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, separately and together, on the stability of uric acid in canine urine stored 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), meat-based diet for 21 days, and urine samples were collected on day 22. Urine samples were preserved, using combinations of dilution and alkalinization, and divided into 1-ml aliquots for storage at -20 C for 1 to 12 weeks. Urine uric acid concentrations were measured, using high-performance liquid 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 with baseline, uric acid concentrations in urine samples collected from dogs with ammonium urate uroliths and Beagles and diluted 1:10 or 1:20 with deionized water were not different after storage for 1 to 12 weeks. Uric acid concentrations in urine samples collected from mixed-breed dogs did not differ from baseline values during the 12-week storage period whether samples were undiluted or were diluted 1:10 or 1:20 with deionized water.

CONCLUSIONS

Measurements of uric acid concentration 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.

CLINICAL RELEVANCE

To ensure reproducibility of measurements of uric acid concentration in urine samples collected from dogs affected with urate uroliths, urine should be diluted 1:20 with deionized water. Alkalinization is not necessary, and is not recommended because of the additional step in processing and its potential to interfere with measurement of other urinary analytes.