Bile Acids

The bile acid test (also known as the bile salt test) assesses the integrity of enterohepatic circulation across hepatocytes, the biliary tree, intestinal absorption, and portal venous return. Measuring total bile acids aids the diagnosis of cholestasis as part of liver function assessment, including intrahepatic cholestasis of pregnancy. In conjunction with routine liver chemistries, total bile acids assist in evaluating the activity of liver disease in diverse settings, including chronic viral hepatitis and cholestatic disorders.

Bile acids are synthesized from cholesterol in hepatocytes, concentrated in the gallbladder, and released into the duodenum to facilitate emulsification and absorption of dietary lipids. Approximately 90% are reclaimed in the intestine and return to the liver through the portal vein, maintaining the enterohepatic pool and contributing to gut microbiome homeostasis. When bile formation or flow is impaired (cholestasis), bile acids accumulate in the bloodstream. Clinical manifestations can include pruritus that is often worse at night, jaundice, and fatigue. Cholestasis may be extrahepatic, as with ductal obstruction by stones or tumors, or intrahepatic due to hepatocellular or ductular disease. Reported causes include mechanical obstruction; hepatocellular dysfunction such as hepatitis or cirrhosis; genetic cholestatic syndromes (benign recurrent intrahepatic cholestasis, progressive familial intrahepatic cholestasis, ABCB4 deficiency, erythropoietic protoporphyria); biliary malformations (biliary hamartomas, Caroli syndrome); and parasitic infections (opisthorchiasis, fascioliasis, ascariasis, clonorchiasis, echinococcosis). Among laboratory measures for intrahepatic cholestasis of pregnancy, serum total bile acids are among the most sensitive; fasting concentrations ≥40 µmol/L have been associated with increased risks of preterm delivery and adverse perinatal outcomes. In this context, aminotransferase activities may be normal or only mildly elevated, while alkaline phosphatase is usually increased, although interpretation in pregnancy is limited by placental isoenzyme production.