Pet Connections

Diabetes Mellitus of Dogs and Cats

By: Tracey Peterson, DVM, DACVIM                                                                                                                        

Internal Medicine Specialist at Pittsburgh Veterinary Specialty and Emergency Center (PVSEC)

The initial clinical signs are innocent enough.  Brittany, your five year old maltese, urinated in the living room.  She has always been well house trained so this is puzzling.  Now that you think about it, you have noticed that you are refilling her water bowl more frequently.  Maybe it’s the hot weather or maybe she’s stressed about the home renovations.  She is still active and interactive.  Her appetite is still good.  In fact, her appetite is great.  She never misses a meal and is more eager for treats than she ever has been.  This goes on for a few weeks.  She has more accidents in the house. You just can seem to keep her water dish full.  Even though she has a ravenous appetite, you notice somehow, some way, Brittany appears to be losing weight.  Increased water consumption and urination frequency with weight loss in the face of a normal to increased appetite are all telling signs Brittany has developed diabetes mellitus.

Diabetes mellitus occurs when the pancreas fails to produce enough insulin for the body’s daily requirements.  Insulin is the hormone required to move glucose from the blood into the cells where it is used for energy.  Without insulin, regardless of the caloric intake, the body’s tissues are in a constant state of starvation, resulting in weight loss.  Without insulin, glucose cannot be shuttled into the cells.  As a consequence, there is an excessive amount of glucose in the blood stream.  The kidneys are responsible for excreting this excess glucose resulting in excessive urination and thirst.  If left undiagnosed and untreated, diabetes mellitus can have severe, life-threatening metabolic consequences.

Unlike many other endocrine (hormonal) diseases, diabetes mellitus is relatively easy for your veterinarian to diagnose at the initial evaluation.  In dogs and cats, the diagnosis of diabetes mellitus is made when there is a documented elevation in blood glucose with a concurrent glucose in the urine.   Certain drugs and stress can cause an elevation in a blood glucose reading but rarely result in glucose leakage into the urine.  If there is any question whether your dog or cat has diabetes mellitus, before starting treatment, additional testing may be recommended.  This may be re-checking the blood and urine glucose in a few days or submitting an additional blood test called a fructosamine.  Fructosamine is a marker of glucose concentration over the previous 1-3 weeks and should not be affected by drugs or stress.  An elevation in the fructosamine level supports the diagnosis of diabetes mellitus.

Unlike people, dogs diagnosed with diabetes mellitus cannot be managed with oral medication and or diet and exercise.  Dogs are considered to be insulin dependent.  They will require a subcutaneous injection of insulin every 12 hours for the rest of their life.   There are both veterinarian and human insulin therapy options that can be used for diabetic management.  Your veterinarian can discuss these options in detail.  Diet is a critical factor in canine diabetic management.  It is more important to make sure your dog is consistently eating a full meal so insulin can safely be administered. 

Cats are not small dogs.  Cats with diabetes mellitus do have similarities to people with diabetes mellitus.  Although the majority of cats (70%) diagnosed with diabetes required daily insulin injections, some can be managed with diet alone.  There are commercially available, specially formulated high protein, low carbohydrate diets that can regulate the blood glucose.  In addition, some cats initially diagnosed with insulin dependent diabetes mellitus can achieve diabetic remission and have their disease managed by diet alone.  This remission can be transient or permanent.  It is important to note, although feeding a diabetic diet can help with diabetic management, it is not 100% necessary.  There are many cats happily eating grocery store brand food that still have good management of their diabetes.  As with dogs, for those cats with insulin dependent diabetes, it is most important for your cat to be consistently eating so insulin can safely be administered.  Diet and insulin options for your cat can be discussed in detail with your veterinarian. 

Although at home blood glucose monitoring for your diabetic pet is an option, scheduling a follow up appointment with your veterinarian for a blood glucose curve and fructosamine is recommended.  This involves feeding and administering insulin at the regular time then obtaining a blood glucose reading every 2 hours. The goal of a blood glucose curve is to determine the current dose of insulin’s duration of effect and when the peak effect occurs.  Therapy recommendations can be made based on these results.  It is critical to never increase an insulin dose based on a single blood glucose reading as a single high reading could mean your pet is over-regulated (receiving too much insulin) and not under-regulated (receiving too little insulin).  This is because if the blood glucose is too low, the body quickly adjusts to increase the blood glucose.  If the single reading is taken during the time of adjustment, this high glucose reading would be incorrectly interpreted to mean a higher dose of insulin is necessary. Inappropriately increasing the insulin dose could result in life-threatening hypoglycemia (low blood sugar).  An insulin dose should never be adjusted without the advisement of your veterinarian.

What does a diagnosis of diabetes mellitus mean for my pet’s quality of life and longevity of life? Often the prognosis depends on the owner’s commitment to treating the disease.  Concurrent illness, like kidney disease or pancreatitis, can make good regulation challenging.  Administering too much or too little insulin can have life-threatening consequences.  Dogs with diabetes mellitus can develop cataracts, which will require treatment.  That being said, if diagnosed early and treated and monitored appropriately, a good quality of life can be maintained for years with this disease. 

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