Diabetes mellitus is a metabolic disorder characterized by a congenital (similar to juvenile-onset or Type I diabetes mellitus in people) or acquired (similar to adult-onset or Type II diabetes mellitus in people) inability to transport sugar from the bloodstream into cells. Once inside cells, sugar (glucose) is used to generate the energy that is essential for normal cellular function. Diabetes in animals is most commonly the acquired form and typically occurs in middle-aged to older pets. The disease results when glucose transport channels on cell membranes are insensitive to the effects of insulin (or when there are too few channels) or when the quantity of insulin produced by the pancreas is inadequate to activate the number of glucose channels needed to maintain normal cellular metabolism. In other words, insulin is the “key” that allows special “gates” for sugar transport across cell membranes to be opened. A diabetic, therefore, has too much glucose in the bloodstream where most of it cannot be utilized, and not enough glucose within the cells themselves, where it is most needed for energy. As a result, cells attempt to derive energy from alternate metabolic pathways, such as fat breakdown. Excessive use of these alternate energy pathways culminates in production of harmful by-products called ketones. The accumulation of ketones causes the body’s pH to become acidic (ketoacidosis) which makes the cellular environment inhospitable for normal metabolic functions. This condition can ultimately become life-threatening and requires aggressive medical therapy.
Fortunately, most diabetics give some indication of their underlying condition, such as drinking and urinating excessively, before they develop ketoacidosis. Treating diabetics before they become ketotic is considerably more straightforward, safer, and of course less expensive than taking a "wait-and-see" approach to changes in drinking behavior. Equally important, diagnostic testing may reveal other serious conditions which can cause excessive urination and drinking, such as kidney or liver disease, adrenal hormone or electrolyte imbalances and uterus infections.