Effects of storage time and temperature on pH, specific gravity, and crystal formation in urine samples from dogs and cats

Hasan Albasan Minnesota Urolith Center, Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Minnesota, St Paul, MN 55108.

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 DVM, MS
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Jody P. Lulich Minnesota Urolith Center, Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Minnesota, St Paul, MN 55108.

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 DVM, PhD, DACVIM
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Carl A. Osborne Minnesota Urolith Center, Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Minnesota, St Paul, MN 55108.

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 DVM, PhD, DACVIM
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Chalermpol Lekcharoensuk Department of Medicine, Faculty of Veterinary Medicine, Kasetsart University, Bangkok, Thailand 10900.

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 DVM, MPH, PhD
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Lisa K. Ulrich Minnesota Urolith Center, Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Minnesota, St Paul, MN 55108.

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Kathleen A. Carpenter Minnesota Urolith Center, Department of Small Animal Clinical Sciences, College of Veterinary Medicine, University of Minnesota, St Paul, MN 55108.

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Abstract

Objective—To determine effects of storage temperature and time on pH and specific gravity of and number and size of crystals in urine samples from dogs and cats.

Design—Randomized complete block design.

Animals—31 dogs and 8 cats.

Procedure—Aliquots of each urine sample were analyzed within 60 minutes of collection or after storage at room or refrigeration temperatures (20 vs 6°C [68 vs 43°F]) for 6 or 24 hours.

Results—Crystals formed in samples from 11 of 39 (28%) animals. Calcium oxalate (CaOx) crystals formed in vitro in samples from 1 cat and 8 dogs. Magnesium ammonium phosphate (MAP) crystals formed in vitro in samples from 2 dogs. Compared with aliquots stored at room temperature, refrigeration increased the number and size of crystals that formed in vitro; however, the increase in number and size of MAP crystals in stored urine samples was not significant. Increased storage time and decreased storage temperature were associated with a significant increase in number of CaOx crystals formed. Greater numbers of crystals formed in urine aliquots stored for 24 hours than in aliquots stored for 6 hours. Storage time and temperature did not have a significant effect on pH or specific gravity.

Conclusions and Clinical Relevance—Urine samples should be analyzed within 60 minutes of collection to minimize temperature- and time-dependent effects on in vitro crystal formation. Presence of crystals observed in stored samples should be validated by reevaluation of fresh urine. (J Am Vet Med Assoc 2003;222:176–179)

Abstract

Objective—To determine effects of storage temperature and time on pH and specific gravity of and number and size of crystals in urine samples from dogs and cats.

Design—Randomized complete block design.

Animals—31 dogs and 8 cats.

Procedure—Aliquots of each urine sample were analyzed within 60 minutes of collection or after storage at room or refrigeration temperatures (20 vs 6°C [68 vs 43°F]) for 6 or 24 hours.

Results—Crystals formed in samples from 11 of 39 (28%) animals. Calcium oxalate (CaOx) crystals formed in vitro in samples from 1 cat and 8 dogs. Magnesium ammonium phosphate (MAP) crystals formed in vitro in samples from 2 dogs. Compared with aliquots stored at room temperature, refrigeration increased the number and size of crystals that formed in vitro; however, the increase in number and size of MAP crystals in stored urine samples was not significant. Increased storage time and decreased storage temperature were associated with a significant increase in number of CaOx crystals formed. Greater numbers of crystals formed in urine aliquots stored for 24 hours than in aliquots stored for 6 hours. Storage time and temperature did not have a significant effect on pH or specific gravity.

Conclusions and Clinical Relevance—Urine samples should be analyzed within 60 minutes of collection to minimize temperature- and time-dependent effects on in vitro crystal formation. Presence of crystals observed in stored samples should be validated by reevaluation of fresh urine. (J Am Vet Med Assoc 2003;222:176–179)

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