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Diabetes Mellitus

Diabetes Mellitus-Feline

Increased thirst, increased urination, and weight loss despite an increased appetite are all signs of Diabetes Mellitus and can be diagnosed when glucose is found in the urine and the blood sugar is excessively high.

by Rhonda Schulman, DVM,
Diplomate American College of Veterinary Internal Medicine


Diabetes mellitus is one of the most common endocrine diseases seen in dogs and cats.  Similar to the disease in humans, diabetes mellitus is a condition in which the body does not have enough insulin. The lack of insulin can be absolute (type I) or can be relative wherein the body is unable to respond appropriately to insulin (type II).  Insulin acts as a gatekeeper in the body – when it is present and the receptors for it respond normally, glucose can pass into the cells where it is metabolized to provide energy for that cell’s functions. In a diabetic, the blood glucose (sugar) becomes elevated because without insulin, the glucose cannot pass into the cells; hence, the tissues are being starved. The goal of treatment is to correct this metabolic abnormality so that the cells have the glucose they need to carry on their normal functions in the body.

Clinical Signs

The most common clinical signs of diabetes are increased thirst, increased urination, and weight loss despite an increased appetite. The increased thirst and urination occur because the high levels of sugar in the blood lead to the presence of sugar in the urine.  The sugar in the urine pulls more water into the urine, leading to the formation of larger volumes of urine. Excessive thirst occurs, as the patient must drink more to make up for the increased urination. As mentioned before, the body’s tissues are being starved which leads to weight loss and increased hunger. These signs improve when the blood glucose is being controlled appropriately and worsen when the control is poor.

Some uncontrolled diabetics will develop a condition known as ketoacidosis. Ketones are a byproduct of abnormal fat metabolism. Some tissues in the body can use ketones as an alternative energy source in states of starvation. Ketones are acids and because they are being formed in amounts that exceed the body’s normal production the amount of acid in the blood overwhelms the body’s ability to maintain “acid/base balance” – a condition known as acidosis (too much acid in the blood). Ketoacidosis usually occurs only in the face of another condition, most frequently, an infection; however pancreatitis and other endocrine diseases can precipitate a ketoacidotic episode as well. The most common signs associated with ketoacidosis are lack of appetite, vomiting and lethargy.

It is not uncommon for diabetic dogs to develop cataracts. Excess sugar in the lens of the eye draws in excess water, which disrupts the fibers of the eye. The dogs’ eyes may appear cloudy and the dog will lose sight. Even reasonably well-controlled diabetic dogs may develop cataracts. Veterinary ophthalmologists can surgically correct cataracts.

Poorly controlled diabetes mellitus in cats may lead to diabetic neuropathy. Cats with diabetic neuropathy will have a plantigrade stance and walk “down on their hocks.” Diabetic neuropathy may or may not improve with better control of the diabetes.


Diabetes mellitus is diagnosed when 1) glucose is found in the urine and 2) the blood sugar is excessively high. When cats are stressed, they release other hormones, which can cause a temporary elevation in their blood sugar. A fructosamine may be recommended in cats to help determine whether the cat is truly diabetic or not. A fructosamine measures the level of glycosylated proteins (proteins which have had a sugar attached to them) and gives an idea of the blood sugar concentrations over the past few weeks. It is common when establishing a diagnosis of diabetes mellitus in a dog or cat to run baseline blood work and to culture the urine to rule out any concurrent problems. Based upon the history and clinical findings, other testing may also be suggested.


Most dogs are Type I diabetics and therefore require insulin as the major form of therapy. Dogs typically require insulin for the remainder of their lives. Cats may be type I or type II diabetics but usually benefit from insulin therapy initially regardless. Many cats, like dogs, are Type I diabetics and therefore require insulin life-long. Cats with Type II diabetes suspected to be secondary to other conditions (including pancreatitis, chronic infections and cancer) may or may not require insulin long-term.  In such cats, close monitoring of their blood or urine glucose helps us to determine whether they still require insulin as their other condition(s) resolve.

Diet is important in the management of feline diabetes mellitus. Cats are obligate carnivores.  This means they regulate their sugar best when they eat a high protein diet.  Numerous prescription diets are available for diabetic cats (e.g. Purina DM, Science Diet M/D, etc.). Another option is an over-the-counter kitten food. Dogs appear to respond best to high fiber diets such as Science Diet W/D, Purina DCO, Royal Canine Diabetic Formula to name a few. Over the counter diets meant for weight loss are also typically high in fiber.

It is very important to try to maintain as consistent a schedule as possible when treating a diabetic. By feeding your pet the same food (content and quantity), and giving him/her insulin at the same times every day, you will ensure consistency. You can vary by as much as an hour and a half, but be as consistent as possible. Owners of diabetic pets should notify their veterinarian if they notice any changes in their pet’s water intake, appetite, urination or energy level.


Pets with diabetes mellitus can live long, happy lives. Good communication between the pet parent and the veterinarian is crucial to successful management of diabetes.


Animal Specialty Group

DVM, Diplomate American College of Veterinary Internal Medicine

Dr. Rhonda Schulman has authored numerous book chapters and journal articles, and has lectured nationally on a variety of medicine topics, most extensively in pulmonology and endocrinology.

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