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29 MAY/JUNE ■ TVPJOURNAL.COM CONTINUING EDUCATION Liver Enzyme Interpretation and Liver Function Tests Brigitte B. McAtee, DVM Jonathan A. Lidbury, BVMS, MRCVS, PhD, DACVIM, DECVIM-CA Texas A&M; University Hepatobiliary disease is an important cause of morbidity and mortality in dogs and cats and can present a diagnostic challenge for two main reasons. First, patient signalment varies because liver disease and dysfunction can occur in cats and dogs of any age, sex, or breed (see Case Studies ). Despite this, the patient's signalment can sometimes give important clues because certain breeds have disease predispositions; for example, Labrador retrievers are predisposed to copper-associated chronic hepatitis. Second, elevations of serum liver enzyme activities are commonly encountered in small animal practice but are not specific for primary liver disease. However, early in the course of liver diseases, such as chronic hepatitis, patients may have no or only subtle, nonspecific clinical signs, such as intermittent anorexia or lethargy. In these patients, increased liver enzyme activities may be the first indicator of a problem. More liver-specific clinical signs, such as icterus, ascites, edema, polyuria/ polydipsia, and hepatic encephalopathy, tend to occur late in the course of disease, when it is often too late to prevent its progression. Therefore, early diagnosis of liver disease often relies on serum biochemical testing, which may prompt further diagnostics, including liver function testing. This article reviews the interpretation and limitations of serum liver enzyme activity and liver function tests. BACKGROUND The liver has a wide variety of metabolic functions ( Box 1 ). Because of these diverse metabolic roles, liver dysfunction is associated with a variety of sequelae and clinicopathologic abnormalities. The liver is unique in that it receives much of its blood supply (75%) from the portal venous system, which drains abdominal organs, such as the gastrointestinal (GI) tract, spleen, and pancreas. 1,2 This means that diseases of the pancreas and GI tract can secondarily affect the liver. The liver also metabolizes and/or excretes a variety of exogenous substances (ie, drugs and toxins) that may cause secondary liver injury. shutterstock.com/Jana Oudova CONTINUING EDUCATION LIVER DISEASE AND DYSFUNCTION can occur in cats and dogs of any age, sex, or breed. CE TEST To view the CE test for this article, please visit tvpjournal.com.