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Effect on urine specific gravity by the addition of glucose

Behrend EN, Botsford AN, et al.  Effect on urine specific gravity of the addition of glucose to urine samples in dogs and cats.  Am J Vet Res 2019;80:907-911.

Interpreting urine specific gravity in feline patients with glycosuria can pose a diagnostic dilemma, as dilute urine can be found in cats with diabetes mellitus, hyperthyroidism and other endocrine diseases, chronic kidney disease, pyelonephritis, and hypokalemia, as well as other conditions, any of which can coexist with diabetes mellitus.  If the urine is dilute due to osmotic diuresis attributable to glycosuria, is it then still possible to assess renal urine concentrating ability in such a sample?

This laboratory study evaluated the results of addition of glucose to species-specific pooled urine samples with various urine specific gravities (USGs) from 35 cats and 45 dogs, to determine the effects of varying amounts of glucose on USG.  Glucose was added to each of the pooled feline urine samples to reach a final concentration of 2,400 mg/mL, and then serial dilutions were perfomed on the sample.

Addition of any solute to urine, including glucose, will affect the density of the urine, so addition of the glucose to the pooled feline urine samples increased the USGs.  In the feline urine pooled samples, glucose was added to produce concentrations of 600, 1,200, and 2,400 mg/dL.  In the urine samples that were most concentrated (highest USGs) prior to the addition of glucose, there was little change in the USG.  Addition of glucose to the urine samples did not cause clinically important changes in the USG.  The USG of a glycosuric urine specimen from a cat or dog still therefore reflects renal urine concentrating ability in that animal. [PJS]

See also:

Rishniw M, Bicalho R. Factors affecting urine specific gravity in apparently healthy cats presenting to first opinion practice for routine evaluation. J Feline Med Surg 2015;17:329-37.