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Diabetes Mellitus in Cats

Understanding Diabetes
Types of Diabetes
What Insulin Does for the Body
Classical Signs of Diabetes Mellitus
Diagnosing Diabetes
What It Means for Your Cat to be Diabetic
About Insulin
Spontaneous Remission


Treating a diabetic cat can often be a challenge. In some cats, it can be very difficult to maintain steady diabetic regulation. However, there are several important concepts that make this process much more likely to be successful.

  1. Consistency: Our goal is to find an appropriate dose of insulin that will last on a long-term basis. In order to do that, we must eliminate as many variables as possible. In other words, the more things that can stay the same from one day to the next, the easier it is to keep a diabetic regulated. Our goal is to give the same dose of insulin the same times each day, to feed the same food in the same quantities each day, to keep the activity level the same each day, and to keep your cat's stress level the same.
  2. Tight control is usually not necessary in cats. Human diabetics must maintain blood glucose values very close to normal at all times. If they don't, they will develop some disastrous complications of diabetes, such as loss of fingers, toes, feet, and hands, kidney failure, heart problems, and cataract formation. These complications are rare in diabetic cats. Therefore, as stated below, it is safer for a cat's blood glucose to be too high than too low.
  3. Hyperglycemia (high blood glucose) is almost always better than hypoglycemia (low blood glucose).
  4. As the dose of insulin goes up, the blood glucose goes down.
  5. Food intake causes the blood glucose to rise. Failure to eat may allow the blood glucose to fall below normal.

The latter three above principles are applied as such: If you are not sure if you gave a dose of insulin or you are not sure if it was properly injected, do not give it again. If your cat does not eat, do not give insulin or give a lower dosage as directed by your veterinarian. If you must miss a dose or two of insulin (occasionally), do not be concerned. Your cat's blood glucose will get too high for a day or two, but that should not cause great problems.

Understanding Diabetes

There are two forms of diabetes in cats: diabetes insipidus and diabetes mellitus. Diabetes insipidus is a very rare disorder that results in failure to regulate body water content. Your cat has the more common type of diabetes, diabetes mellitus. This disease is fairly common, usually occurs in cats 5 years of age or older, and males are more commonly affected than are females, especially if they are overweight. Simply put, diabetes mellitus is a failure of the pancreas to produce insulin, and/or failure of the body to properly utilize any insulin that the pancreas DOES produce.

The pancreas is a small but vital organ that is located near the stomach. It has two significant populations of cells. One group of cells produces the enzymes necessary for proper digestion. The other group, called beta cells, produces the hormone called insulin.

Types of Diabetes

In cats, as in people, there are two types of diabetes mellitus. Both types are similar in that there is a failure to regulate blood sugar, but the basic mechanisms of disease differ somewhat between the two groups.

1. Type I, or Insulin Dependent Diabetes Mellitus, results from total or near-complete destruction of the beta cells. This is the most common type of feline diabetes. As the name implies, cats with this type of diabetes require insulin injections to stabilize blood sugar because their pancreas fails to produce insulin.

2. Type II, or Non-Insulin Dependent Diabetes Mellitus (NIDDM), is different because some insulin-producing cells remain. However, the amount produced is insufficient, there is a delayed response in secreting it, and/or the tissues of the cat's body are relatively resistant to it. These cats may be treated with an oral drug that stimulates the remaining functional cells to produce or release insulin in an adequate amount to normalize blood sugar. Alternatively, they may be treated with insulin. Cats with NIDDM may ultimately progress to total beta cell destruction and then require insulin injections.

What Insulin Does for the Body

The role of insulin is much like that of a gatekeeper. It stands at the surface of body cells and opens the door, allowing glucose to leave the blood stream and to pass inside the cells. Glucose is a vital substance that provides much of the energy needed for life, and it must work inside the cells. Without an adequate amount of insulin, glucose is unable to get into the cells. It accumulates in the blood, setting in motion a series of events that can ultimately prove fatal.

When insulin is deficient, the cells become starved for a source of energy. In response to this, the body starts breaking down stores of fat and protein to use as alternative energy sources. As a consequence, the cat eats more; thus, we have weight loss in a cat with a ravenous appetite. The body tries to eliminate the excess glucose by eliminating it in the urine. However, glucose (blood sugar) attracts water; thus, urine glucose takes with it large quantities of the body's fluids, resulting in the production of a large amount of urine. To avoid dehydration, the cat drinks more and more water. Thus, we have the four classical signs of diabetes:

Weight loss
Ravenous appetite
Increased water consumption
Increased urination

Diagnosing Diabetes

The diagnosis of diabetes mellitus is based on three criteria: the four classical clinical signs, the presence of a persistently high level of glucose in the blood stream, and the presence of glucose in the urine.

The normal level of glucose in the blood is 80-120 mg/dl. It may rise to 250-300 mg/dl following a meal or when the cat is very excited or stressed (as most are with veterinary visits). However, diabetes is the only common disease that will cause the blood glucose level to rise above 400 mg/dl. Some diabetic cats will have a glucose level as high as 800 mg/dl, although most will be in the range of 400-600 mg/dl.

To keep the body from losing its needed glucose, the kidneys do not allow glucose to be filtered out of the blood stream until an excessive level is reached. This means that cats with a normal blood glucose level will not have glucose in the urine. Diabetic cats, however, have excessive amounts of glucose in the blood, so it will be present in the urine.

The diagnosis of diabetes seems rather simple, and in most cats it is. However, some diabetic cats do not meet all the criteria. For these, another test called a blood fructosamine test is performed. This test is an indicator of what the average blood glucose level has been over the past few weeks. It minimizes the influence that stress and eating have on blood glucose levels and can be very helpful in understanding difficult cases that may be less straight forward in their diagnosis.

What It Means for Your Cat to be Diabetic

For the diabetic cat, one reality exists. Blood glucose cannot be normalized without treatment. Although the cat can go a few days without treatment and not get into a crisis, treatment should be looked upon as part of the cat's daily routine. Treatment almost always requires some dietary changes. Whether an individual cat will require oral therapy or insulin injections will depend on the individual cat's situation.

As for the owner, there are two very important implications: financial commitment and personal commitment.

When your cat is well regulated, the maintenance costs are minimal. The special diet, the oral medication, insulin, and syringes are not real expensive. However, the financial commitment can be significant during the initial regulation process and/or if complications arise.

At diagnosis, in some cases, your cat may need to be hospitalized for a few days to deal with any immediate crisis and to begin the regulation process. An "immediate crisis" exists if your cat is so sick that he or she has quit eating and drinking for several days. Cats in this state, called ketoacidosis, may require several days or more of hospitalization with quite a bit of laboratory testing. These cats are considered to be "complicated" diabetics. The ketoacidotic state is potentially life threatening, and is a medical emergency. With non-complicated (non-ketoacidotic) cats, however, no hospitalization is necessary, and your cat's diabetic regulation is done at home. At first, return visits are required every 14 - 21 days to monitor progress and diagnosis. It may take several months or more to achieve good regulation.

The financial commitment may again be significant if complications arise. We will work with you to achieve consistent regulation, but some cats are difficult to keep regulated. It is important that you pay close attention to our instructions related to administration of medication, to diet, and to home monitoring. Consistency is the key to prolonged regulation. The more you keep the medication, diet, and activity the same from one day to the next, the easier it will be to keep your cat regulated. Being aware of changes (increased or decreased) in your cat's water intake and urine output may also be helpful to us in assessing how well we may be regulating your cats diabetes.

Another complication that can arise is hypoglycemia or low blood sugar; if severe, it may be fatal. This may occur due to inconsistencies in treatment, because some cats can have a spontaneous remission of their disease, or because they may have spontaneous changes in insulin or oral diabetic drug requirements. This will be explained in subsequent paragraphs.

Your personal commitment to treating this cat is very important in maintaining regulation and preventing crises. Most diabetic cats require insulin injections twice daily, at about 12 hour intervals (some variation in this interval is very acceptable). They must be fed the same food in the same amount on pretty much the same schedule every day. If you are out of town, your cat must receive proper treatment while you are gone. These factors should be considered carefully before deciding to treat a diabetic cat.


As mentioned, the key to successful treatment is consistency. Your cat needs consistent administration of medication, consistent feeding, and a stable, stress-free lifestyle. To best achieve this, it is preferred that your cat live indoors. Indoor living removes many uncontrollable variables that can disrupt regulation.

The first step in treatment is to alter your cat's diet. At the present time, a high protein, low carbohydrate diet seems to be the best diet for most diabetic cats. There is a therapeutic (prescription) diet available through veterinarians formulated specifically for diabetic cats that meets these requirements. In some cats, this diet alone may help to achieve even better diabetic control and lower insulin requirements. Diets that are high in fiber historically have been used because they are generally lower in sugar and slower to be digested. This means that the cat does not have to process a large amount of sugar at one time. Which of these diets is best for your cat will be discussed with you by your veterinarian. In general wet or canned food is preferred over dry food because the carbohydrate content is lower in canned foods.

Your cat's feeding routine is also important. It desirable to monitor how much food is eaten each day. We realize that if you have more than one cat, this may be difficult, but please make an effort, as this is part of the home monitoring that should occur. Many owners give canned food twice daily with the insulin injections to make sure the cats are eating.

The second step in treatment is to use a drug to control (lower) control blood glucose levels. The choices are to give insulin injections or to give an oral drug. Occasionally both are used. Both have advantages and disadvantages.

Generally, most cats, even if started on oral drugs, sooner or later end up needing insulin. For this and other reasons (see below), insulin injections are often the first treatment choice. This approach is to replace the hormone that is missing or made in inadequate amounts. Although many people are initially uncomfortable with the thought of giving injections, for most cats insulin injections are easier than giving tablets.

This is generally our preferred way to treat diabetic cats, especially if they are as follows:

  1. Cats that do not take tablets well.
  2. Cats belonging to owners who cannot give tablets.
  3. Cats that fail to respond to the oral drugs.
  4. Cats that have been ketoacidotic. As mentioned above, ketoacidosis is also known as "complicated" diabetes, and this is a life-threatening condition that requires immediate treatment with insulin in a veterinary hospital setting, no time to "fiddle around with" oral drug treatment, which may take several weeks for effects to be seen.
  5. Cats belonging to owners who find injections easier to give than tablets. (Most cats are in this category. This is not because pills are hard to give but because injections are very easy to give.)

Many people are initially fearful of giving insulin injections. If this is your initial reaction, consider these points:

  1. Insulin does not cause pain when it is injected.
  2. The injections are made with very tiny needles that your cat hardly feels.
  3. The injections are given just under the skin in areas in which it is almost impossible to cause damage to any vital organ. Please do not decide whether to treat your cat with insulin until we have demonstrated the injection technique. You will be pleasantly surprised at how easy it is.

The second option for treatment is the use of a tablet that lowers blood glucose. It is estimated that as many as 25% of diabetic cats have Type II (non insulin-dependent) diabetes. This may be especially true in the very earliest stages of diabetes before the blood sugar levels are real high. This means that they may be treated with oral medication instead of insulin injections. There is no reliable, practical test to know if your cat is a Type I or Type II diabetic. Therefore, we must place your cat on an initial dose of glipizide or glyburide, and/or other hypoglycemic/insulin-sensitizing drugs, for 4-8 weeks. Blood glucose levels are checked every few weeks for a couple of months until it is determined whether or not a response is occurring. If response occurs and blood sugar levels decline, this treatment is continued until it is no longer effective. That may be for many years or for only a few months, depending on the progression of destruction of the beta cells in the pancreas. If minimal or no response occurs within a few weeks, your cat will then need to be put on insulin injections.

As mentioned previously, one disadvantage to treating with tablets is that some cats only have a temporary response. The tablets function by stimulating the existing beta cells so they work more efficiently. Many diabetic cats have a gradual decline in the number of functioning beta cells as time passes. This means that a time will come in many cats when the tablets are no longer effective.

About Insulin

Insulin comes in an airtight bottle that is labeled with the insulin type and the concentration. Before using, mix the contents. It says on the label to roll it gently, not shake it. The reason for this is to prevent foam formation, which will make accurate measuring difficult. Shaking the insulin too vigorously may also cause breakage of the insulin crystals, which may make the insulin less effective. Some of the types of insulin used in cats settle out of suspension in a few hours. If it is then not mixed properly prior to administration, dosing will not be accurate. Therefore, the trick is to roll it vigorously enough to mix it without creating foam. Since bubbles can be removed (as described later), it is more important to mix it well than to worry too much about foam formation.

Insulin is a hormone that will lose its effectiveness if exposed to direct sunlight or high temperatures. It should be kept in the refrigerator, but it should not be frozen. It is not ruined if left out of the refrigerator for a day or two as long as it is not exposed to direct sunlight. However, we do not advise this. Insulin is safe as long as it is used as directed, but it should be kept out of reach of children.

Several types of insulin are used in cats. Some are made for use in humans and obtained from regular pharmacies. Protamine zinc insulin (PZI) is made specifically for cats and is available from veterinarians. PZI has a concentration of 40 units of active insulin crystals per milliliter of fluid. Thus it is called U40 insulin. Insulins made for humans have a concentration of 100 units per milliliter and are called U100 insulins. This is important to know because there are two types of insulin syringes, U40 syringes and U100 syringes. They are made to be used with their respective types of insulin and should not be interchanged or improper dosing may occur.

Drawing up Insulin

Have the syringe and needle, insulin bottle, and cat ready. Then, follow these steps:

  1. Remove the guard from the needle, and draw back the plunger to the appropriate dose level.
  2. Carefully insert the needle into the insulin bottle.
  3. Inject air into the bottle; this prevents a vacuum from forming within the bottle.
  4. Withdraw the correct amount of insulin into the syringe.

Before injecting your cat with the insulin, verify that there are no air bubbles in the syringe. If you get an air bubble, draw twice as much insulin into the syringe as you need. Then withdraw the needle from the insulin bottle and tap the barrel of the syringe with your finger to make the air bubble rise to the nozzle of the syringe. Gently and slowly expel the air bubble by moving the plunger upward.

When this has been done, check that you have the correct amount of insulin in the syringe. The correct dose of insulin can be assured if you measure from the needle end, or "0" on the syringe barrel, to the end of the plunger nearest the needle.

Injecting Insulin

The steps to follow for injecting insulin are:

  1. Hold the syringe in your right hand (switch hands if you are left-handed).
  2. Have someone hold your cat if possible while you pick up a fold of skin from somewhere along your cat's back with your free hand.
  3. Quickly push the very sharp, very thin needle through your cat's skin. This should be easy and painless. However, take care to push the needle through only one layer of skin and not into your finger or through two layers of skin. The latter will result in injecting the insulin onto your cat's hair coat or onto the floor. The needle should be directed parallel to the backbone or angled slightly downward.
  4. To inject the insulin, place your thumb on the plunger and push it all the way into the syringe barrel.
  5. Withdraw the needle from your cat's skin. Immediately place the needle guard over the needle and discard the needle and syringe.
  6. Stroke your cat to reward it for sitting quietly.
  7. The needle and syringe should then be safely placed into your sharps container. When your container is full, securely close the lid and place it in your regular garbage and pick up a new sharps container. (These can also be purchased through many local pharmacies.)

It is neither necessary nor desirable to swab the skin with alcohol to "sterilize" it. There are four reasons:

  1. Due to the nature of the thick hair coat and the type of bacteria that live near the skin of cats, brief swabbing with alcohol or any other antiseptic does not really kill all the bacteria.
  2. Because a small amount of alcohol can be carried through the skin by the needle, it may actually carry bacteria with it into the skin.
  3. The sting caused by the alcohol can make your cat dislike the injections.
  4. If you have accidentally injected the insulin on the surface of the skin, you will not know it. If you do not use alcohol and the skin or hair is wet following an injection, the injection was not done properly.

Although the above procedures may at first seem complicated and somewhat overwhelming, they will very quickly become second nature. Your cat will soon learn that once or twice each day it has to sit still for a few seconds. In most cases, a reward of stroking results in a fully cooperative cat that rarely even needs to be held. Many owners will give the insulin injection just as the cat starts eating. most cats won't even flinch!!


It is necessary that your cat's progress be checked on a regular basis. Monitoring is a joint project on which owners and veterinarians must work together.

Home Monitoring

You can monitor your cat for signs of diabetes. Home monitoring of diabetic signs is very important, and we recommend that it be done in conjunction with blood glucose monitoring (the latter is usually performed in the hospital though some owners can accomplish this at home). To monitor for diabetic signs, you need to be constantly aware of your cat's appetite, weight, water consumption, and urine output. You should be feeding a constant amount of food each day, which will allow you to be aware of days that your cat does not eat all of it or is unusually hungry after the feeding. You should weigh your cat at least twice monthly. It is best to use the same scales each time. A baby scale works best for this, because it measures weight to the ¼ pound, and some will even measure to the ounce. (A weight increase or decrease of a few ounces may be significant in a diabetic cat!). If you have several cats that eat together and use the same litter box, monitoring weight is the best because it is specific to this one cat. (Baby scales can often be purchased at large discount stores, baby stores, EBay, through your veterinarian, etc.)

When your cat’s diabetes is controlled, his or her water intake and urine output should be at or near the level that it was prior to development of diabetes. If your cat is well-regulated on a given level of insulin, and then starts to show signs again of increased thirst and urination, or if a change in appetite or weight is noted, we should see the cat at that time for blood testing.

Monitoring of Blood Glucose

Along with home monitoring of diabetic signs by the owner, determining the level of glucose in the blood is the most accurate means of monitoring diabetic regulation. Blood monitoring of glucose and fructosamine levels needs to be done somewhat frequently until proper diabetic regulation is attained after initial diagnosis. Once your cat is well regulated, blood glucose/fructosamine monitoring needs only to be done about every 3-6 months. It should also be done at any time the clinical signs of diabetes are present. As mentioned above, some owners (and their cats!) are amenable to doing the majority of the blood glucose monitoring at home via tiny ear pricks. We would be happy to go over this procedure with you. If done properly, most cats are very accepting of this, and it eliminates the stress that the cat experiences with trips to the hospital for frequent blood glucose checks, as well as the associated expense.

Timing is important when the blood glucose is determined. Since eating will elevate the blood sugar for a few hours, it is usually best to test the blood at least 2-3 hours after eating, and at the time when the insulin is reaching its peak level of activity (which varies by type of insulin).

Your cat’s first blood sugar check should be 10-14 days after initiating insulin treatment. We usually check this and subsequent samples at 6-8 hours after the insulin injection has been given. This is because in most cats, the morning and evening insulin injection reach their peak activity time at 6-8 hours post injection so blood sugar is therefore at its lowest points of the day at these two times. Checking the blood sugar at the insulin’s peak activity time is one way that helps us to determine whether or not the dosage of insulin is appropriate. In most diabetic cats, we also run a “fructosamine” blood test at least every 3-6 months. This test gives us an indication of what the average blood sugar levels have been running during the previous 2-3 weeks. (This is a test that can’t be reliably performed via an in-home ear prick – it requires that a larger sample of blood be sent to an outside lab). In some cats the insulin does not peak at 6-8 hours post injection – it may be much sooner or much later. In these cases, even further testing may be needed to determine exactly when the insulin is peaking and, therefore, the appropriate dosage and number of daily insulin injections that need to be given.


Hypoglycemia means low blood sugar. If it is below 40 mg/dl, it can be life-threatening. Signs of hypoglycemia include lethargy, wobbly gait, glazed eyes, twitching, and ultimately seizures. (The latter three signs occur if the blood glucose reaches extremely low levels.) Hypoglycemia occurs under three conditions:

  1. If the insulin dose is too high. Although most cats will require the same dose of insulin for long periods of time, it is possible for the cat's insulin requirements to change. Other common causes for change are a reduction in food intake and an increase in exercise or activity. The reason for feeding before the insulin injection is so you can know when the appetite changes. If your cat does not eat, skip that dose of insulin. If only half of the food is eaten just give a half dose of insulin. Always remember that it is better for the blood sugar to be too high than too low.
  2. If too much insulin is given. This can occur because the insulin was not properly measured in the syringe or because double doses were given. You may forget that you gave it and repeat it, or two people in the family may each give a dose. A chart to record insulin administration will help to prevent the cat being treated twice.
  3. If your cat has a spontaneous remission of the diabetes. This is a poorly understood phenomenon, but it definitely occurs in about 20% of diabetic cats. They can be diabetic and on treatment for many months, then suddenly no longer be diabetic. Since this is not predictable and may happen quite suddenly, a hypoglycemic crisis ("insulin shock") is often the first indication.

The most likely time that a cat will become hypoglycemic is the time of peak insulin effect (6-8 hours after an insulin injection). When the blood glucose is only mildly low, your cat may have no outward signs at all. If the glucose level is moderately low, your cat may be very tired and less responsive. You may call your cat and get no response. In these cases, the blood glucose will rise, and your cat will return to normal. Since many cats sleep a lot during the day, these important signs may be easily missed. Watch for them; they may be the first sign of impending problems. If you see these, please bring in your cat for blood testing (or do the ear prick glucose check at home).

If your cat is slow to recover from this period of lethargy, you should give your cat Karo or corn syrup (1 tablespoon by mouth) or feed one packet of a semi-moist cat food. If there is no response in 15 minutes, repeat the corn syrup or the semi-moist food. If there is still no response, contact us immediately for further instructions. (Diabetic cats should not be fed semi-moist foods except for this situation.) (Note: Even for those owners who do not do ear prick blood glucose checks at home, if your cat is acting hypoglycemic but you can’t ‘prove’ it by checking his or her blood sugar, go ahead and administer the Karo syrup; remember, even if you’re ‘wrong’, and the ‘signs’ that you observed weren’t related to low blood sugar, it’s still safer as a general rule to have blood sugar that is too high versus too low – i.e., it’s best to err on the side of caution!)

If severe hypoglycemia occurs, a cat may have seizures or lose consciousness. This is an emergency that needs to be treated with intravenous administration of glucose. Should signs of severe low blood sugar occur, apply Karo or corn syrup right away to your cat’s gums (use a blunt knife or spoon so as not to get bit if your cat is having a seizure) – then immediately bring your cat into Cat Hospital of Chicago (or the Animal Emergency and Critical Care Center or Chicago Veterinary Emergency Service, if after hours).

Spontaneous Remission

Spontaneous remission means that a diabetic cat is no longer diabetic. This is a phenomenon that happens in about 15-20% of diabetic cats. Unfortunately, it can happen rather suddenly so a hypoglycemic crisis may be created because the owner does not realize remission has occurred and continues to give the normal amount of insulin.

For a few days after remission occurs, the cat is able to make emergency amounts of glucose as the blood glucose level falls to dangerously low levels. It does so by converting glycogen, a product stored in the liver, to glucose and releasing it into the bloodstream. However, at some point in time the glycogen stores are depleted and it can no longer respond; a hypoglycemic crisis then occurs.

When spontaneous remission occurs, the cat may be normal (non-diabetic) for a few weeks, for many months, or even a few years). However, diabetes will often return because these cats have limited ability to make insulin. Therefore, you should watch for the typical signs of diabetes then contact us for insulin instructions.

If you have questions, or would like further information, please don’t hesitate to contact us. You might also find helpful a website designed by lay people as a “support system” for diabetic cat owners. It is an excellent, informative, user-friendly site. Their website address is www.felinediabetes.com.

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