Bile acids are chemical compounds made from cholesterol in the liver. Their primary role is to help digest and absorb fats and fat-soluble vitamins, but they also act as signaling molecules that influence cholesterol balance, gut microbiome composition, and even blood sugar regulation. Measuring total bile acids gives an overall sense of how much is circulating in the blood, while measuring specific bile acids, like cholic acid, deoxycholic acid, and chenodeoxycholic acid, helps reveal the balance between different bile acid pathways.
Cholic acid and chenodeoxycholic acid are called primary bile acids. They are produced directly by the liver and represent the starting point of bile acid metabolism. When these acids reach the intestine, gut bacteria transform them into secondary bile acids, such as deoxycholic acid. This interplay between the liver and gut is known as the enterohepatic circulation. If liver function is impaired, if bile ducts are blocked, or if the intestine’s microbial balance is disturbed, this recycling system can break down, leading to abnormal levels in the blood.
When levels of total bile acids rise, it usually means that bile cannot flow freely out of the liver, a condition called cholestasis. This is seen in liver diseases such as hepatitis and cirrhosis, as well as in gallstone obstruction and in intrahepatic cholestasis of pregnancy, a pregnancy complication marked by itching and fetal risk.
Abnormalities in these individual bile acids can also appear before standard liver enzyme tests (such as ALT and AST) show changes, making fractionated bile acid testing a more sensitive tool in some cases. However, interpretation is nuanced. For example, fasting versus post-meal testing produces different results, since bile acids naturally surge after eating. Diet, medications, and the gut microbiome also affect bile acid composition. Thus, the test is best interpreted in the broader context of liver function tests, imaging, and clinical symptoms.
