection of the terminal ileum (often for Crohn's disease or cancer), active Crohn's disease affecting the terminal ileum, radiation enteritis following pelvic radiotherapy, and ileal bypass surgery (historical weight loss procedure).
Patients with Type 1 malabsorption typically have a known medical history that explains their condition. Treatment is usually lifelong, as the underlying structural problem cannot be reversed.
Type 2: Primary/Idiopathic
Type 2 bile acid malabsorption, also called primary or idiopathic bile acid malabsorption, occurs in patients with no obvious intestinal disease or surgery. This is the most common type and is increasingly recognized as a major cause of chronic diarrhea.
Research suggests that Type 2 malabsorption may be related to reduced production of fibroblast growth factor 19 (FGF19), a hormone that normally signals the liver to reduce bile acid production. Without adequate FGF19, the liver overproduces bile acids, overwhelming the intestine's absorption capacity.
Type 2 is particularly important in patients with diarrhea-predominant irritable bowel syndrome (IBS-D). Studies suggest that 25-33% of patients diagnosed with IBS-D actually have unrecognized bile acid malabsorption as the primary cause of their symptoms.
Type 3: Secondary
Type 3 bile acid malabsorption occurs secondary to other gastrointestinal conditions or surgeries that indirectly affect bile acid absorption. Unlike Type 1, the terminal ileum itself is intact.
Common causes of Type 3 malabsorption include cholecystectomy (gallbladder removal), which affects bile storage and release timing, celiac disease causing general malabsorption, small intestinal bacterial overgrowth (SIBO), chronic pancreatitis, diabetic autonomic neuropathy affecting gut motility, and microscopic colitis.
Post-cholecystectomy diarrhea is particularly common, affecting up to 10-20% of patients following gallbladder surgery. In many cases, bile acid malabsorption is the underlying cause and responds well to bile acid sequestrant therapy.
How Can I Participate in My Care?
Active participation in your care includes understanding your test results, asking questions about treatment options, keeping a symptom diary before and after treatment, and communicating openly with your healthcare team about medication side effects or concerns. Informed patients typically achieve better outcomes.
Being an active participant in your healthcare journey can significantly improve your outcomes and quality of life. When dealing with bile acid malabsorption testing and treatment, there are several ways you can take an active role in your care.
Understanding Your Condition
Taking time to understand bile acid malabsorption and its causes will help you make informed decisions about your care. Don't hesitate to ask your healthcare provider to explain test results, treatment options, and what you can expect from therapy. Understanding why certain medications work and what side effects to watch for will help you manage your condition effectively.
Tracking Your Symptoms
Keeping a symptom diary can provide valuable information for your healthcare team. Record the frequency and consistency of your bowel movements, any foods that seem to trigger or worsen symptoms, the timing of symptoms in relation to meals, and how symptoms change after starting treatment.
Communicating About Treatment
If you're prescribed bile acid sequestrants, be prepared to discuss your experience openly with your healthcare provider. These medications can cause side effects like constipation, bloating, and interference with other medications. If you're having difficulty tolerating the medication, your doctor may adjust the dose or recommend a different formulation.
- What do my test results mean, and how severe is my bile acid malabsorption?
- What treatment options are available, and which do you recommend?
- Are there any dietary changes that might help manage my symptoms?
- How soon can I expect to see improvement with treatment?
- Will I need to take medication long-term?
- Are there any potential interactions with my other medications?
Frequently Asked Questions About Bile Acid Malabsorption Testing
Medical References and Sources
This article is based on current medical research and international guidelines. All claims are supported by scientific evidence from peer-reviewed sources.
- British Society of Gastroenterology (BSG) (2020). "Guidelines on the investigation of chronic diarrhoea in adults." Gut Journal Evidence-based guidelines for investigating chronic diarrhea including bile acid malabsorption testing.
- National Institute for Health and Care Excellence (NICE) (2023). "Irritable bowel syndrome in adults: diagnosis and management." NICE Guideline CG61 Clinical guidelines including investigation of IBS-D and bile acid malabsorption.
- Walters JRF, et al. (2020). "A systematic review and meta-analysis of bile acid malabsorption in IBS-D." Alimentary Pharmacology & Therapeutics. Comprehensive review of bile acid malabsorption prevalence and diagnosis. Evidence level: 1A
- Wedlake L, et al. (2009). "Systematic review: the prevalence of idiopathic bile acid malabsorption as diagnosed by SeHCAT scanning in patients with diarrhoea-predominant IBS." Alimentary Pharmacology & Therapeutics. 30(7):707-17. Key study establishing prevalence of bile acid malabsorption in IBS-D patients.
- Vijayvargiya P, et al. (2018). "Methods for diagnosis of bile acid malabsorption in clinical practice." Clinical Gastroenterology and Hepatology. 16(9):1426-1432. Comparative review of diagnostic methods including SeHCAT, C4, and therapeutic trials.
- Mottacki N, et al. (2016). "Review article: bile acid diarrhoea - pathogenesis, diagnosis and management." Alimentary Pharmacology & Therapeutics. 43(8):884-98. Comprehensive review of bile acid diarrhea pathophysiology and clinical management.
Evidence grading: This article uses the GRADE framework (Grading of Recommendations Assessment, Development and Evaluation) for evidence-based medicine. Evidence level 1A represents the highest quality of evidence, based on systematic reviews of randomized controlled trials.
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