Animals with high blood glucose levels urinate frequently and in large amounts to rid their bodies of excess glucose.
Excessive urination often is accompanied by excessive thirst (medical term polydipsia [pah-lee-DIP-see-uh]; abreviated as PD). Diabetic animals often drink incessantly because they are dehydrated from the cell-dehydrating effects of hyperglycemia, plus the effects of their bodies casting off the excess glucose through urination, taking hydration with it.
The extra urine is full of glucose, as can be easily seen using Urine testing stix, and is therefore hospitable to bacteria. This can easily lead to a urinary tract infection. Also see Laboratory tests for more information.
The concentration (or lack of it) is determined by what's called a urine specific gravity test. The basis for comparison used is the specific gravity of water, which is 1.000. The specific gravity of urine which has a large amount of glucose (such as the urine of a yet to be controlled diabetic) increases by 0.010 units due to the amount of glucose present in it. 
- ↑ 1.0 1.1 Lunn, Katharine F., James Katherine M. (2007). Normal and Abnormal Water Balance: Polyuria and Polydipsia. Compendium.
- ↑ Bartges, Joe (2011). Urine Heaven: Of Bugs and Drugs-Urinary Tract Infections. Western Veterinary Conference.
- ↑ Daniels, Joshua B., Chew, Dennis J. (2011). Diagnosis and Treatment of Routine and Difficult Urinary Infections in Dogs. Western Veterinary Conference.
- ↑ Specific Gravity of Urine. Cornell University.
- ↑ 5.0 5.1 Polydipsia & Polyuria. Petplace.com.
- ↑ Pounds to Kilograms/Kilograms to Pounds online converter. Open Toronto.