Abnormal liver enzymes are often seen in small animal patients. Sometimes these abnormalities are seen during routine health screens in asymptomatic animals; on other occasions, the patient is sick and has abnormal liver enzyme values. Reactive hepatopathies secondary to a primary nonhepatic disorder must be differentiated from primary liver disease. Reactive hepatopathies are caused by neoplasia as well as gastrointestinal, renal, autoimmune, dermatologic, dental, infectious, and cardiac diseases. These are the most common causes of elevated liver enzymes. In most of these cases, alanine transaminase, aspartate transaminase, alanine phosphatase, and γ-glutamyl transaminase are elevated, but bilirubin, albumin, glucose, blood urea nitrogen, and bile acids are normal.

Other causes of enzyme elevations are vacuolar hepatopathies. Steroid hepatopathies can be seen in dogs secondary to exogenous or endogenous glucocorticoid administration. There are usually marked increases in alanine phosphatase. Idiopathic vacuolar hepatopathy is seen in older dogs with elevated alanine phosphatase that have no clinical or laboratory indications of Cushing's disease. Some of these dogs may have elevations of other adrenal steroids, such as progesterone or estradiol. Nodular hyperplasia is another relatively benign liver process that can cause an elevation in liver enzymes. In one study, these nodules were present in all dogs older than 14 years.

COMMENTARY: Recognition of the extrahepatic causes of liver enzyme abnormalities will help in the appropriate management of the patient for the disease process that is present.

The most common liver diseases in the dog. Twedt DC. ACVIM PROCEEDINGS, 2003, pp 267-269.