EFFECTS OF VARIOUS METHODS OF PRESERVATION ON THE STABILITY OF URIC-ACID IN FROZEN CANINE URINE

Objective-To evaluate the effects of dilution and alkalinization, sepa rately and together, on the stability of uric acid in canine urine sto red at -20 C. Design-Prospective-controlled study. Animals-5 dogs with confirmed ammonium urate uroliths, 6 Beagles, and 6 mixed-breed dogs. Procedure-Dogs were fed a 31.4% protein (dry weight), meal-based diet for 21 days, and urine samples were collected on day 22. Urine sample s were preserved, using combinations of dilution and alkalinization, a nd divided into 1-ml aliquots for storage at -20 C for 1 to 12 weeks, Urine uric acid concentrations were measured, using high-performance l iquid chromatography, on day of collection (baseline), and after 1, 2, 4, 8, and 12 weeks. Results-Alkalinization did not have a significant effect on reproducibility of measurements of uric acid concentrations in urine; however, dilution did have a significant effect. Compared w ith baseline, uric acid concentrations in urine samples collected from dogs with ammonium urate uroliths and Beagles and diluted 1:10 or 1:2 0 with deionized water were not different after storage for 1 to 12 we eks. Uric acid concentrations in urine samples collected from mixed-br eed dogs did not differ from baseline values during the 12-week storag e period whether samples were undiluted or were diluted 1:10 or 1:20 w ith deionized water. Conclusions-Measurements of uric acid concentrati on are most reproducible in canine urine samples stored at -20 C for 1 to 12 weeks when samples are diluted 1:20 with deionized water. Clini cal Relevance-To ensure reproducibility of measurements of uric acid c oncentration in urine samples collected from dogs affected with urate uroliths, urine should be diluted 1:20 with deionized water. Alkaliniz ation is not necessary, and is not recommended because of the addition al step in processing and its potential to interfere with measurement of other urinary analytes.