Bile acids are synthesised in the liver as end-products of cholesterol metabolism. Together with other components of the liver bile, such as cholesterol, bilirubin, phospholipids and proteins, bile acids are secreted into the duodenum.
Important functions of bile acids include the excretion of cholesterol, absorption of fatty acids and fat-soluble vitamins in the small intestine as well as the stimulation of intestinal motility.
The majority of the secreted bile acids are reabsorbed in the terminal ileum and returned to the liver via enterohepatic circulation. Only a small proportion (3-5%) of bile acids are excreted into the faeces.
If the enterohepatic recycling of bile acids fails, excess amounts of bile acids enter the colon and are lost with the faeces; this condition is called bile acid malabsorption and is caused by several clinical situations:
Post terminal ileum resection
Crohn‘s Disease in the terminal ileum
Faecal bile acids may provide a non-invasive and safe method to support the diagnosis of all types of bile acid malabsorption. Bile acid malabsorption or bile acid diarrhoea is thought to affect up to one third of individuals who suffer from diarrhoea predominant IBS. Although there are several treatment options available, these rely upon a diagnosis being made and the current technique for this is referral for a Tauroselcholic [??Se] Acid (SeHCAT) test - a two stage procedure carried out by nuclear medicine. The SeHCAT test involves the ingestion of a capsule containing synthetic bile salts labelled with a slightly radioactive tracer, followed by two gamma camera scans one week apart. This specialist test is not routinely available in all localities and so a faecal bile acid test may serve as a useful patient selection tool for referral.