Laboratory methods for evaluating canine portosystemic shunts

In dogs with reduced liver function (portosystemic shunting, parenchymal liver disease), metabolic functions of the liver are disrupted, resulting in increased concentrations of ammonia, amino acids and poorly water soluble uric acid in the blood. This is associated with hepatoencephalopathy and excretion of ammonium-urate crystals in the urine. The analytes are measured in the blood and serum and urate crystals are easily recognised in the urine sediment under light microscopy. Changes in liver function can be documented by measurement of pre and post prandial serum bile acid concentrations and, when available, whole blood ammonia concentration. Measurement of serum amino acid concentrations are routinely performed for people but infrequently applied in animals although testing can be available through human laboratories. Energy dispersive analysis is a new, semi-quantitative method for examining urinary crystals and is available to veterinarians. This report describes the whole blood ammonia, serum aromatic amino acid concentrations and urinary crystal analysis in a dog diagnosed with a portosystemic shunt. The urine crystals were identified as sodium and potassium urate using energy dispersive analysis. Purchasing a portable ammonia-meter for whole blood ammonia measurement and sending serum samples to human or research laboratories for determination of amino acid concentrations could provide useful additional information for clinicians assessing dogs with hepatic dysfunction. Because many urinary crystals are morphologically similar, crystal analysis can be useful to determine their content and hence their pathogenesis. This information is especially useful when the typical ammonium biurate crystals are absent