Increased liver enzyme activities are sensitive indicators of primary hepatic disease, but they are also associated with extrahepatic diseases. The patient's signalment, clinical status, and pattern of liver enzyme activity can help in interpreting findings. The three basic liver enzyme patterns are (1) cholestatic, (2) hepatocellular leakage, and (3) mixed. Predominant increases in the activities of the cholestatic or inducible enzymes, alkaline phosphatase and I(3)-glutamyl transpeptidase, occur with endocrine disorders, cholestasis, neoplasia, benign nodular hepatic hyperplasia, and administration of certain drugs and occur idiopathically in certain breeds. Predominant increases in the activities of the hepatocellular leakage enzymes, alanine aminotransferase and aspartate aminotransferase, occur with circulatory disturbances, hepatotoxicities, infectious diseases, hepatitis, and neoplasia. A mixed pattern of increased liver enzyme activities may occur with hepatotoxicity or concurrent cholestasis and hepatocellular injury or necrosis.
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