Today's Veterinary Practice

MAY-JUN 2017

Today's Veterinary Practice provides comprehensive information to keep every small animal practitioner up to date on companion animal medicine and surgery as well as practice building and management.

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hepatic functional mass cannot extract the additional ammonia, leading to an excessive increase in plasma ammonia concentration. The main indication for this test is concern for hepatic insufficiency that is not supported by routine laboratory testing. This test is unnecessary for dogs with increased baseline ammonia, in addition to posing a risk for hepatic encephalopathy in these patients. Disadvantages of oral ammonia administration include 15 : • Absorption depends on gastric emptying. • Vomiting can occur. • It is stressful to the patient. • The taste of the ammonium chloride is unpleasant. The rectal ammonia tolerance test avoids these problems ( Box 5 ). 16 However, we do not routinely perform either test in dogs or cats. Postprandial Venous Ammonia Tolerance Test The postprandial ammonia tolerance test involves a procedure similar to that of the oral or rectal ammonia tolerance test except that digested food provides the ammonia challenge and the disadvantages of oral administration are avoided. The patient is fed a commercial diet containing about 30% protein to provide 33 kcal/kg, and a blood sample is collected 6 hours after feeding. This test was reported to have 91% sensitivity for the detection of portosystemic shunting, but in BOX 5 Rectal Ammonia Tolerance Test 16 Procedure 1. Fast animal for 12 hours and collect a blood in a heparin anticoagulant tube (immediately place in an ice bath, separate plasma as soon as possible, and run assay within 30 minutes of collection). 2. Give ammonium chloride rectally (5% solution; 2 mL/kg) through a catheter inserted 20 to 35 cm into the colon. 3. Collect blood samples 20 and 40 minutes after ammonium chloride administration. Interpretation of Results • The preadministration to postadministration increase of blood ammonia concentration in normal dogs should be about 2- to 2.5-fold. • Dogs with severe ammonia concentration increases of 3- to 10-fold likely have hepatobiliary disease and/or portosystemic shunting. 36 LIVER ENZYME INTERPRETATION PEER REVIEWED

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