Editorial Type:
Urology

Association between urine osmolality and specific gravity in dogs and the effect of commonly measured urine solutes on that association

Jennifer A. Ayoub Department of Veterinary Clinical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803.

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Hugues Beaufrere Department of Zoological Medicine, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803.

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Mark J. Acierno Department of Veterinary Clinical Sciences, School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803.

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DOI:
https://doi.org/10.2460/ajvr.74.12.1542
Volume/Issue:
Volume 74: Issue 12
Online Publication Date:
01 Dec 2013
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Abstract

Objective—To determine the association between urine osmolality and specific gravity (USG) in dogs and to evaluate the effect of commonly measured urine solutes on that association.

Animals—60 dogs evaluated by an internal medicine service.

Procedures—From each dog, urine was obtained by cystocentesis and USG was determined with a refractometer. The sample was divided, and one aliquot was sent to a diagnostic laboratory for urinalysis and the other was frozen at −80°C until osmolality was determined. Urine samples were thawed and osmolality was measured in duplicate with a freezing-point depression osmometer. The correlation between mean urine osmolality and USG was determined; the effect of pH, proteinuria, glucosuria, ketonuria, bilirubinuria, and hemoglobinuria on this relationship was investigated with multiple regression analysis.

Results—The Pearson correlation coefficient between urine osmolality and USG was 0.87. The final multivariable regression model for urine osmolality included USG and the presence of ketones; ketonuria had a small negative association with urine osmolality.

Conclusions and Clinical Relevance—Results indicated a strong linear correlation between osmolality and USG in urine samples obtained from dogs with various pathological conditions, and ketonuria had a small negative effect on that correlation.

Abstract

Objective—To determine the association between urine osmolality and specific gravity (USG) in dogs and to evaluate the effect of commonly measured urine solutes on that association.

Animals—60 dogs evaluated by an internal medicine service.

Procedures—From each dog, urine was obtained by cystocentesis and USG was determined with a refractometer. The sample was divided, and one aliquot was sent to a diagnostic laboratory for urinalysis and the other was frozen at −80°C until osmolality was determined. Urine samples were thawed and osmolality was measured in duplicate with a freezing-point depression osmometer. The correlation between mean urine osmolality and USG was determined; the effect of pH, proteinuria, glucosuria, ketonuria, bilirubinuria, and hemoglobinuria on this relationship was investigated with multiple regression analysis.

Results—The Pearson correlation coefficient between urine osmolality and USG was 0.87. The final multivariable regression model for urine osmolality included USG and the presence of ketones; ketonuria had a small negative association with urine osmolality.

Conclusions and Clinical Relevance—Results indicated a strong linear correlation between osmolality and USG in urine samples obtained from dogs with various pathological conditions, and ketonuria had a small negative effect on that correlation.

Contributor Notes

Address correspondence to Dr. Ayoub (jenaayoub@yahoo.com).

Dr. Ayoub's present address is Palm Beach Veterinary Specialists, 3884 Forest Hill Blvd, West Palm Beach, FL 33406. Dr. Beaufrere's present address is Health Sciences Center, Ontario Veterinary College, University of Guelph, Guelph, ON N1G 2W1, Canada.

The study was performed in its entirety at the School of Veterinary Medicine, Louisiana State University, Baton Rouge, LA 70803.

The authors thank Dr. Stephen D. Gaunt for technical assistance.

Cover American Journal of Veterinary Research
American Journal of Veterinary Research
Publication Date:
01 Dec 2013

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