SeHCAT (tauroselcholic (75 selenium) acid) as a test for diagnosing bile acid malabsorption

SeHCAT (tauroselcholic (75selenium) acid) is a potentially clinically important test for diagnosing bile acid malabsorption

• SeHCAT
  • is a radiopharmaceutical that is licensed for use in measuring bile acid pool loss and investigating bile acid malabsorption. It can also be used in the assessment of ileal function, to investigate inflammatory bowel disease (IBD) and chronic diarrhoea, and to study enterohepatic circulation
    
    
  • consists of a capsule containing a synthetic analogue of the natural conjugated bile acid tauroselcholic acid and 75Selenium (a gamma-emitter)
    • radionuclide tracer atom allows SeHCAT to be easily detected in a whole body scan using a standard gamma camera. The technology is used to test the function of the bowel by measuring how well the compound is retained or lost from the body into the faeces. SeHCAT is the only test currently used to diagnose bile acid malabsorption
      
      
  • SeHCAT test involves 2 scans, 1 week apart, carried out as outpatient appointments
    • during the first appointment, the SeHCAT capsule is administered orally and, once localised in the body (which takes 1-3 hours), the radionuclide tracer atom is detected in a whole-body baseline scan using a standard gamma camera. This gives an initial count that is used to provide a zero-time or 100% value
    • during the second appointment, the patient is scanned to produce a second count, and the retained activity is expressed as a percentage of the original value. In general practice, retention values of less than 15% have been considered abnormal and indicative of bile acid malabsorption. However, there is no definitive cut-off between normal and abnormal
      
    • although the models used in the assessment assumed no treatment differences based on the results of tests using SeHCAT, clinicians have used SeHCAT results to grade the severity of the bile acid malabsorption as follows:
      • retention values of 10-15% (mild bile acid malabsorption)
      • retention values of 5-10% (moderate bile acid malabsorption)
      • retention values of 0-5% (severe bile acid malabsorption).

NICE concluded that (1) there is insufficient evidence to determine whether SeHCAT is a cost-effective option for diagnosing bile acid malabsorption in people with diarrhoea-predominant irritable bowel syndrome (IBS-D) and people with Crohn's disease without ileal resection

Reference:

1. NICE. SeHCAT (tauroselcholic [75 selenium] acid) for diagnosing bile acid diarrhoea. Diagnostics guidance DG44 published November 2021