Today's Veterinary Practice

MAY-JUN 2017

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38 LIVER ENZYME INTERPRETATION PEER REVIEWED the absence of portosystemic shunts it is not as sensitive for detecting hepatic insufficiency. 17 Protein C Protein C is an anticoagulant protein produced by the liver. Measurement of protein C provides information regarding liver function and perfusion. In one study, 18 dogs with congenital and acquired portosystemic shunts, hepatic failure, and chronic hepatitis had decreased levels of protein C, which distinguished them from dogs with microvascular dysplasia (portal vein hypoplasia) and those without hepatobiliary disease. With use of a cutoff value of 70% activity, protein C could distinguish dogs with congenital portosystemic shunt from those with microvascular dysplasia with a sensitivity of 93% and a specificity of 88%. CONCLUSIONS Increased liver enzyme activities are common results in small animal practice and can suggest patterns of liver disease, including hepatocellular damage, cholestasis, or both. Liver enzymes, especially ALP, are not specific for primary liver disease. To evaluate their clinical significance, a combination of history, clinical signs, physical examination, diagnostic imaging, and other liver function test results must be considered. Changes such as hypocholesterolemia or hypoalbuminemia can suggest hepatic dysfunction. Measuring SBA or ammonia concentrations provides a more accurate assessment of liver function, but it is important to be aware that patients with normal liver function test results can still have liver disease. Although these laboratory tests play an important role in diagnosing canine and feline liver disease, definitive diagnosis usually requires a combination of diagnostic imaging and cytologic or histologic assessment of liver tissue. REFERENCES 1. Hall JE, Guyton AC. Guyton and Hall Textbook of Medical Physiology, 12th ed. Philadelphia: Saunders/Elsevier; 2011. 2. Allison RW. Laboratory evaluation of the liver. In: Thrall M, Weiser, G, Allison RW, Campbell TW (eds): Veterinary Hematology and Clinical Chemistry, 2nd ed. Oxford: John Wiley & Sons; 2012:401-424. 3. Lidbury JA, Steiner JM. Diagnostic evaluation of the liver. In: Washabau RJ, Day MJ, eds: Canine & Feline Gastroenterology. St. Louis, MO: Elsevier Saunders; 2013:863-875. 4. Valentine BA, Blue JT, Shelley SM, et al. Increased serum alanine aminotransferase activity associated with muscle necrosis in the dog. J Vet Intern Med 1990; 4(3):140-143. 5. Webster CRL, Cooper JC. Diagnostic approach to hepatobiliary disease. In: Bonagura J, Twedt D, eds. Kirk's Current Veterinary Therapy, 15th ed. St. Louis, MO: Elsevier; 2014:569-575. 6. Comazzi S, Pieralisi C, Bertazzolo W. Haematological and biochemical abnormalities in canine blood: frequency and associations in 1022 samples. J Small Anim Pract 2004; 45(7):343-349. 7. Center SA, Slater MR, Manwarren T, et al. Diagnostic efficacy of serum alkaline phosphatase and gamma-glutamyltransferase in dogs with histologically confirmed hepatobiliary disease: 270 cases (1980- 1990). JAVMA 1992; 201(8):1258-1264. 8. Center SA, Baldwin BH, Dillingham S, et al. Diagnostic value of serum gamma-glutamyl transferase and alkaline phosphatase activities in hepatobiliary disease in the cat. JAVMA 1986; 188(5):507-510. 9. Kaneko JJ, Harvey J, Bruss ML. Diagnostic enzymology of domestic animals. In: Clinical Biochemistry of Domestic Animals, 6th ed. St. Louis, MO: Elsevier; 2008:358-361. 10. Rabin B, Nicolosi RJ, Hayes KC. Dietary influence on bile acid conjugation in the cat. J Nutr 1976; 106(6):1241-1246. 11. Ruland K, Fischer A, Hartmann K. Sensitivity and specificity of fasting ammonia and serum bile acids in the diagnosis of portosystemic shunts in dogs and cats. Vet Clin Pathol 2010; 39(1):57-64. 12. Center SA, ManWarren T, Slater MR, et al. Evaluation of twelve- hour preprandial and two-hour postprandial serum bile acids concentrations for diagnosis of hepatobiliary disease in dogs. JAVMA 1991; 199(2):217-226. 13. Lidbury JA, Cook AK, Steiner JM. Hepatic encephalopathy in dogs and cats. J Vet Emerg Crit Care (San Antonio) 2016; 26(4):471- 487. 14. Gerritzen-Bruning MJ, van den Ingh TS, Rothuizen J. Diagnostic value of fasting plasma ammonia and bile acid concentrations in the identification of portosystemic shunting in dogs. J Vet Intern Med 2006; 20(1):13-19. 15. Meyer DJ, Strombeck DR, Stone EA, et al. Ammonia tolerance test in clinically normal dogs and in dogs with portosystemic shunts. JAVMA 1978; 173(4):377-379. 16. Rothuizen J, van den Ingh TS. Rectal ammonia tolerance test in the evaluation of portal circulation in dogs with liver disease. Res Vet Sci 1982; 33(1):22-25. 17. Walker MC, Hill RC, Guilford WG, et al. Postprandial venous ammonia concentrations in the diagnosis of hepatobiliary disease in dogs. J Vet Intern Med 2001; 15(5):463-466. 18. Toulza O, Center SA, Brooks MB, et al. Evaluation of plasma protein C activity for detection of hepatobiliary disease and portosystemic shunting in dogs. JAVMA 2006; 229(11):1761-1771. Brigitte B. McAtee Brigitte B. McAtee received her DVM from Auburn University. She is currently a second-year internal medicine resident at Texas A&M; University in College Station, Texas. Her clinical and research interests include infectious and immune-mediated diseases. Jonathan A. Lidbury Jonathan A. Lidbury graduated from the University of Glasgow and completed his internal medicine residency at Texas A&M; University. Jonathan is an assistant professor of small animal internal medicine and the associate director for clinical services of the Gastrointestinal Laboratory at Texas A&M; University. His clinical interests are small animal hepatology and gastroenterology, and he is involved in a wide range of research in these fields.

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