Review on bile acid analysis

Bile acids are made in the liver by the cytochrome P450-mediated oxidation of cholesterol. They are conjugated with taurine or the amino acid glycine, or with a sulfate or a glucuronide, and are then stored in the gallbladder, which concentrates the salts by removing the water. Bile acids serve other functions, including eliminating cholesterol from the body, driving the flow of bile to eliminate catabolites from the liver, emulsifying lipids and fat-soluble vitamins in the intestine to form micelles that can be transported via the lacteal system, and aiding in the reduction of the bacteria flora found in the small intestine and biliary tract. Conjugated bile acids are more efficient at emulsifying fats because, at intestinal pH, they are more ionized than unconjugated bile acids. Several assays have been used to determine both total and individual bile acids in biological fluids. The methods that have been used specifically to analyze serum TBA (total Bile Acid) are gas-liquid chromatography (GLC), High Performance Liquid Chromatography (HPLC), enzymatic assays and enzyme cycling assays. GLC and HPLC methods are not commonly used in clinical laboratories where automated clinical chemistry analyzers are used for most of chemistry tests including TBA testing. The enzymatic assay is now mainly used in small laboratories where TBA test are in lyophilized powder form and manual reconstitution steps are needed before use. At present, the most widely used TBA test in clinical laboratories is the enzyme cycling method. That is a liquid-stable assay and ready to use for all types of automated chemistry analyzers.