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Abstract
Urinalysis is a valuable tool for assessing the renal health of marine mammals. While retrospective and population renal health studies often use frozen urine samples, it has not been determined if the freeze-thaw process alters urine values from bottlenose dolphins (Tursiops truncatus). The primary objective of our study was to compare the values of 38 fresh and frozen paired urine samples collected from 20 bottlenose dolphins at the U.S. Navy Marine Mammal Program. Paired t-tests and chi-squared tests were conducted to assess the effects of storage at -80° C for 2 to 301 d, and a subsequent thaw on urine specific gravity; pH; creatinine; protein:creatinine ratio; quantitative protein; uric acid; uric acid:reatinine ratio; and categorical characterizations of color, clarity, glucose, ketones, occult blood, protein levels, and crystals. The freeze-thaw cycle decreased urinary pH and increased urinary uric acid (p = 0.04 and 0.02, respectively). There were no other significant changes in urine variable values, including urinary uric acid concentration by grams of creatinine, when comparing fresh and frozen-thawed urine samples. Urinary uric acid concentration by grams of creatinine is the most accurate uric acid measurement when frozen-thawed samples are used. Urinary pH should be measured in fresh samples to avoid falsely decreased pH.
Key Words: cetacean, urine storage effects, bottlenose dolphin, Tursiops truncatus, urinalysis, temperature
Introduction
Bottlenose dolphins (Tursiops truncatus) are sus- ceptible to urate nephrolithiasis, and urinalyses are being used to identify risk factors for nephro- lith formation (Venn-Watson et ah, 2010a, 2010b). Retrospective and population studies may require that urinalyses be performed on frozen samples that have been stored for various periods of time. Previous studies of terrestrial mammalian urine have demonstrated that storage time and tem- perature may or may not affect urinary proteins, pH, and uric acid; and rarely affect urine creati- nine and specific gravity (Miki & Sudo, 1998; Klasen et ah, 1999; Schultz et ah, 2001; Albasan et ah, 2003). Further, crystal formation that occurs during storage of urine from terrestrial mammals with uroliths can change uric acid values (Bartges et ah, 1996; Wells et ah, 2004). In our study, we used urine samples collected from bottlenose dol- phins at the U.S. Navy Marine Mammal Program (MMP) to test the null hypothesis that there would be no...