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Comparison of the Techniques of Evaluation of Urine Dilution/Concentration in the Dog

Authors

  • O. Dossin,

    1. Addresses of authors: Département de Médecine Interne des Animaux de Compagnie et de Sport and
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  • C. Germain,

    1. Département des Sciences Biologiques & UMR 181 Physiopathologie et Toxicologie Expérimentales, Ecole Nationale Vétérinaire, 23 Chemin des Capelles, 31076 Toulouse Cedex, France;
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  • J. P. Braun

    1. Département des Sciences Biologiques & UMR 181 Physiopathologie et Toxicologie Expérimentales, Ecole Nationale Vétérinaire, 23 Chemin des Capelles, 31076 Toulouse Cedex, France;
    2. Corresponding author: Tel.: +33 561 19 38 44; Fax: +33 561 19 39 78; E-mail: jp.braun@envt.fr
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Département des Sciences Biologiques & UMR 181 Physiopathologie et Toxicologie Expérimentales, Ecole Nationale Vétérinaire, Toulouse Cedex, France

Summary

The objective of this study was to evaluate the quality of the measurement of dog urine dilution/concentration by comparing osmolality with three methods of specific gravity (USG) measurement, i.e. weighing, refractometry and test strips. In unselected urine samples from 182 dogs there was a better agreement between osmolality and USG determination by refractometry (r = 0.92) than by weighing (r = 0.82) or by test strips (r = 0.27). There was an almost linear relationship between osmolality and USG:

osmolality (mOsm/kg) = 36646(34318/38974) × (USGref − 1) + 25(−39/88); calculated osmolality differed from measured osmolality by more than 500 mOsm/kg in only 8 of 181 samples. There was a good agreement between USG determination by weighing and refractometry: USGref = 1.000(0.905/1.095) ×USGweighing − 0.0004(−0.0019/0.0027), with a moderate bias. Only 12% of the differences between the two methods exceeded 0.010. Test strip assessment of USG was unreliable because of systematic underestimation and should not be used for dog urine. Refractometry is the best technique for routine evaluation of urine concentration/dilution when osmometry is not available.

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