Heartworms in Cats

Heartworms are 9-11” long worms that live in a cat’s heart or in the arteries going to the lungs (pulmonary arteries). Although they occur commonly in dogs, most people do not consider them a problem for the cat. However, recent studies of cats with heart and respiratory diseases have found an incidence of heartworms that is far greater than we previously thought.

Dogs vs. Cats

Dogs often have 30 or more worms present; however, many cats have only 2-4 adult worms in the heart. Adult heartworms live 3-4 years in the dog’s heart but only 1-2 years in circulation; cats usually do not produce any immature worms. Dogs have changes in the shape of the heart and pulmonary arteries as seen on radiographs (x-rays). Their pulmonary arteries become tortuous (curved) and enlarged. However, cats will usually have normal shaped hearts with pulmonary arteries that are blunted, presumably related to partial obstructions due to the presence of adult worms. Dogs usually have a persistent rise in eosinophils, a normal white blood cell that can be associated with parasitic infection. Cats have an eosinophil increase that occurs briefly within a few months of infection. By the time clinical signs are present, most cats have a normal eosinophil count.

Contributing Factors

Because heartworms are transmitted by mosquitoes, the disease is more common in areas of the country with large numbers of mosquitoes. Infection with feline leukemia virus or feline immunodeficiency virus does not seem to increase the risk that cats will get heartworms, even though they adversely affect the immune system.


The southeastern United States has a relatively high incidence of heartworm disease for both dogs and cats when compared to other parts of the country, although heartworm disease may occur anywhere that mosquitoes can survive. There is no apparent difference between infection rates between male and female cats, although male cats generally have greater numbers of worms than female cats. Although indoor cats might be at less risk for heartworm infection, more recent studies indicate that infection rates between indoor and outdoor cats are about the same. All ages are at risk for infection.


Heartworms are transmitted through mosquitoes. When an infected mosquito bites a cat, it deposits baby heartworms (larvae). The larvae migrate and mature for several months, ending up in the right side of the heart and the pulmonary arteries. They mature into adult heartworms about 6 months from the time they enter the cat. Shortly thereafter, they begin to release immature heartworms, known as microfilaria. Microfilaria live in the cat’s blood for about one month. They are ingested by mosquitoes feeding on the cat. (However, most mosquitoes acquire microfilaria by feeding on heartworm-infected dogs.) Because of their life cycle, it is necessary for a cat to be bitten by a mosquito to be infected with heartworms. Heartworms are not transmitted directly from one cat to another nor from a dog directly to a cat.


There are several methods used in diagnosing heartworms; unfortunately, none are 100% reliable so a combination of tests is often needed. The diagnostic sequence usually progresses as follows:

Clinical Signs

One of the difficult things about diagnosing heartworms is that there are no consistent clinical signs. The most common signs are coughing and rapid breathing. However, both can be caused by several other diseases. Other common clinical signs include weight loss and vomiting, also common in other diseases. Some cats seem to be normal, then die suddenly. This happens due to a reaction within the lungs to the young heartworms or when dead or live heartworms enter the pulmonary arteries and obstruct the flow of blood to the lungs.

Blood Tests

1. There are two tests that are proving to be very helpful in diagnosing heartworms. The heartworm antibody test determines that the cat’s immune system has been exposed to heartworms. A positive test may indicate that an active infection is present. However, cats who have had heartworms but whose heartworms have died will also have antibodies for an unknown period of time. This test is very sensitive, so it is used first. However, if it is positive the next test is performed.

2. The next test is the heartworm antigen test. This detects the presence of the adult female heartworms. It is very specific, but not as sensitive. This means that a positive test indicates that heartworms are present, but a negative test does not mean that they are absent. Because the cat must have at least 2 adult female worms present to make this test positive, a negative test may mean that the cat may only have a small number of worms or that all the worms present are male.

In summary, a diagnosis of heartworms is confirmed if both the antibody and antigen tests are positive.

It should be noted that most veterinarians are able to perform an in-hospital test to detect heartworm antigen in dogs. However, the canine test is not as sensitive as the test for cats so using it will result in more false negative results.

3. Blood can be tested for the presence of microfilaria. However, less than 10% of cats with heartworms have microfilaria in their blood, and the microfilaria are only present for 1-4 weeks. Therefore, a negative test means little.

4. Cats suspected of heartworms can be tested for their level of eosinophils. Eosinophils are normal white blood cells that occur in increased numbers when certain parasites are present. They are elevated in the presence of heartworms, but this elevation only occurs for a few months. In addition, cats with intestinal parasites (“worms”) and allergies also commonly have increased eosinophil counts.


Radiographs (x-rays) permit us to view the size and shape of the heart. They also allow us to measure the diameter of the pulmonary arteries. Many cats with heartworms have an increase in the size of the pulmonary arteries; they may suddenly come to an apparent stop (blunted) on their way to the lungs due to worms obstructing them. However, many cats with heartworms have no abnormal findings on their radiographs, especially early in the infection.

An angiogram is an x-ray study in which contrast material (dye) is injected into the heart or veins and seen as it goes through the pulmonary arteries. This illuminates the arteries so they can be seen better. There is some risk to this procedure so it is not used often.


An ultrasound machine produces an image of internal organs and structures without the use of radiation. It is a testing procedure that is becoming more and more common in veterinary practices. With it, one is able to view the internal structures of the heart and the pulmonary arteries. In some cats, the actual heartworms can be seen; this finding confirms the presence of heartworms. However, in many cats the worms are not seen.


Dogs that have heartworms are treated with a drug this is safer than the originally used drug and is very effective. However, there is no such drug for cats. Another problem is that when the heartworms die they pass through the pulmonary arteries to the lungs. This can result in sudden death. Thus, we have a dilemma when a cat is diagnosed with heartworms. One of two choices must be made:

1. Treat with the drug designed for dogs. However, this is a drug that is unproved for cats and is not recommended as the chance for complications and side effects, including death, is high.

2. Treat the symptoms of heartworm disease and hope the cat outlives the worms. Since heartworms live in a cat for about two years, several months of treatment is needed. When cats are in a crisis, they are treated with oxygen, corticosteroids (“cortisone”) to relieve the reaction occurring in the pulmonary arteries and lungs, and, if needed, drugs to remove fluid from the lungs (diuretics). When they are stable, they are treated continuously or periodically with corticosteroids. However, the threat of an acute crisis or sudden death always exists.

Indoor Cats

Logically, we would think that indoor-only cats would be very unlikely to get heartworms. However, studies of heartworm infected cats consistently show that about one-third of them live indoors all of the time. As strange as this seems, there is a good explanation. The cat is not the natural host for heartworms. Because of this, the cat’s immune system is able to kill the larval stages most of the time. Each time a cat is exposed and successfully kills heartworm larvae, some immunity is develops. This is a type of natural vaccination. However, indoor-only cats do not get this constant exposure so their natural immunity is not as good. When a mosquito gets into the house and bites the cat, this cat is actually more likely to develop heartworms than most outdoor cats.


It is strongly recommended that dogs take drugs to prevent heartworms. It is well accepted that even dogs in cold climates should be on heartworm prevention at least part of the year. The monthly chewable tablet, HeartGard* and the monthly topical products, Revolution*, Advantage MultiTM, are good insurance against a disastrous disease. Therefore, prevention of heartworms is safe and easy. The reasons that heartworm prevention should be considered for your cat are:

1. Diagnosing heartworms is not as easy in cats as in dogs. A simple and reliable in-hospital blood test is not yet available, and the tests that are most reliable must be sent to an outside laboratory. Often, radiographs or ultrasound studies are needed to confirm the diagnosis. Many cats are diagnosed with an autopsy following sudden death.

2. Heartworms are not nearly as common in cats as they are in dogs. However, they are probably more common than we realize. As we look more aggressively for heartworms in cats with better and better tests, we expect to find that the incidence is greater than we thought in the past.

3. There is not a good treatment for heartworm-infected cats. Effective drugs are not available, and cats that seem to be doing well may die suddenly. Treating heartworm infections in cats is risky, and not treating these cats is just as risky. If they are cured of the disease, it takes about two years.

4. Cats given heartworm prevention drugs have not shown signs of toxicity. Since they only have to be given once each month and since they are formulated so that cats will eat them readily, administration is not a problem (in most cats). There is a wide margin of safety, even in kittens as young as 6 weeks of age.

5. Exposure to mosquitoes is all that is required for transmission. Cats do not have to be exposed to cats or dogs infected with heartworms.

Heartworm Disease in Dogs

Heartworm disease (dirofilariasis) is a serious and potentially fatal disease in dogs. It is caused by a worm called Dirofilaria immitis.

Heartworms are found in the heart and large adjacent vessels of infected dogs. The female worm is 6 to 14 inches (15 to 36 cm) long and 1/8 inch (5 mm) wide; the male is about half the size of the female. One dog may have as many as 300 worms.

How Heartworms get into the Heart

Adult heartworms live in the heart and pulmonary arteries of infected dogs. They have been found in other areas of the body, but this is unusual. They survive up to 5 years and, during this time, the female produces millions of young (microfilaria). These microfilaria live in the bloodstream, mainly in the small blood vessels. The immature heartworms cannot complete the entire life cycle in the dog; the mosquito is required for some stages of the heartworm life cycle. The microfilaria are therefore not infective (cannot grow to adulthood) in the dog–although they do cause problems.

As many as 30 species of mosquitoes can transmit heartworms. The female mosquito bites the infected dog and ingests the microfilariae during a blood meal. The microfilariae develop further for 10 to 30 days in the mosquito and then enter the mouthparts of the mosquito. The microfilariae are now called infective larvae because at this stage of development, they will grow to adulthood when they enter a dog. The mosquito bites the dog where the haircoat is thinnest. However, having long hair does not prevent a dog from getting heartworms.

When fully developed, the infective larvae enter the bloodstream and move to the heart and adjacent vessels, where they grow to maturity in 2 to 3 months and start reproducing, thereby completing the full life cycle.


Canine heartworm disease occurs all over the world. In the United States, it was once limited to the south and southeast regions. However, the disease is spreading and is now found in most regions of the United States and Canada, particularly where mosquitoes are prevalent.


The disease is not spread directly from dog to dog. An intermediate host, the mosquito, is required for transmission. Spread of the disease therefore coincides with the mosquito season. The number of dogs infected and the length of the mosquito season are directly correlated with the incidence of heartworm disease in any given area.

It takes a number of years before dogs show outward signs of infection. Consequently, the disease is diagnosed mostly in 4 to 8 year old dogs. The disease is seldom diagnosed in a dog under 1 year of age because the young worms (larvae) take up to 7 months to mature following establishment of infection in a dog.

Effects on the Dog

Adult worms: Adult worms cause disease by clogging the heart and major blood vessels leading from the heart. They interfere with the valve action in the heart. By clogging the main blood vessels, the blood supply to other organs of the body is reduced, particularly the lungs, liver and kidneys, leading to malfunction of these organs.

Most dogs infected with heartworms do not show any signs of disease for as long as 2 years. Unfortunately, by the time signs are seen, the disease is well advanced. The signs of heartworm disease depend on the number of adult worms present, the location of the worms, the length of time the worms have been present, and the degree of damage to the heart, lungs, liver, and kidneys from the adult worms and the microfilariae.

The most obvious signs are: a soft, dry, chronic cough, shortness of breath, weakness, nervousness, listlessness, and loss of stamina. All of these signs are most noticeable following exercise, when some dogs may even faint.

Listening to the chest with a stethoscope will often reveal abnormal lung and heart sounds. In advanced cases, congestive heart failure may be apparent and the abdomen and legs will swell from fluid accumulation. There may also be evidence of weight loss, poor condition, and anemia.

Severely infected dogs may die suddenly during exercise or excitement.

Microfilariae (Young worms): Microfilariae circulate throughout the body but remain primarily in the small blood vessels. Because they are as wide as the small vessels, they may block blood flow in these vessels. The body cells being supplied by these vessels are deprived of the nutrients and oxygen normally supplied by the blood. The lungs and liver are primarily affected.

Destruction of lung tissue leads to coughing. Cirrhosis of the liver causes jaundice, anemia, and general weakness because this organ is essential in maintaining a healthy animal. The kidneys may also be affected and allow poisons to accumulate in the body.


In most cases, diagnosis of heartworm disease can be made by a blood test that can be run in the veterinary hospital. Further diagnostic procedures are essential, in advanced cases particularly, to determine if the dog can tolerate heartworm treatment. Depending on the case, we will recommend some or all of the following procedures before treatment is started.

Serological test for antigens to adult heartworms: This is a test performed on a blood sample. It is the most widely used test because it detects antigens (proteins) produced by adult heartworms. It will be positive even if the dog does not have any microfilaria in the blood; this occurs about 20% of the time. Dogs with less than five adult heartworms will not have enough antigen to turn the test positive, so there may be some false negative results in early infections. Because the antigen detected is produced only by the female worm, a pure population of male heartworms will give a false negative, also. Therefore, there must be at least 5 female worms present for the most common test to be positive.

Blood test for microfilariae: A blood sample is examined under the microscope for the presence of microfilariae. If microfilariae are seen, the test is positive. The number of microfilariae seen gives us a general indication of the severity of the infection. However, the microfilariae are seen in greater numbers in the summer months and in the evening, so these variations must be considered. Approximately 20% of dogs do not test positive even though they have heartworms because of an acquired immunity to this stage of the heartworm. Because of this, the antigen test is the preferred test. Also, there is another microfilarial parasite which is fairly common in dogs; on the blood smear, these can be hard to distinguish from heartworm microfilariae.

Blood chemistries: Complete blood counts and blood tests for kidney and liver function may give an indirect indication of the presence of heartworm disease. These tests are also performed on dogs diagnosed as heartworm-infected to determine the function of the dog’s organs prior to treatment.

Radiographs (X-rays): A radiograph of a dog with heartworms will usually show heart enlargement and swelling of the large artery leading to the lungs from the heart. These signs are considered presumptive evidence of heartworm disease. Radiographs may also reveal the condition of the heart, lungs, and vessels. This information allows us to predict an increased possibility of complications related to treatment.

Electrocardiogram: An electrocardiogram (EKG) is a tracing of the electric currents generated by the heart. It is most useful to determine the presence of abnormal heart rhythms.

Echocardiography (Sonogram): An echocardiogram allows us to see into the heart chambers and even visualize the heartworms themselves. Although somewhat expensive, this procedure can diagnose heartworms when other tests fail.


There is some risk involved in treating dogs with heartworms, although fatalities are rare. In the past, the drug used to treat heartworms contained arsenic so toxic effects and reactions occurred somewhat frequently. Now a newer drug is available that does not have the toxic side effects of the old one. We are able to successfully treat more than 95% of dogs with heartworms.

We see some dogs with advanced heartworm disease. This means that the heartworms have been present long enough to cause substantial damage to the heart, lungs, blood vessels, kidneys, and liver. A few of these cases will be so far advanced that it will be safer to just treat the organ damage rather than risk treatment to kill the worms. Dogs in this condition are not likely to live more than a few weeks or months.

Treatment to kill adult worms: An injectable drug to kill adult heartworms is drug is given for two days. It kills the adult heartworms in the heart and adjacent vessels.

Complete rest essential after treatment: The adult worms die in a few days and start to decompose. As they break up, they are carried to the lungs, where they lodge in the small blood vessels and are eventually reabsorbed by the body. This is a dangerous period, and it is absolutely essential that the dog be kept quiet and not be allowed to exercise for 1 month following treatment. The first week after the injections is very critical because the worms are dying. A cough is noticeable for 7 to 8 weeks after treatment in many heavily infected dogs.

Prompt treatment is essential if the dog has a significant reaction in the weeks following the initial treatment, although such reactions are not common. If a dog shows loss of appetite, shortness of breath, severe coughing, coughing up blood, fever, and/or depression, you should notify us. Response to antibiotics, cage rest, and supportive care, such as intravenous fluids, is usually good in these cases.

Treatment to kill microfilaria: Approximately 1 month following treatment to kill the adults, the dog is returned to the hospital for administration of a drug to kill microfilariae. Your dog needs to stay in the hospital for the day. Seven to ten days later a test is performed to determine if microfilariae are present. If they have been all killed, the treatment is complete. If there are still some present in the blood, treatment for microfilariae is repeated.

In some cases, the heartworm infection is “occult,” meaning that no microfilariae were present. In this case, a follow-up treatment at one month is not needed.

Other treatments: In dogs with severe heartworm disease, it may be necessary to treat them with antibiotics, special diets, diuretics to remove fluid accumulations, and drugs to improve heart function prior to treatment for the heartworms.

Dogs with severe heart disease may need lifetime treatment for the failing heart, even after the heartworms have been killed. This includes the use of diuretics, heart drugs, aspirin, and special low salt, low protein diets.

Response to treatment: Dog owners are usually pleasantly surprised at the change in their dog following treatment for heartworms, especially if the dog had been showing signs of heartworm disease. The dog has a renewed vigor and vitality, improved appetite, and weight gain.


When a dog has been successfully treated for heartworms, you cannot sit back and relax because dogs can be reinfected. Therefore, it is essential to begin a heartworm prevention program. There are two drugs that can we recommend to use to prevent heartworm infection. They are HeartGard* and Interceptor*, are chewable tablets that are given only once monthly. All four products are very safe and very effective. Their costs are similar. One of these should be started immediately after the treatment is completed.

Diabetes Mellitus in Cats

Treating a diabetic cat can be a challenge. Some cats just never seem to stay regulated. 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 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, and cataract formation. These complications do not happen to diabetic cats. Therefore, as stated above, it is better for the blood glucose to be too high than too low.

3. Hyperglycemia (high blood glucose) is 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 allows 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 if it was properly injected, do not give it again. If your cat does not eat, do not give insulin. 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 will 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 seen on a fairly regular basis, usually in cats 5 years of age or older. Simply put, diabetes mellitus is a failure of the pancreas to regulate blood sugar.

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.

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 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. 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 is performed called fructosamine. This test represents the average blood glucose level for the past two weeks. It minimizes the influence that stress and eating have on blood glucose levels and can be very helpful in understanding difficult cases.

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 vary.

As for the owner, there are two 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 expensive. However, the financial commitment can be significant during the initial regulation process and if complications arise.

In some cases, your cat will be hospitalized for a few days to deal with the immediate crisis and to begin the regulation process. The “immediate crisis” is only great if your cat is so sick that it has quit eating and drinking for several days. Cats in this state, called ketoacidosis, may require a week or more of hospitalization with quite a bit of laboratory testing. Otherwise, the initial hospitalization may be only for a day or two to get some testing done and to begin treatment. At that point, your cat goes home for you to administer medication. At first, return visits are required every 5-7 days to monitor progress. It may take a month 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.

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 or because some cats can have a spontaneous remission of their disease. 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. They must be fed the same food in the same amount on 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 lives indoors. Although that is not essential, indoor living removes many uncontrollable variables that can disrupt regulation.

The first step in treatment is to alter your cat’s diet. Diets that are high in fiber are preferred 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. If your cat is overweight, a reducing-type diet is fed until the proper weight is achieved, then your cat is switched to a high fiber maintenance food.

Your cat’s feeding routine is also important. The average cat prefers to eat about 10-15 times per day, one mouthful at a time. This means that food is left in the bowl at all times for free choice feeding. Fortunately, this is the best way to feed a diabetic cat. However, it is also 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.

The second step in treatment is to use a drug to control (lower) control blood glucose levels.

Insulin injections are usually the first choice because this approach is to replace the hormone that is missing or made in inadequate amounts.

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.

Insulin Therapy and Administration

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. Some of the types of insulin used in cats settle out of suspension in a few hours. If it is not mixed properly dosing will not be accurate.

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 obtained 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 must not be interchanged or improper dosing will 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 while you pick up a fold of skin from somewhere along your cat’s back with your free hand (pick up a different spot each day).
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) Be aware that some communities have strict rules about disposal of medical waste material so don’t throw the needle/syringe into the trash until you know if this is permissible. If it is not, we can dispose of them for you.

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 minutes. In most cases, a reward of stroking results in a fully cooperative cat that eventually may not even need to be held.


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

Your part can be performed in one or both of two ways. The first way is to monitor your cat for signs of diabetes. To do this, 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 well for this. 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.

If possible, you should develop a way to measure water consumption. The average 10 pound (4.5 kg) cat should drink no more than 7 1/2 oz. (225 ml) of water per 24 hours. Since this is highly variable from one cat to another, keeping a record of your cat’s water consumption for a few weeks will allow you to establish what is normal for your cat. Another way to measure water consumption is based on the number of times it drinks each day. When properly regulated, it should drink no more than four times per day. If this is exceeded, you should take steps to make an actual measurement.

Urine output can be measured by determining the amount of litter that is scooped out of the litter box. This is a little less accurate if you have more than one cat that uses the litter box, but it can still be meaningful. The best way to measure litter is to use a clumping litter and scoop it into a sealable container. After a few weeks you will be able to know the normal rate at which the jar fills. Too rapid filling will indicate that your cat’s urine production has increased.

Any significant change in your cat’s food intake, weight, water intake, or urine output is an indicator that the diabetes is not well controlled. We should see the cat at that time for blood testing.

The second method of home monitoring is to determine the presence of glucose in the urine. If your cat is properly regulated, there should be no glucose present in the urine.

There are several ways to detect glucose in urine. You may purchase urine glucose test strips in any pharmacy. They are designed for use in humans with diabetes, but they will also work in the cat. The use of special non-absorbing kitty litter permits you to dip the test strip into urine in the litter box. Aquarium gravel, Styrofoam packing “peanuts,” and commercial non-absorbing litter can be used. Since these are not ideal litter materials, they are best used on a periodic basis.

Another method is as follows:

1. Put about 1 tablespoon of wet litter in a small cup. (A clay type litter is required; clumping litter will not work.)
2. Add about 1 tablespoon of tap water to the litter and stir.
3. Dip a urine glucose test strip into the liquid and read it according to the directions on the bottle.
4. The results will be about half of the actual urine glucose amount because of the dilution of the added water.

If glucose is detected by either method, the test should be repeated the next two days. If it is present each time, we should see your cat for a blood test.

Monitoring of Blood Glucose

Determining the level of glucose in the blood is the most accurate means of monitoring. This should be done about every 3-4 months if your cat seems to be well regulated. It should also be done at any time the clinical signs of diabetes are present or if glucose is detected in the urine for two consecutive days.

Timing is important when the blood glucose is determined. Since eating will elevate the blood sugar for several hours, it is best to test the blood at least 6 hours after eating.

When testing the blood we want to know the highest and lowest glucose readings for the day. The highest reading should occur just before an injection of insulin is given. The lowest should occur at the time of peak insulin effect. This is usually 5-8 hours after an insulin injection, but it should have been determined during the initial regulation process. Therefore, the proper procedure is as follows:

1) Feed your cat its normal morning meal then bring it to hospital immediately. If you cannot get it to the hospital within 30 minutes, do not feed it. In that situation, bring its food with you.
2) Bring your cat to the hospital early in the morning without giving it insulin.
3) A blood sample will be taken immediately, then we will give insulin and feed your cat if it did not eat at home.
4) A second blood sample will be taken at the time of peak insulin effect.

If your cat gets excited or very nervous when riding in the car or being in the hospital, the glucose readings will be falsely elevated. If this occurs, it is best to admit your cat to the hospital the morning (or afternoon) before testing so it can settle down for testing the next day. Otherwise, the tests give us limited information.


Hypoglycemia means low blood sugar. If it is below 40 mg/dl, it can be life-threatening. 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. However, the most 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 happens quite suddenly, a hypoglycemic crisis (“insulin shock”) is usually the first indication.

The most likely time that a cat will become hypoglycemic is the time of peak insulin effect (5-8 hours after an insulin injection). When the blood glucose is only mildly low, the cat will be very tired and unresponsive. You may call it and get no response. Within a few hours, the blood glucose will rise, and your cat will return to normal. Since many cats sleep a lot during the day, this important sign is easily missed. Watch for it; it is the first sign of impending problems. If you see it, please bring in your cat for blood testing.

If your cat is slow to recover from this period of lethargy, you should give it 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. (Note: Diabetic cats should not be fed semi-moist foods except for this situation.)

If severe hypoglycemia occurs, a cat will have seizures or lose consciousness. This is an emergency that can only be reversed with intravenous administration of glucose. If it occurs during office hours, come in immediately. If it occurs at night or on the weekend, call our emergency phone number for instructions.

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 blood stream. However, at some point in time the glycogen stores are depleted and it can no longer respond; a hypoglycemic crisis then occurs.

When it occurs, the cat may be normal for a few weeks or for many months. However, diabetes will almost always return because these cats have limited ability to make insulin.


1) Read and reread this material so that you understand the specifics of proper regulation and how to recognize and treat hypoglycemia.

2) Give the first injection of insulin of _____units at about _________ AM/PM.

3) Return for a glucose curve at about the same time as you normally give insulin in 5-7 days. Allow your cat to eat through the night or feed it that morning and immediately bring it to the hospital. Do not give insulin, but bring it with you. (If it will take more than 30 minutes to drive to the hospital, call for instructions on feeding.)

4) Feed your cat one of the foods mentioned above.

Cruciate Ligament Injury and Repair in Dogs

The knee (stifle) joint of the dog is one of the weakest in the body. Just as athletes (football players, in particular) frequently suffer knee injuries, the dog also has knee injuries. The knee joint is relatively unstable because there is no interlocking of bones in the joint. Instead, the two main bones, the femur and tibia, are joined with several ligaments. When severe twisting or excessive extension of the joint occurs, the most common injury is a rupture of the anterior cruciate ligament (ACL). When it is torn, instability occurs that allows the bones to move in an abnormal fashion in relation to one another. When this happens, it is not possible to bear weight on the leg without it collapsing.

Contributing Factors

A special note is appropriate concerning the dog’s weight. Obesity or excessive weight can be a strong contributing factor in cruciate rupture. The ligament may become weakened due to carrying too much weight; this causes it to tear easily. Obesity will make the recovery time much longer, and it will make the other knee very susceptible to cruciate rupture. If your dog has a weight problem, there are prescription diets that can be used to assist weight reduction.


Rupture of the ACL is most common in middle aged and older dogs, particularly those that are overweight house pets.


In younger dogs, rupture of the ACL is usually the result of trauma to the stifle joint. In some cases, the ligament may only partially tear; however, this will eventually lead to complete tearing of the ligament. When ACL rupture occurs in older dogs, it is most frequently initiated by a progressive degenerative change in the ligament with eventual total rupture.

Clinical Signs

Dogs with a ruptured ACL are usually lame and may refuse to bear weight on the affected leg. Eventually, most dogs become more willing to bear weight but some degree of lameness remains.


The most reliable means of diagnosing this injury is to move the femur and tibia in a certain way to demonstrate the instability. This movement is called a “drawer sign.” It can usually be demonstrated with the dog awake. If the dog is very painful, has very strong leg muscles, or is uncooperative, it may be necessary to use sedation in order to examine the joint adequately.


Correction of ACL rupture requires surgery. A skilled surgeon can stabilize the joint so it functions normally or near normally. If surgery is not performed within a few days to a week, arthritic changes will begin that cannot be reversed, even with surgery.

Occasionally, the injury that causes a ruptured anterior cruciate ligament will also result in tearing of one or both of the menisci or “cartilages.” At the time of surgery, these are examined and removed if necessary.


Following proper and prompt surgical correction, the joint is sound again. Most dogs walk and run without any lameness; however, some have either a mild limp or lameness associated with cold and damp weather.

Occasionally, a dog that has a ruptured cruciate ligament will become sound (will no longer limp), even if surgery is not performed. However, progressive, degenerative arthritis will develop and result in lameness a few months later. Once these degenerative changes are established, the lameness cannot be corrected, even with surgery.