Antemortem diagnosis of urate nephrolithiasis in cetaceans is difficult. Since urate stones account for the majority of renal calculi, the discovery of radiolucent hyperechoic stones certainly raises one's index of suspicion; however it is by no means pathognomonic. We examine the ratio of urine uric acid to creatinine in fasted cetaceans to aid in diagnosis and treatment of urate stones.

In one confirmed and another suspected case of urate nephrolithiasis in two bottlenose dolphins, the uric acid to creatinine ratios were 0.42 and 0.14, which is 8 and 2 times greater than normal. Our normal ratios were determined from eight bottlenose dolphins whose urine was collected voluntarily before the first feeding in the morning and after receiving three, five, or greater than fifteen pounds of fish. The ratios between the groups were strikingly different. The fasting group was 0.07 (S.D. = 0.01), while the three, five and greater than 1 5 pound groups were 0. 20 (S. D. = 0. 1 3), 0.6 6 (S. D. = 0.26), and 1.39 (S.D. = 0.59) respectively. These data indicate that urine collected from fasting animals produced the most reliable ratios and are significantly lower than two clinical cases of urate nephrolithiasis.