Nearly all diabetic dogs and over 50% of diabetic cats rely on insulin given by their owners.

Diabetes mellitus is a fairly common cause of polyuria/polydipsia in cats and dogs. In nearly all diabetic dogs and over 50% of diabetic are dependent on insulin given by owners. In the other 30-50% of cats, the disease can be treated with diet, exercise, and oral medications. Either way, it remains a difficult disease to manage.

What causes it? Diabetes Mellitus (DM) results from a drop in the insulin levels in the body (or, in some cases, the body’s perception that insulin levels have dropped). Insulin is produced by the pancreas and, among other things, acts on the liver, muscles, and fat deposits to cause them to take glucose out of the blood and store it as glycogen or fat. If the ß cells in the pancreas stop making insulin – or receptors in tissues stop recognizing it – the glucose stays at high levels in the blood, can spill into the urine, and can create a multitude of health concerns that we associate with DM, including cataracts, glaucoma, urinary tract infections, weakness in hind legs, and life-threatening ketoacidosis.

How does DM cause PU/PD? The increased glucose in the blood overwhelms the kidneys, which can no longer filter out all the glucose, and some spills into the urine. The glucose in the urine draws water in from the body, causing an increased volume of urine (polyuria). To avoid becoming dehydrated, the pet consumes more water (polydipsia).

Clinical signs: The first three things the observant owner will notice are polyuria, polydipsia, and an increase in appetite (often in combination with weight loss). DM often occurs in older, overweight pets, so the weight loss is sometimes seen as a good thing. But PU/PD is rarely met with happiness. Other clinical signs might include hind limb weakness, lack of grooming, dry hair coat, and decreased ability to jump.

Diagnosis: In addition to the clinical signs listed above, diagnosis depends on lab work. The pet must have persistent (repeated) elevated blood glucose levels, as well as glucose in the urine. One reason for these specific guidelines is that non-diabetic cats will occasionally have elevated blood glucose levels during a vet visit as a result of stress; and some animals with kidney problems can have glucose in their urine but have normal levels in their blood. Only those animals with DM will have consistently elevated blood glucose and glucose in the urine. Other problems on the lab work in diabetic animals often include elevated cholesterol and fats, elevated liver enzymes, bacteria and protein in the urine, and variable ketones in the urine.

Treatment: The overall goal of DM treatment is to lower circulating blood glucose to a range the body can handle. The treatment plan is typically threefold: correct the insulin deficiency by giving insulin, change the diet and feeding schedule to minimize post-meal hyperglycemia, and manage weight and concurrent diseases to improve insulin sensitivity in the tissues. In our pets, we do not aim to keep the glucose levels in the “normal” range, because this would require a level of monitoring that the typical owner would find onerous. As it turns out, rigid control is not necessary, because our pets do not often live long enough to develop many of the long-term effects seen in human diabetics.

Treatment Monitoring: Monitoring of DM treatment is critical, as the pet’s insulin requirements can change over time. At home, the owner can watch the pet for activity level, frequency/volume of drinking and urination, ability to jump (mainly cats), stability of body weight, and perhaps blood glucose levels via a personal glucometer.

At the vet clinic, a newly-diagnosed pet will require frequent blood tests to find the right starting level of insulin. After a good level has been attained, monitoring may happen via periodic “blood glucose curves,” which are glucose readings taken at specific intervals over the course of a day, or via a “fructosamine level,” which is a single blood test that measures the average glucose level over the previous several weeks. Different veterinarians prefer different monitoring methods.

In a few cats, diabetes has unexpectedly been reversed – that is to say that, after several elevated glucose levels in blood and urine, test results were suddenly normal. This is by no means the norm. In the overwhelming majority of cases, DM requires a lifetime of treatment.

DM in Crisis – Diabetic Ketoacidosis: Sometimes an owner may miss the warning signs of DM – or an insulin dependent pet may develop concurrent pancreatitis or other infection – and the pet develops diabetic ketoacidosis (DKA). In DKA, the liver shifts from its normal function of storing fats and begins turning free fatty acids into ketone bodies (an appropriate survival mechanism during starvation, but quite inappropriate in a well-fed pet). These ketone bodies cause the blood to become more acidic than the body can comfortably handle. The ketones in the blood draw water out of the cells of the body, causing cellular dehydration and dysfunction. Then, they overwhelm the kidneys and spill into the urine, drawing water and electrolytes with them and dehydrating the whole animal. The DKA pet typically begins vomiting, becomes lethargic, and stops eating. This is a life-threatening situation that requires immediate veterinary care.

If you have reason to suspect your pet might be diabetic, you’ll want to see your vet as soon as possible. Initial lab work can rule out diabetes (and maybe give you a clue what’s really going on with your pet). Repeated lab work can confirm the diagnosis of DM. While that diagnosis is not a happy thing, delaying treatment can be life threatening.