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Normally, the liver is very efficient at capturing and removing bile acids from the hepatic-portal circulation. This is why circulating bile acid levels are quite low in healthy animals. The liver has tremendous reserve capacity and can easily meet the body's demand for bile acids despite severe disease. As a result of this reserve, the bile acid levels do not typically drop due to liver disease, therefore, as liver function is compromised, more bile acids appear in the blood. The test for serum bile acids will detect liver changes before the formation of more advanced clinical signs of illness such as icterus. This early sensitivity is very important to the practitioner because it allows for the possibility of treatment before extensive and irreversible damage is done. It is important to distinguish between the information provided by liver enzymes such as ALT and bile acids. Alanine aminotransferase is an enzyme released from damaged liver cells and, therefore, an indicator of hepatocellular integrity. Bile acids are indicators of a liver function. However, the test will not provide a definitive diagnosis of the primary problem, merely an early confirmation that there is a hepatobiliary deficiency. Therefore, once an animal becomes jaundiced, the benefits of the test decline unless used to monitor response to treatment. Indications There is a wide range of symptoms that make a patient a candidate for this test. Some of these are anorexia, vomiting, lethargy, weight loss, fever, hepatomegley, inhibited growth, long anesthesia recovery, ascities, abnormal stool and hepatic encephelopathy (disorientation, hypersalavation, aggression, ataxia or seizures that can all be affected by meals). There are a large number of diseases that can compromise hepatobiliary function in a primary or secondary manner. Liver diseases that can elevate values include hepatic neoplasia, portosystemic shunt, hepatic lipidosis, hepatitis, feline infectious peritonitis, bile duct obstruction, canine adenovirus, slowed gastrointestinal transit, copper toxicity and almost any condition that causes a defect in hepatic uptake or portal circulation. Test results that appear low are usually due to normal variation or prolonged fasting, but can also indicate intestinal malabsorption or increased gastric motility. Normally, a small increase will be seen from the fasted to the post-prandial sample, however hepatobiliary disorders can cause elevated fasting and/or elevated post-prandial values. Although the bile acids test does not provide a definitive diagnosis, the relationship of the fasting and post-prandial samples do suggest certain disorders as seen in the chart below. |
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