Measurement of stool bile acids aids in evaluating patients suspected of having chronic diarrhea symptoms due to bile acid malabsorption. Stool bile acids are essential to digestive health and can provide insights into gastrointestinal conditions. Bile acids are produced by the liver and released into the small intestine to aid in the digestion and absorption of fats. They play a crucial role in emulsifying fats and fat-soluble vitamins, facilitating their absorption.
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Bile acids are produced 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. Essential functions of bile acids are the excretion of cholesterol, absorption of fatty acids and fat-soluble vitamins in the small intestine, such as A, D, E, and K, and stimulation of intestinal motility.
Bile acid synthesis and excretion are tightly regulated processes. They are primarily synthesized from cholesterol in the liver and stored in the gallbladder. After a meal, bile is released into the small intestine to aid digestion. The majority of the secreted bile acids are reabsorbed in the terminal ileum and returned to the liver via the portal venous system for eventual recirculation in a process known as enterohepatic circulation; only a small proportion (3-5%) is excreted into the feces. If the enterohepatic recycling of bile acids fails, excess amounts enter the colon and are lost in the feces; this condition is called bile acid malabsorption. Primary bile acids cholic acid (CA) and chenodeoxycholic acid (CDCA) are deconjugated and dehydroxylated via intestinal bacteria into secondary bile acids deoxycholic acid (DCA) and lithocholic acid (LCA), respectively. The sum of CA, CDCA, DCA, LCA, and ursodeoxycholic acid composes most bile acids in the feces.
Abnormal levels of stool bile acids can indicate various gastrointestinal disorders. Increased levels may suggest malabsorption syndromes, such as bile acid malabsorption (BAM), which can lead to diarrhea and other digestive symptoms. Reduced levels may indicate impaired bile acid synthesis or excretion, which can occur in conditions like cholestasis or liver disease.
Indications for the measurement of bile acids in the stool are:
- Suspected bile acid malabsorption
- After resection of the terminal ileum
- Crohn‘s Disease affecting the terminal ileum
- Radiation enteritis
- Post-cholecystectomy
- Post-vagotomy
- Celiac disease
- Chronic pancreatitis
- Idiopathic bile acid malabsorption
Treatment: Treatment for abnormal stool bile acids may include dietary modifications, medications to bind bile acids and reduce their circulation, and addressing underlying causes such as liver or gastrointestinal diseases.
This test can help diagnose abnormal bile acid metabolism conditions, such as BAM. Additionally, serum bile acid tests may be performed to assess liver function and diagnose liver diseases.
