Describe the pathophysiology of diabetes mellitus in dogs and typical laboratory findings.

• A. Insulin deficiency or resistance → hyperglycemia, glucosuria, ketonuria; weight loss, polyuria, polydipsia; possible hyperlipidemia; confirm with persistent hyperglycemia and elevated fructosamine.
• B. Excess insulin causing hypoglycemia and weight gain.
• C. Hyperlipidemia with normal glucose and no signs.
• D. Diabetes resolves with time in dogs.

Answer: (A)

Diabetes mellitus in dogs results from insufficient insulin action, either due to loss of insulin-producing beta cells or reduced insulin effectiveness at tissues. When insulin is deficient or ineffective, glucose cannot enter muscle and fat cells efficiently and the liver continues to release glucose, causing persistent hyperglycemia.

Once blood glucose exceeds the kidney’s reabsorption capacity, glucose spills into the urine, drawing water with it and producing osmotic diuresis. That leads to polyuria and compensatory polydipsia. Because body cells aren’t getting usable energy, the body breaks down fat and protein for fuel, causing weight loss despite appetite. The increased fat breakdown also elevates fatty acids to the liver, which can produce ketone bodies; ketones in the urine or blood reflect this and can progress to diabetic ketoacidosis if the insulin deficiency is severe. Hyperlipidemia is also commonly seen due to enhanced lipolysis and hepatic lipid production.

Typical laboratory findings include persistent hyperglycemia and glucosuria, with ketonuria in cases of ketosis. Fructosamine is often elevated, reflecting average blood glucose over the past couple of weeks, helping confirm chronic hyperglycemia. Together, these signs and lab results align with the pattern of insulin deficiency or resistance driving the hyperglycemic state in dogs.