Bile acids are compounds the liver produces to assist with the digestion of dietary fats. Two common examples are chenodeoxycholic and cholic acid. The acids move from the liver to the gallbladder, which concentrates them before releasing them into the intestines after eating. Their levels in the body can vary depending on health and when someone has last eaten, and a doctor may request a test to check for them if there are concerns about a patient's liver, gallbladder, or digestive health.
The liver uses cholesterol as the source for bile acids, treating cholesterol with enzymes to break it down into usable components. After synthesis in the liver, they travel down the bile duct and into the gallbladder, where they wait until the body needs them. When people eat and the meal contains dietary fats, they signal the gallbladder to release some bile to assist with digestion. The bile acids travel through the intestines, and the vast majority is reabsorbed into the circulation, where the acids work their way back into the liver for recycling.
In addition to processing dietary fats, bile acids can also bind to waste materials in the body. When these bile acids move through the digestive tract, instead of being returned to circulation, they are expressed in the feces. Compounds like bilirubin rely on this method for transport out of the body.
These compounds can cause cellular damage if their concentrations get too high. High levels of bile acids will trigger inhibitor molecules to tell the liver to stop production until the body actually needs more. The body relies on feedback from the intestines, liver, and gallbladder to keep bile acids at a safe and reasonable level. Any errors with this process can cause problems for a patient.
Patients may have unusually high or low bile acids because of issues like liver dysfunction, problems with the hepatic portal vein, or gallbladder disease. The testing can provide information about the concentrations when fasting and after eating so the doctor has a complete picture of what is happening inside the patient. Doctors may also request testing on liver enzyme levels to see if the patient's liver is functioning normally. If the patient appears to have a problem, additional testing like abdominal ultrasound can provide more information, as can a patient interview to check for symptoms like abdominal pain. The patient can also provide information about her diet, which can offer useful diagnostic clues.