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Diabetes Mellitus in Pets

Diagnosing and Treating Diabetes Mellitus in Dogs and Cats

By: Tabitha Hutton, DVM, MTR, DACVIM (SAIM), Internal Medicine Specialist at Saint Francis Veterinary Center

November is National Diabetes Month, raising awareness of an important disease in humans that can also occur in animals. Diabetes mellitus (DM) mainly develops in dogs and cats, though it can rarely be seen in other species (ferrets, horses, etc.). DM is a disease process that revolves around the availability and activity in the body of a hormone called insulin. Insulin’s main job is to allow glucose (sugar) that comes from food entry into the cells of the body. If glucose cannot enter a cell, it cannot be used for energy. The result is that the body’s cells “starve in the face of plenty” causing glucose to build up to high levels in the bloodstream, spilling into the urine, but the glucose cannot “fuel” the body’s tissues.

Insulin is produced by an organ called the pancreas that is located in the belly near the stomach and small intestines. The cells in the pancreas that produce insulin are called beta cells. DM can develop from one of two main causes:

1)     Type I DM: a decrease or lack of insulin production by the pancreas due to death of beta cells.

2)     Type II DM: a decrease of insulin production by the beta cells and/or insulin resistance (decreased ability of the body to respond to insulin properly).

Type I DM is most common in dogs; cats can suffer from type I or type II DM.


Risk factors for DM in dogs include genetics (certain breeds are predisposed) and pancreatitis (a disease that causes inflammation and destruction of the pancreas). The main risk factor for DM in cats is obesity, though genetics and/or pancreatitis can also play a role. Certain medications (prednisone, other glucocorticoids, megestrol acetate) and concurrent diseases (Cushing’s syndrome, acromegaly, heat cycles in intact females) can risk development of type II DM in both species.


Signs of DM include excessive drinking, excessive urination, ravenous appetite, and weight loss. The tests required for an initial diagnosis of DM are relatively simple: documentation of persistently high blood glucose along with detecting glucose spilled into the urine is sufficient in most cases. Sometimes other tests are needed (more commonly for cats), such as testing urine for glucose at home and/or a fructosamine test (which reflects average blood glucose levels over a period of time).


While the diagnosis of DM is fairly straightforward, additional testing is recommended in most cases, to screen for concurrent diseases that may be causing the DM as well as some complications that can result. This typically includes full routine blood work, a urinalysis and urine culture, and in some cases, x-rays and/or ultrasound. Periodic urine cultures are especially important, as DM makes animals especially prone to urinary tract infections, due to all the glucose in the urine.

Although lifestyle changes such as diet change and weight loss may be significantly beneficial in many cases (especially for cats), almost all animals will require insulin therapy. There is even some evidence to support that early intervention with certain types of insulin therapy in cats may result in a temporary or permanent remission of DM in some cases! Insulin is provided as an injection under the skin, usually twice daily after a meal. The veterinarian will then recommend monitoring to help judge whether the insulin dose is sufficient or not. In many patients, it is not difficult to find an insulin dose that is appropriate for the pet. In some cases, however, regulation of the disease may be more challenging. In these cases, further testing may be recommended, or the veterinarian may refer the pet to be evaluated by a board certified internal medicine specialist.

Dietary changes do play a significant role, particularly in cats. Current thinking on this topic is that a higher protein, lower carbohydrate diet can help promote better blood glucose regulation in cats. In general, canned food tends to be higher in protein and lower in carbohydrate relative to dry food, so often a canned food will be recommended. High dietary fiber may also play a role in regulating blood glucose levels, and is sometimes used for diabetic dogs. There are a variety of prescription diets available for DM in both dogs and cats that can be obtained through your veterinarian if he/she deems it indicated. Maintaining a healthy weight is also an important way to improve regulation of a pet’s DM. A weight loss plan for a pet should always be initiated and monitored in conjunction with recommendations from a veterinarian to ensure safe but effective weight loss.

There are some oral medications on the market that have been used for some diabetic cats in lieu of insulin therapy, but as most of these medications are less effective than insulin and fraught with side effects, they are not typically the first recommended treatment. Oral medications are not used in the treatment of DM in dogs.


Complications of DM can occur, and the pet must be monitored for these regularly. One of the most frequent is urinary tract infection, which if left untreated, can lead to more serious complications such as a kidney infection. Other types of infections, such as skin and ear, can also occur. Cataracts, leading to blindness, are very common in diabetic dogs. Ketoacidosis is a potentially life-threatening complication of DM that is typically discovered in a previously undiagnosed diabetic pet. It is a significant metabolic derangement that requires hospitalization for aggressive fluid and electrolyte therapy, as well as close blood test monitoring (glucose, electrolytes, pH) along with initiation of insulin therapy. Finally, hypoglycemia (low blood sugar) can occur from an insulin overdose. This can occur if the wrong dose is accidentally given, if the pet did not eat well for another reason (illness, stress, abrupt diet change), or if the insulin dose was recently increased. Hypoglycemia can lead to weakness, incoordination or even seizures, and may require hospitalization for intravenous sugar supplementation.

Though some complications can be severe, and treatment of a pet with DM requires dedicated care from both owner and veterinarian for the life of the pet, most pets with DM can go on to live a good quality life.