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32 LIVER ENZYME INTERPRETATION PEER REVIEWED CASE 1 Signalment and Presentation A 3-month-old female intact Irish wolfhound presents for stunted growth and episodes of intermittent lethargy and disorientation. Results of Diagnostic Testing A serum biochemistry panel is performed, with the results in Table A. The fasted ammonia concentration is 175 mcg/dL (normal range, 0–50 mcg/dL). Preprandial and postprandial (2-hour) SBA are 40 mcmol/L (normal, 0–8 mcmol/L) and 102 mcmol/L (normal, 0–30 mcmol/L), respectively. Interpretation The combination of hypoalbuminemia, decreased BUN, and hypocholesterolemia suggests decreased hepatic synthetic capacity. The ALT and AST activities are within normal limits, making hepatocellular damage unlikely; the ALP activity is only mildly elevated, probably because the dog is growing. The ammonia concentration and SBA results suggest portosystemic shunting and/or hepatic insufficiency. Given the patient's signalment, clinical findings, and laboratory abnormalities, a congenital portosystemic shunt is likely and imaging (ultrasonography and/or computed tomography) is warranted. CASE 2 Signalment and Presentation An 8-year-old male neutered Labrador retriever presents for a 3-month history of decreased appetite and weight loss. Results of Diagnostic Testing A serum biochemistry panel is performed, with the results in Table B. The fasted ammonia concentration is <15 mcg/dL (normal range, 0–50 mcg/dL). Preprandial and postprandial (2-hour) bile acids are 2.9 mcmol/L (normal, 0–8 mcmol/L) and 14.5 mcmol/L (normal, 0–30 mcmol/L), respectively. Interpretation The ALT activity is 2.4 times the upper limit of the reference interval, while the ALP activity is only 1.3 times the upper limit of the reference interval. This, along with the increased serum AST activity, is consistent with a hepatocellular damage pattern. The ammonia concentration and SBA results rule out portosystemic shunting and do not support the presence of severe liver dysfunction. However, hepatobiliary disease is not excluded and further testing is indicated. Abdominal ultrasonography would be a logical next step. If the ALT is persistently increased and no evidence supports the presence of extrahepatic disease, liver biopsy would be indicated. TABLE A Case 1 Serum Biochemistry Results ANALYTE VALUE NORMAL RANGE BUN 3 mg/dL 7–27 mg/dL Total protein 5.0 g/dL 5.2–8.2 g/dL Albumin 2.0 g/dL 2.4–4 g/dL Cholesterol 79 mg/dL 110–220 mg/dL Glucose 118 mg/dL 74–140 mg/dL ALT 50 U/L 10–130 U/L AST 15 U/L 10–34 U/L ALP 180 U/L 24–147 U/L GGT <10 U/L 0–25 U/L Total bilirubin 0.1 mg/dL 0–0.8 mg/dL TABLE B Case 2 Serum Biochemistry Results ANALYTE VALUE NORMAL RANGE BUN 13 mg/dL 7–27 mg/dL Total protein 6.2 g/dL 5.2–8.2 g/dL Albumin 3.3 g/dL 2.4–4 g/dL Cholesterol 179 mg/dL 110–220 mg/dL Glucose 110 mg/dL 74–140 mg/dL ALT 550 U/L 10–130 U/L AST 50 U/L 10–34 U/L ALP 198 U/L 24–147 U/L GGT <10 U/L 0–25 U/L Total bilirubin 0.2 mg/dL 0–0.8 mg/dL Case Studies