Definition

Fasting hyperglycemia

Glucosuria suggests diabetes but is not definitive for the diagnosis because, for example, renal tubular functional defects (Fanconi syndrome in Basenji and other breeds) can cause glucosuria

Classification

Type I and Type II are the main two types of diabetes mellitus

Type I diabetes

Type I diabetes is characterized by lack of insulin production by the pancreatic beta cells of the islets of Langerhans; it is also known as IDDM or Insulin Dependent Diabetes Mellitus because insulin injections are required for treatment

Type I is the type most commonly diagnosed in dogs because it causes profound obligatory solute (glucose) osmotic diuresis resulting in urinary accidents which prompts dog owners to seek veterinary care

The catabolic state that follows is severe and weight loss is often profound for two reasons:

glycogenolysis (recall that stored glycogen in terrestrial mammals' liver is limited) is followed within a few hours of insulin lack by gluconeogenesis

gluconeogenesis is much less limited and occurs by way of skeletal muscle protein catabolism and amino acids (principally alanine) from this source are the basis of hepatic over production of new glucose that cannot be used by peripheral cells due to the lack of insulin

under use and over production of glucose contribute to solute diuresis as the renal tubular threshold for glucose re-absorption continues to be exceeded and protein catabolism also continues

in the quest for a utilizable fuel (energy source), in another day or two a second major catabolic process is up regulated: ketone production

the ketone bodies (acetoacetic acid, β-hydroxybutyric acid and acetone) are made by the liver from the mobilization and catabolism of fat stores;

within 7 to 10 days after marked reduction in insulin production, severe weight loss is obvious in the dog with Type I diabetes because of the catabolism of both muscle and fat

Type II diabetes

Type II diabetes is characterized more by peripheral resistance to the effects of insulin at the receptor sites than to an absolute lack of insulin; it is also known as Non-Insulin Dependent Diabetes Mellitus or NIDDM because insulin injections are not always required for treatment

More cats have Type II diabetes than is recognized in dogs and the severity of weight loss and degree of solute diuresis is often less obvious than it is in dogs

Depending on the cat population studied, it is believed that from 50% to 80% of diabetic cats have Type II diabetes at the time of diagnosis

diabetic cats, like dogs, have glucose diuresis due to hyperglycemia resulting in glomerular filtrate glucose concentration that exceeds renal tubular re-absorptive capabilities but the magnitude of these pathophysiologic events are often not as great as in dogs