Uric acid Uric acid is formed from the catabolism of the nucleic acids, adenine and guanine. Both of these nucleic acids are converted to xanthine, guanine directly and adenine after being converted to hypoxanthine first. Xanthine is converted to uric acid via the action of xanthine oxidase. Uric acid is usually converted by hepatic uricase to allantion, which is excreted in the urine of most dog breeds, except the dalmation. The dalmation has a defect in uric acid uptake into hepatocytes, resulting in decreased conversion to allantion. Therefore, this breed excretes uric acid, and not allantion, in the urine. The supersaturation of uric acid in the urine of dalmations predisposes this breed to urate urolithiasis. Main uses for urate measurement Urinary uric acid This is used to detect excessive urate excretion in breeds, such as dalmations, and to monitor response to therapy with allopurinol. The best method for measuring urinary urate excretion is from a 24-hour urine collection. Uric acid precipitates rapidly when urine is cooled, so the sample must be resuspended and a well-mixed aliquot provided to the laboratory, to prevent falsely decreased values due to precipitation. The determination of uric acid/creatinine ratios does not appear to be a reliable test for quantifying urinary uric acid excretion, as the values are influenced by diet. Avian species Uric acid is the major end product of nitrogen metabolism in avian species. It constitutes approximately 60 to 80% of the total nitrogen excreted in avian urine and is secreted actively by the renal tubules. Measurement of plasma or serum uric acid is used as an index of renal function in birds. Increases in uric acid concentration are seen in the following situations: 1) Artifact: Uric acid can also be increased artifactually in samples from toe-nail clippings because of fecal urate contamination. 2) Post-prandial: Uric acid concentrations will increase after a meal in carnivorous birds. 3) Renal disease: Concentrations increase when the kidney has lost >70% of its functional capacity. Cell death Uric acid is found in high concentration within cells. In acut tumor lysis syndrome, high concentrations of uric acid are observed.

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