Diabetes Mellitus

What Is It?

Everything we eat is eventually digested into smaller building blocks, such as sugars, amino acids, and fatty acids. These are absorbed from the gastrointestinal tract into the bloodstream. Insulin, a hormone produced by the pancreas, is required for animals and people to use these nutrients for energy, growth, and repair. Insulin moves these substances from the bloodstream into the body’s cells; in other words, it ‘opens the gates’ of the cells so the building blocks can be used by the body. Without enough insulin, the sugar or glucose in the blood cannot get into the cells. As a result, glucose builds up in the bloodstream and spills out in the urine. This combination of high blood glucose (hyperglycemia) and glucose in the urine (glucosuria) is called diabetes mellitus.

Diabetes mellitus is an extremely common disease in people, dogs, and cats. There are two forms of diabetes. The form in which an individual has absolutely no insulin is known as insulin-dependent diabetes mellitus (IDDM), type I diabetes, or juvenile-type diabetes. The other form occurs when an individual has insulin but either does not have enough or has a condition that interferes with insulin function. This type is known as non-insulin-dependent diabetes mellitus (NIDDM), type II diabetes, or adult-onset diabetes. In people, approximately 10% have IDDM, whereas 90% have NIDDM. Approximately 50-70% of cats and nearly 100% of dogs have insulin-dependent diabetes mellitus (IDDM).


The diagnosis of diabetes mellitus begins with a complete medical history and a thorough physical examination. Most dogs are between 4 and 14 years old, with females affected approximately twice as frequently as males. In cats, the disease occurs most frequently in neutered males greater than 6 years of age.

As the glucose from the blood spills into the urine, it pulls water with it, leading to the formation of large amounts of dilute urine (polyuria). Most owners notice that their once housetrained dog begins urinating in the house or their cat starts urinating outside of the litter box. To compensate for the increased urination, diabetic animals need to drink more water (polydipsia). In addition, without insulin to move glucose into the cells, the cells begin to ‘starve’. In response to this ‘starvation’, the pet feels the need to eat larger quantities of food (polyphagia). The cells still don’t have access to the sugars being consumed and additional messages are sent out to break down the body’s fat and muscle reserves for energy. This is seen as weight loss and muscle wasting. rinking excessively, urinating excessively, eating excessively, and losing weight are the first signs of diabetes mellitus. Other clinical signs may include a loss of appetite, weakness, depression, and abdominal pain. If these signs go unnoticed, pets may develop cataracts, neuropathies, or may become severely ill (ketoacidosis).

Your veterinarian may wish to perform a complete blood count (CBC), a serum chemistry profile, thyroid function tests, and a urinalysis in order to diagnose diabetes, screen for concurrent diseases, and establish a baseline prior to treatment. Because secondary infections are common, a urine culture may also be warranted.


There is no cure for diabetes, but as in humans, we can do our best to control the disease. The primary goals of therapy are the elimination of clinical signs, reduction of blood glucose fluctuations, and maintenance of normal or near-normal blood glucose concentrations. This can be accomplished through proper insulin administration, diet, and the prevention or control of concurrent diseases.


A proper diet is essential for controlling diabetes in all animals. In some cats, a prescription diet can actually alleviate the need for insulin. Dietary therapy is aimed at 1) eliminating obesity, 2) maintaining consistency in the timing and caloric content of each meal, and 3) minimizing fluctuations in glucose. In dogs, high fiber diets are used because they slow intestinal glucose absorption and help to regulate glucose levels. Hill’s Prescription Diet w/d can be used for this purpose. For cats, we typically prefer a high protein diet such as Purina Veterinary Diet DM or Hill’s m/d. For dogs, it is ideal to feed a meal twice per day during the time of insulin administration. In cats, it is ideal to feed canned food at the time of insulin administration, but many owners also leave dry food out for cats to eat throughout the day.


The type of insulin and the daily dose are tailored to meet the needs of each animal. Some pets require once daily administration, while most animals require insulin twice per day. Please be aware that the initial stabilization of your pet’s diabetes may require several changes in the type and dosage of insulin. This stabilization period can often last 4-8 weeks.

After the initial diagnosis, your pet may be hospitalized for a maximum of 1-2 days to begin insulin therapy and reverse some of the metabolic abnormalities. The goal of this initial stay is NOT to achieve perfect control. An initial dose of insulin will be chosen and your pet will be sent home with instructions for insulin handling and administration. During the initial week, the pet’s body begins to adjust to insulin therapy. This is best done in the home environment where appetite and activity level are more normal than in a clinic setting. After 1 week, your veterinarian will perform a blood glucose measurement and/or curve to determine whether the insulin dose needs to be increased or decreased.

Following are some guidelines for the handling and administration of insulin to your pet. Measuring and administering insulin will be explained and demonstrated to you. Do not leave the clinic until you have practiced giving an injection and are confident of performing treatments at home.

Insulin handling

  • Refrigerate your pets’ insulin. Accidentally leaving it out once in a while will not cause a loss of activity, but extended room temperature storage will. Keep the insulin out of direct sunlight.
  • Insulin precipitates during storage. Gently mix the insulin before use by rocking or rolling the bottle between your hands. DO NOT SHAKE the bottle. Shaking can break the insulin proteins and change the effectiveness of that bottle. Please note: If your pet is on Vetsulin insulin, shaking is recommended to ensure proper mixing, but that is unique to Vetsulin insulin.

Insulin syringes

  • It is very important that the syringes that you purchase match the concentration of the insulin that you are using. You need U-100 syringes for NPH and glargine and U-40 syringes for Vetsulin or Prozinc insulin.
  • Syringes should be used only once! Please dispose of used syringes safely. You can place used syringes in a solid plastic container marked ‘Sharps’ and place it in your garbage.

Insulin administration

  • We will teach you how to administer insulin to your pet.
  • Giving pets, especially dogs, treats at the same time as their injection will make it a positive experience for your pet. Some will even come remind you when it is time for their treatment!

Management notes

  • If, when you are administering insulin, you slip or your pet moves at the wrong moment and part of the dose winds up in the fur instead of under the skin, do not try to estimate how much insulin your pet received. It is generally safest to just get back on track at the next dose than to risk overdosing.
  • If you are not available to give the insulin within 2 hours before or after the usual time, just skip that insulin dose and give the next dose at the next standard time. It is safer to skip one dose than to give two doses too closely together. However, do not routinely skip doses!
  • If your pet refuses to eat for any reason, do not give the insulin without calling the clinic first. Giving a full dose of insulin to a non-eating animal can lead to a hypoglycemic crisis. Depending on the circumstances, we may recommend giving a reduced dose or bringing your pet in for a blood glucose check and/or additional bloodwork. If you are unable to reach our clinic, a good rule of thumb is to give ½ the normal amount of insulin if your pet ate little or nothing during the previous 12 hours. Once your pet’s appetite is back to normal, you can start to give the standard dose again. Seek medical attention immediately if there are other signs of illness.


When regulating a diabetic animal’s blood glucose level, the goal is to maintain the blood glucose between approximately 80 and 250 mg/dl throughout the day. Ideally, the normal range (80-150 mg/dl) is attained, but this is often very difficult.

As discussed above, after being on insulin for a week, you will schedule a blood glucose check with your veterinarian. Please feed your pet a normal meal in the morning and give the prescribed insulin dose. Discuss with your veterinarian what time your pet should arrive at the clinic. During the first 4-8 weeks following diagnosis, your pet’s blood glucose may need to be checked several times in order to find the correct insulin dose and type for your pet. Your veterinarian may also perform a fructosamine level on your pet. This is a blood test that indirectly measures blood glucose levels over the preceding 2-3 weeks.

Much of the monitoring of your diabetic pet is done by you at home. It is very important to monitor your pet’s water consumption, urine output, appetite, and energy level. Careful observation of these parameters at home will provide important information for your veterinarian in attempting to control your pet’s diabetes. In addition, it is crucial to monitor for life-threatening hypoglycemia. These signs may include seizures, coma, weakness, stumbling, depression, or ‘drunkenness’.

Your pet should have periodic blood glucose curves, chemistry profiles, and urinalyses performed to monitor how well the diabetes is regulated and to watch for the development of concurrent conditions such as urinary tract infections, liver disease, kidney disease, and Cushing’s disease. Your veterinarian will set up a monitoring plan that best fits your pet. If you are interested in testing your cat’s blood glucose levels at home, please discuss this with your veterinarian. There are two excellent websites: www.veterinarypartner.com and www.felinediabetes.com that describe how this can be accomplished. However, it is important that you consult with your veterinarian before altering your pet’s insulin dose – never change your pet’s dose without first discussing it with your veterinarian!


Hypoglycemia or low blood sugar can be one of the most life-threatening side effects of insulin administration. Always have a concentrated sugar solution such as Karo syrup or honey on hand. If your pet seems weak, confused, loses consciousness, stumbles, adopts a ‘glazed’ look in his or her eyes, or has a seizure, administer one to two teaspoons to small dogs and cats or 1-2 tablespoons to large dogs. Repeat this treatment every 10-15 minutes until your pet is able to eat on its own. If your pet is not responding, seek medical attention immediately.

Recurrence or persistence of clinical signs is the most common ‘complication’ in diabetic dogs and cats. This may be due to problems with technique of administering insulin; problems with the type, dose, or frequency of insulin administration; or problems with responsiveness to insulin caused by concurrent disease. Insulin resistance can be due to drugs, Cushing’s disease, diestrus or pregnancy (intact dogs), infection, inflammation, obesity, cancer, or diseases of the liver, kidneys, heart, or thyroid. Some animals may even produce antibodies to the insulin.

Cataracts develop in nearly 100% of dogs with diabetes mellitus within 6-24 months of diagnosis. Cataracts may be removed surgically to restore your dog’s vision. Consult with your veterinarian regarding the options for cataract removal.

If your pet’s diabetes goes uncontrolled, a condition called diabetic ketoacidosis develops. This is a condition in which the body produces acids called ketones in response to not having glucose available to the cells. Ketones can build up in the body and cause very life-threatening metabolic derangements.

Finally, diabetic animals are more susceptible to other health problems. Diabetes mellitus can cause an increased incidence of infection (especially bladder infections), slowed healing, gastrointestinal dysfunction, kidney disease, heart disease, pancreatitis, and nervous system disorders.

If you have any questions about diabetes mellitus in your pet, please consult with your veterinarian. We are here to help answer your questions and make the process as easy and understandable as possible. While treating a diabetic animal may not always seem easy, it can be very rewarding for both you and your pet.