Bile Acids Testing
A well-known hepatologist once said that if a room were empty, a bile acids meeting must be taking place. If you were to ask a hepatologist, they would tell you there is nothing exciting about bile acids. However, if you asked a member of the veterinary community, you would get a completely different answer.
Patients with impaired bile acids clearance can present with a multitude of striking clinical signs involving the nervous, gastrointestinal and urinary systems. These signs are a reflection of bile acids’ important role in healthy functioning. Bile acids emulsify fatsoluble vitamins and cholesterol. Recently, we have also learned that bile acids act as signaling hormones, helping out with metabolic actions.
An effective enterohepatic system ensures that only very small quantities of bile acids enter the systemic blood stream. In a normal patient, these detergent-like substances are made in the liver, stored in the gallbladder, and secreted into the small intestine. The enterohepatic transport system reabsorbs bile acids and returns them via the portal vein to the liver, which saves them to be used again. In a healthy fasting patient, little enterohepatic circulation is needed, causing bile acids in circulation to be minute. In a healthy non-fasting patient, the gallbladder contracts and releases bile acids. As a result, a slightly higher concentration of bile acids is present in plasma.
A patient with an impaired enterohepatic system can have an abnormally high concentration of bile acids in systemic circulation. Bile acids testing can detect these high levels, giving the clinician a picture of hepatobiliary function. Patients presenting with signs of portosystemic shunting (PSS), ammonium biurate crystalluria or urolithiasis, or cholestasis because of cirrhosis benefit from testing. Even in severe cirrhotic disease, patients might have normal or almost normal liver values; bile acids are more sensitive than a routine chemistry panel.
Reliable and cost-effective in-house testing is available, making initial testing and later follow-up available on demand. This is imperative because sequential monthly monitoring is necessary in cirrhotic cases, and congenital PSS patients need post-operative follow-up testing. In other hepatobiliary cases, bile acids’ usefulness is limited, as its sensitivity is lower. In situations when hyperbilirubinemia is present, testing is not indicated, as bile acid levels will always be abnormal.
Since testing is indicated in many cases, knowing the procedure is useful. Bile acid secretion is stimulated by food ingestion, hence a blood sample must be taken after a 12-hour fast. A small meal (10- 30 millilitres, depending on the size of the patient) is offered so that the gallbladder contracts. Two hours after the meal, a second sample is obtained. Samples should be free of hemolysis and lipemia, as these interferences can affect result accuracy. Increased bile acids have been identified in healthy Maltese dogs and patients with gastrointestinal disease, thus the results should be interpreted judiciously.
As the evidence shows, for certain patient populations, bile acid test results are very revealing. Hepatologists are discovering that bile acids have more of a role in medicine than previously thought. The next time a bile acids meeting takes place, the room might not be so empty.