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Diabetes In Dogs And Cats

Diabetes Mellitus is a disease by which the islet cells of the pancreas (cells responsible for secreting the hormone insulin into systemic circulation) lack the ability to secrete adequate amounts of insulin, or, insulin receptors on body cells are refractory to the effects of insulin when secreted; or both. Insulin plays an important role in the body regulating blood sugar (glucose) in response to ingestion of carbohydrates. When blood glucose levels spike in the blood following a carbohydrate rich meal, insulin is secreted by the pancreas to trigger the body cells to take up the excess blood glucose out of systemic circulation and store it in the cells. This keeps blood glucose levels in check, while providing glucose for the cells, which is their primary source of energy. When insulin is deficient from defective pancreatic islet cells, or, if body cell receptors are refractory to the effects of insulin, the result is chronically high blood glucose, diabetes mellitus.

Diabetes Mellitus literally translates to “sweet urine.”  The reason for this is that when blood glucose level exceeds 180 (normal for dogs and cats is 80-130), excess glucose in teh blood stream begins to get excreted by the kidneys into the urine.  Thus, the blood glucose of 180 or higher is know as exceeding the “renal threshold.”

The physiological effects of this disease are many. First, since body cells are not effectively taking up glucose, they are depleted of glucose and starved for energy. Over time, this leads to cell death and profound weightloss. Second, the excess blood glucose causes physiological problems. Excess glucose exceeding the renal threshold ends up passing through the kidneys and gets urinated out. Glucose attracts water, and therefore pulls excess water out of the body, causing chronic dehydration. This is the reason many diabetic dogs and cats drink excessive amounts of water. When the glucose rich urine collects in the urinary bladder, lower urinary tract infections often occur, because bacteria are attracted to the glucose.

In the brain, with individual cells that make up brain tissue, called neurons, being especially sensitive to the inability to take up glucose for energy, cells become compromised and begin to die when deprived of blood glucose. In combination with high levels of blood glucose that occur with diabetes mellitus and osmotic and electrolyte disturbances, disorientation, seizure, coma, and even brain death can occur in unregulated canine and feline diabetics.

At the level of the blood vessels, inflammatory disease of the walls of the blood vessels can occur in cases of unregulated diabetes called vasculitis. Vasculitis may lead to disturbances in circulation, vascular pain, and clot formations.

Brain is not the only central nervous system component that may be harmed by diabetes. Peripheral nerves may also be adversely affected by unregulated diabetes as high levels of blood glucose can lead to inflammation of these nerves, a condition known as neuropathy, a potentially painful and debilitating consequence.

Chronically high blood glucose as the result of diabetes, taxes the kidneys which can in turn can lead to kidney failure.   Diabetes adversely affects the metabolism of the lenses of the eyes, commonly leading to premature cataracts. This is an especially prevalent result of diabetes in dogs, which can severely compromise their vision.

Diagnosis is obtained through blood test and urinalysis. On general chemistry, high blood glucose is hallmark for diabetes mellitus and there are often concurrent electrolyte disturbances. On urinalysis, glucose is often found in the urine, which is never normal and clearly indicative of diabetes. Often, concurrent urinary tract infections are also discovered.

In consideration for treatment, there are significant differences in management of the diabetic cats versus diabetic dogs. With dogs being far more sensitive to the adverse effects of high blood glucose (vascular disease, peripheral nerve disease, cataracts, etc.), like people, it is important to try to regulate them as tightly as possible. With cats, on the other hand, since they are as a species more resistant to the adverse effects of high blood glucose, and given that stress (such as that cause by being in a veterinary clinic…) can have profound influence on blood glucose levels in cats, a more loosely regulated approach is generally favored. Therefore, our approach to regulating diabetes in each species is usually quite different.


95% of diabetic dogs have Type I insulin dependent diabetes.  This can occur from inherited genetic predisposition to diabetes or due to a severe bout of pancreatitis that the patient may have recovered from but was left with permanent damage to the islet cells of the pancreas that are responsible for secreting insulin in response to dietary carbohydrates.  This means that while dietary and glycemic controlled diets are integral in properly regulating diabetic dogs, the vast majority of diabetic dogs will require life long insulin administration.

In dogs, there are several choices for types of insulin to choose from. My top choices are human based insulin brands, Novolan and Humulin N, as they are reasonably priced, can be obtained easily at most human pharmacies, and have shown to be comparably effective and consistent as any other insulin on the market for dogs in my experience.  There are other more costly insulin options, such as PZI, Lantus, and Vetsulin; but given the efficacy of and ease of availability of Novolan and Humulin N, I do not see the point of incurring the additional expense of these other options.

When first treating a diabetic dog with insulin, it is important to be mindful that the response to insulin is very individual, with a huge variation in blood glucose from one patient to the next from a given insulin dose. For this reason it is difficult to impossible to predict the proper insulin dose for a diabetic dog without doing what is called a blood glucose curve. This is when a conservative dose of insulin is administered, and the blood glucose levels are measured once every two to three hours. The insulin dose is adjusted according to these readings, and the patient is sent home on the appropriate dose, which is typically arrived at within 2-3 days in hospital.

Following the initial blood glucose curve, I typically follow up with a fructosamine level in 3 weeks. This gauges the body’s average response to insulin over a 2-3 week period. This is a more hands off method to monitor the blood glucose than a curve and is appropriate at this stage. The insulin dose is adjusted accordingly and the fructosamine is repeated every three weeks until adequate regulation is achieved. Once proper regulation is obtained, I typically have the patient come in once every 6 months for follow up fructosamine analysis, as well as to weigh the dog and get updates from the owner as to the water intake and urine output.


Oppositely to dogs, 95% of diabetic cats have Type II non-insulin dependent diabetes.  That means that in the case of cats, it is diet and obesity that likely led to their diabetes as the result of resistance to their body’s own insulin or a fatigued pancreas no longer capable of secreting sufficient amounts insulin to regulate blood glucose metabolism.  This also means that with proper diet and insulin regulation, there is a potential that cats may achieve diabetic remission and no longer require insulin (generally about 1 in 6 cats, somewhat dependent on the type of insulin selected – see below).

With cats, the initial response to a given insulin dose is also individual and arriving at the right dose can be challenging at first, just like in dogs. However, given the profound fluctuations in blood glucose that can occur from travel and in hospital stress in cats, keeping them in the hospital for a glucose curve is not accurate and is ill-advised from my view. A more hands off approach is favored.

Another reason that a more hands off monitoring schedule for diabetic cats is preferred, is that cats are generally more tolerant to the adverse effects causes by spikes in blood glucose than dogs and people are.  Thus, we do not see the same frequency and magnitude of diabetes complications such as peripheral vascular disease, diabetic peripheral and central neuropathy, kidney disease, cataracts, etc.  That is not to say that these complications do not occur as the result of unchecked diabetes in cats, however, we have found that attempting to regulate diabetic cats too tightly can lead to more problems than transient mild to moderate spikes in blood glucose that may occur in more loosely regulated cat.

Regarding the choice of insulin for cats, Novolan and Humulin N unfortunately generally do not have a long enough duration of activity sufficient to provide all day regulation of diabetic cats.  There are three main insulin options currently being favored for diabetic cats in veterinary medicine, and each have their pros and cons: Protamine Zinc Insulin (PZI), Vetsulin, and Lantus.


PZI is a bovine (cattle) derived insulin whose duration of activity works well for diabetic cats.  This insulin generally offers peak activity at 6 hours post injection, after which the blood glucose will gradually increase until reaching its peak concentration in the blood stream once again at 12 hours post injection.  At the latter time, another insulin injection is due, so this insulin ultimately is a twice daily administered insulin.

I generally recommend the ultra-loose approach with cats where they do not spend any appreciable amount of time in clinic.  The ultra-loose approach to diabetic regulation in cats with PZI insulin begins with a conservative insulin dose of 0.5 Units per kg of body weight, two times daily. I then have the cat return in one week for a quick blood glucose test, timed to be performed about 12 hours following the morning insulin injection. Good regulation using the ultra-loose approach would be blood glucose falling between 300-350 at this time. If the number does not fall within this range, then the insulin dose is adjusted and a blood glucose test is repeated in this fashion in one week…and so on and so forth until regulation is achieved. Once regulation is achieved, then a 12 hour post morning insulin injection blood glucose test is performed once every 3 months. Patient’s weight is also closely monitored, as are clinical updates from the owner, namely water intake and urine output.

While it is not the most expensive option, the main drawback to PZI insulin is the cost, currently retailing for $125-$150 a vial which generally lasts about 1 month.


Of the three insulin types I listed for feline diabetic, this one is my favorite from a strictly therapeutic point of view.  The reason for this is the consistency of Lantus in keeping steady state insulin activity for a 12 hour duration (as opposed to other insulins whose activity peak at 6 hours then taper off over the following 6 hours) and subsequent steady blood glucose levels.  Lantus insulin also imparts the best potential for diabetic cats to go into diabetic remission with approximately 20% of diabetic cats regulated with Lantus effectively being weaned off dependence on insulin.

My ultra-loose approach to regulating with Lantus is similar to that of PZI, but a 6 hour post injection blood glucose reading is done.  Ideal regulation would be a 6 hour post injection blood glucose of 100-200.

The big drawback to Lantus insulin is its high cost, at the time of this article costing in upwards of $200-$250 per vial that generally lasts about one month.  That is a staggering cost for many cat owners, but if it is not cost prohibitive, in my opinion Lantus is the best best insulin for diabetic felines.


Vetsulin is a porcine (pig) derived zinc insulin that has an efficacy and duration of activity quite similar to PZI insulin.  For this insulin, I typically use the ultra-loose approach to regulation just I like my approach to PZI (see above).  Of the three insulin choices, this one is generally the most cost effective, retailing for about $85 a vial.  Vetsulin is a veterinary only insulin and can only be purchased in veterinary clinics.

The prognosis for diabetes mellitus is typically good with reasonably good owner compliance, as well as the absence of other complicating systemic disease. In cats, as discussed earlier, some diabetics can go into what is called diabetic remission, where the body becomes increasingly less dependent on insulin until it is no longer needed. As previously mentioned, Lantus insulin seems to lead to remission in cats more than the other types of insulin available for use in cats. Dietary concerns are also important for diabetic cats. An ultra low carbohydrate diet gives the best opportunity to optimally regulate diabetic cats, while also increasing their likelihood of remission.

I do not like low carbohydrate in dogs, however, as it tends to cause more problems than benefit. Instead, I favor diets that are well balanced and carbohydrate controlled, where dietary carbohydrates are derived from complex carbs.

The most common complication and potentially dangerous event for diabetics on insulin, is what is known as a diabetic crash. This sometimes occurs for no apparent reason following the normal administration and dose of insulin, however, factors that prevent the patient from eating normal amounts on a given day can make the typically normal amount of insulin excessive, leading to a dangerous drop in blood glucose. For this reason, it is ideal to time two times daily meals around the insulin injections. This can be a bit more challenging in cats than in dogs, as many cats prefer to graze on freely offered food rather than have discrete meals.

The consequences of such a sudden drop in blood sugar can range from lethargy and weakness, to seizure, coma, and even death. For this reason, it is advisable that owners of diabetic dogs and cats have at their disposal, sugary syrup, such as maple syrup or karo syrup. If diabetic crash is suspected, the owner should rub a generous amount of one of these sweet syrups onto the gums to quickly raise the blood glucose level, and get the patient to a vet as soon as possible.


Roger L. Welton, DVM
Founder and Chief Editor,
President, Maybeck Animal Hospital

Article updated 1/24/2018

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