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Diabetes mellitus (DM) is a disease process involving either an absolute or relative insulin deficiency resulting in hyperglycemia.

Diabetes Mellitus.

  • Type I DM is comparable to insulin dependent diabetes mellitus (IDDM) in humans. It is characterized by beta cell destruction (in the pancreas) leading to absolute insulin deficiency. This usually occurs via cell-mediated autoimmune processes and is associated with multiple genetic predispositions and poorly defined environmental factors. It results in low insulin concentrations with impaired insulin secretion following a glucose load. Treatment requires insulin injections. Type I DM is the most common form of DM in dogs.

  • Type II DM is similar to non-insulin dependent diabetes (NIDDM) in humans and is characterized by an impaired ability to secrete insulin as well as insulin resistance. Triggering causes include obesity, genetics, and insular amyloid deposition. Some cases can be managed with dietary therapy and oral hypoglycemics while others require insulin. Type II DM currently is thought to account for the majority of cases of feline DM.

  • Type III DM is a condition whereby medications or concurrent insulin antagonistic diseases (hyperadenocorticim/Cushing’s disease, acromegaly, diestrus) interfere with insulin action and cause glucose intolerance, which can lead to DM. It is similar to impaired glucose tolerance in humans and is initially characterized by hyperinsulinemia. This type of DM may resolve or become overt depending on the situation.
  • The peak incidence of DM in dogs occurs at 6 - 9 years of age. Genetic predisposition has been noted in some breeds. The most common breeds are German Shepherds, Schnauzers, Beagles, and Poodles. Golden Retrievers and Keeshonds are more prone to juvenile DM. Gender is a factor in dogs with females being 3 times more likely to develop DM than males.  Most cats are over 8 years of age when diagnosed. Genetics may play a role in some breeds. Neutered males are affected most frequently in addition to obesity being a risk factor.

    Clinical Signs:

    The onset of diabetes is usually very gradual and easily missed by the owner until it is quite advanced. Common clinical signs of DM include an increase in water intake (polydypsia), an increase in urination (polyuria), an increase in food intake (polyphagia), and weight loss although some animals will still be obese upon presentation. Cataract formation is common in dogs with DM, but rare in cats. Cats may have icterus (jaundice) due to concurrent hepatic lipidosis and/or pancreatitis, but icterus is not common in dogs unless they have pancreatitis. Cats may also develop a peripheral neuropathy characterized by plantigrade stance to the pelvic limbs; such neuropathies are rare in dogs. Diabetes mellitus has been associated with immune suppression, retinopathy, hypertension, hypotension, and proteinuria. 


    Normal blood glucose (BG) is 80 - 120 mg/dl. The diagnosis of DM is based on persistent fasting hyperglycemia of usually > 200 mg/dl. If the BG is between 120 - 200 mg/dl, consider stress, post-prandial hyperglycemia, and excess diabetogenic hormones.  Diabetes can be confirmed with the addition of a urinalysis and test for fructosamine levels. 

    Urinalysis should show glucosuria, which occurs when the blood glucose exceeds 180-225 mg/dL. Urine should be routinely evaluated in the diabetic to monitor for urinary tract infection, ketonuria, and glomerular disease. Significant ketonuria in association with systemic illness suggests diabetic ketoacidosis; ketonuria may also occur with anorexia.

    The concentration of fructosamine in serum reflects the average blood sugar concentration over the preceding two to three weeks. As the fructosamine values are not influenced by sudden fluctuations in blood glucose (such as stress in nervous pets or recent food intake), the fructosamine level is a much more reliable indicator in diabetic monitoring than a single glucose determination. The fructosamine assay is based on the ability of ketoamine-linked glucose residues on glycated serum proteins to reduce nitroblue tetrazolium. Other conditions that alter protein metabolic pathways may interfere with the use of fructosamine in diabetic monitoring. In hyperthyroidism, protein turnover is increased; therefore, results of the fructosamine test must be interpreted cautiously in hyperthyroid patients.

    Hemogram results may indicate a stress leukogram and variable increases in WBC’s due to concurrent infection.

    Serum chemistry changes often include elevated liver enzymes (ALT, AST, SAP) secondary to hepatic lipidosis or pancreatitis. Hyperlipidemia and hypercholesterolemia are due to increased lipolysis and decreased lipogenesis. Amylase and lipase may be elevated with concurrent pancreatitis. Electrolytes are often abnormal in the diabetic ketoacidotic patient.


    The goals are to reduce or eliminate the clinical signs of persistent hyperglycemia, avoid insulin-induced hypoglycemia, and prevent or retard the development of cataracts and other diabetic complications.

    For the diabetic dog, the ideal glucose level is between 90 and 200 mg/dl for most of the day with the lowest glucose nadir occurring halfway between the two daily injections of insulin.  A slightly higher glucose level may be acceptable in cats. Stress can elevate blood glucose and the cat is typically more stressed when in the hospital to check glucose levels.

    Treatment for an uncomplicated diabetic:

    In the dog, begin using one of the following intermediate acting (NPH or Lente) insulins at 0.5 U/kg q 12 hours.  In the cat, Lantus at 0.5 mg/kg is the current insulin used.

    NPH (Isophane) Insulins (Humulin N manufactured by Eli Lilly or Novolin N manufactured by Novo Nordisk) are crystalline suspensions of recombinant human insulin with protamine and zinc resulting in intermediate-acting insulin with a slower onset of action and a longer duration of activity than that of regular insulin. Most are available as 100 units/ml (U-100).

    After the first insulin injection, the blood glucose concentrations should be monitored 2 to 3 times within a 4-12 hour period to ensure that hypoglycemia does not occur at the dose used.

    It is important that proper handling of insulin and correct injection techniques are insured.  Inappropriate handling or improper injections can lead to uncontrolled diabetes.

    If hypoglycemia did not develop during the first injection, then give the patient at least one week on this dose before making any adjustments as long as the patient is eating and not showing any signs of hypoglycemia.

    A blood glucose curve should be performed 7–10 days after insulin is started or anytime after the dose is changed. To perform the curve, the pet is brought into the hospital before feeding or insulin is given and an initial glucose sample is taken. Then, the pet is fed its regular food and insulin is given.  Blood samples are then taken at 2-hour intervals for next 12 hours. The disadvantage to this technique is that some dogs won’t eat as they normally would when they are in a clinic environment.

    Thus, an alternative is to feed and give insulin at home in the morning, then bring the animal into the clinic within an hour of the injection and start the curve then. 

    There is a considerable amount of reliable research data showing that diets high in carbohydrates, low in fat, and high in fiber are helpful in regulating diabetic dogs. These types of diets also lowers the average insulin dose, lowers the average blood sugar, lowers the amount of urine being produced, and lowers glycosolated hemoglobins and fructosamine levels. The carbohydrates in these diets are complex carbohydrates. It is important to avoid diets high in simple sugars, which includes any commercial diet semi-moist food, primarily those packaged in foil packets. Diets high in sugar are absorbed very rapidly before the insulin has time to work. The goal in controlling the diabetes with diet is to balance the absorption of sugar with onset of action of the insulin. A high carbohydrate/low fat diet also decreases plasma free fatty acids, increases the number of insulin receptors, increases insulin action at the receptors, and finally, it decreases cholesterol. High fiber diets reduce insulin resistance. The fiber acts to decrease postprandial hyperglycemia, primarily because it delays gastric emptying. A high fiber diet also decreases absorption of glucose and increases insulin action at the receptor.

    The dog needs to be fed the same amount of the same diet at the same times each day. Daily caloric requirements for maintaining ideal body weight should be calculated and fed. Dogs in poor body condition, however, need to be fed more calories. Dogs with recurrent bouts of pancreatitis should avoid high fat diets. Ideally the dog should be fed prior to the insulin injections so that maximal insulin activity is present when maximal post-prandial glucose is being absorbed from the gut. Treats should be avoided during the day. For dogs used to large meals daily, divide the caloric requirements in half and feed in association with the twice daily insulin injection. For dogs used to eating several small meals a day, spread the calculated caloric requirements out over the day similar to what would be done for a cat.

    Cats with type II diabetes should be on a high protein, low carbohydrate diet. Some recent evidence suggests that high protein rather than high fiber diets may be more useful in cats with diabetes. Ongoing studies suggest that such diets (canned kitten diets) result in a decrease in insulin dosage and even remission of the diabetes. This may be due in part to the high protein requirement of cats coupled with the high carbohydrate content of most commercial cat foods.  Unlike dogs, cats can graze throughout the day if that is what they are used to.  The insulin is given the same way as in the dog and at the same frequency, twice daily. 

    Regular dipstick monitoring for urine glucose may help reduce the risk of hypoglycemia because persistent negative results may indicate subclinical hypoglycemia.

    While fructosamine levels provide a useful tool for the evaluation of overall control of diabetes mellitus and long-term glucose regulation, this test is unable to detect short-term or transient abnormalities in blood glucose values. For instance, a patient may have an average blood glucose level within the reference interval over a period of 1-2 weeks preceding the test, but still have transient daily episodes of hypoglycemia and/or hyperglycemia. Serial measurements of blood and/or urine glucose are necessary for the detection of these short-term alterations and are useful in establishing an initial protocol for the feeding and medication of a diabetic patient. Fructosamine levels are more useful for the evaluation of longer-term control, as well as owner compliance with the administration of insulin.

    Special considerations:

    Insulin Overdosage
    Factors that could lead to insulin overdosage include incomplete mixing of insulin suspensions, administration of insulin at irregular intervals, inappetence, excessive exercise, and increased insulin sensitivity associated with the end of diestrus or treatment of concurrent disease such as hyperadrenocorticism.

    Different types of insulin may require different syringes.  Graduations on syringes designed for use with 100 units/ml insulin preparations represent a different volume from graduations on syringes designed for use with 40 units/ml insulin preparations, and this may also lead to dosing errors.

    Insulin Resistance
    Insulin resistance should be suspected if the insulin dosage is > 1.5 U/kg and blood glucose concentration is > 300 mg/dl.  Listed below are concurrent problems that can cause insulin resistance:

    • Hyperadrenocorticism: Either endogenous or exogenous
    • Hypothyroidism and obesity can induce an insulin resistant state
    • Hyperthyroidism 

    • Acromegaly 

    • Severe hyperglycemia
    • Insulin metabolized too quickly 

    • Infection, or concurrent illness 

    • Obesity 

    • Pancreatitis

    • Poor insulin absorption 

    • Antigenic insulin or insulin components 

    • Administration of progestational compounds 

    • Stress

    • Renal disease

    • Hepatic disease
    • Pheochromocytoma
    • Neoplasia

    Diabetes is rarely reversible in dogs, but diabetic cats will sometimes regain the ability to produce their own insulin in the pancreas. Cats that developed diabetes after receiving long term glucocorticoids or hormones are more likely to stop needing insulin after a while compared to cats that developed diabetes without a known cause. 

    Glucometers should be compared to commercial laboratory results.  Human glucometers register lower glucose levels in order to protect the human diabetic from over dosing with insulin. And using whole blood will yield results that are about 10-15% lower than actual reading because mechanical dilution by the RBCs displaces serum. Thus using serum or plasma gives a more accurate reading. The AlphaTrak by Abbott (Veterinary) is accurate for animals and closer to serum readings than most human glucose meters. Some have noted that serum glucose values are higher than those found at outside laboratories on same sample. And you have to make sure you key in the cat or dog code before you test the sample.

    Urine may also be monitored for both glucose and ketone values. Dip sticks are available in most pharmacies which allow the measurement of both glucose and ketone levels in the urine. Insulin dosages generally are not changed based on urine glucose readings, but persistently high urine glucose values may indicate the need for further evaluation of the pet’s condition.

    Urine ketone levels can also be monitored easily at home. Occasionally, ketones will be detected in the urine and this is normal. However, if ketone levels persist for longer than 3 days, an immediate visit to the veterinarian for further evaluation is in order.

    Various methods are available to diagnose and monitor diabetic dogs and cats, but fructosamine is the best method for confirming a diagnosis, assuming the pet also shows clinical signs of diabetes and displays hyperglycemia.

    Fructosamine and blood glucose curves are probably the two most valuable tools for monitoring diabetic dogs and cats. The number one cause of death in diabetic dogs and cats is not the disease itself; rather, it is the owner’s frustration with the disease. This is an extremely important point to remember when treating diabetic animals. Good communication with the pet owner is perhaps the most important component of managing the disease.

    It is recommended that clinicians schedule a 30-minute appointment with the client at the time of discharge before sending the diabetic patient home for the first time. During this appointment, clinicians should thoroughly discuss the care required for the patient. Include the following instructions in that discussion: how to give the animal injections, how to store insulin, what types of food to feed and how often, how to recognize the signs of hypoglycemia, and how to react to this condition. Also, include information on what clinical signs to look for in terms of monitoring water intake and urine production.

    The client should be given written instructions for use as a reference once they are caring for the patient at home. It is essential that the clinician and veterinary staff strive to educate the caregiver and motivate them to get involved in the care of their diabetic pet. The goals of treatment include elimination of the clinical signs of diabetes, prevention or slowing of cataract formation and resulting blindness, prevention of potentially dangerous hypoglycemia, and prevention and/or treatment of concurrent illness.

    Successful management of diabetes is achievable with insulin therapy, attention to diet, and exercise. Owners of a diabetic cat or dog can restore their pet’s quality of life through effective management of diabetes mellitus.

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