Continuous Glucose Monitoring: New Advances in Diabetes Care
By MEGAN TREMELLING, DVM, LVS
The practice of medicine is always evolving. Like other forms of science, it follows a meandering path, sometimes getting lost in false trails and dead ends but always working toward better understanding, better accuracy, better tools and better outcomes. It can be frustrating for researchers to struggle for years to understand a thing or to find out that something we thought we understood was actually wrong, but the trend is always positive eventually. Nowhere is this more clear than in the state of care for type 1 (insulin-dependent) diabetes mellitus, which occurs in dogs as well as in humans.
Diabetes has been known to physicians since ancient times, but it was not until the 1700s that scientists began to understand how the disorder worked, and it was not until the 1920s that insulin was named, isolated and purified to a degree that it could be used to treat diabetes effectively.
Dogs have long been part of diabetes research. The Canadian researchers who first developed the use of insulin worked with dogs before attempting the treatment on humans. Unfortunately, dogs’ early role was exclusively as research subject. In the days before animal welfare regulations were enacted, dogs could and did suffer terribly for the sake of knowledge. The silver lining to this grim cloud is that as companion animal medicine became more established, the knowledge gained could be applied to pets as well as to their owners. By the 1940s, veterinary journals were reporting on the diagnosis and treatment of naturally occurring diabetes in dogs. As the care for humans with diabetes has improved, so too the care for pets with diabetes has improved.
For the management of human diabetes, several types of insulin are made, varying mostly in how quickly they are absorbed and how long they last. This allows veterinarians some options in the choice of insulin therapy for dogs.
Another important development in diabetes care has been an improved ability to measure glucose levels in the urine and, later, in blood. Now, instead of choosing insulin doses on the basis of clinical signs, doctors can calculate appropriate doses of insulin that are customized to their patients. For many years, humans with diabetes have used home blood glucose monitors, obtaining small samples of blood from their fingertips with lancet devices designed for the purpose. It is an unpleasant but very beneficial part of diabetes management, and all humans with diabetes who have access to modern medical care are taught to do it. Unfortunately, home monitoring of blood glucose in pets has not become universal.
The obstacles to home monitoring of blood glucose in dogs are several. In the first place, obviously, dogs don’t have fingertips. It is possible for an owner to obtain blood samples at home, using the lancet devices on their dogs’ ears or pads, though some dogs tolerate this procedure better than others. The second challenge, and perhaps more important, is that it can be challenging for veterinarians to teach owners how to correctly interpret the data they obtain. Humans with diabetes get immediate feedback in the form of their physical condition. Low blood glucose and high blood glucose both cause symptoms that often can be recognized and treated before they become too severe. While we think it likely that dogs can feel their lows and highs in a similar fashion, they can’t tell us about it. This means that attempting to keep their blood glucose under very tight control can backfire and cause more serious problems. I know veterinarians who refuse to have their clients check blood glucoses at home because too many clients in the past have misinterpreted the data and caused inadvertent harm to their pets.
How then do veterinarians manage pets with diabetes? We rely on clinical signs and some in-hospital testing. A test called a glucose curve requires the pet to spend the day at the veterinarian’s office having blood drawn frequently for glucose testing; then the veterinarian assesses the information and makes recommendations on how to dose insulin. This test has some serious limitations. A glucose curve paints a picture of one day only, while dogs, like humans, vary day to day, so the glucose curve may give too small a picture. We also use a blood test called fructosamine (similar to the A1C test used in humans) that gives one number to reflect average blood glucose over several weeks, but that may be too big a picture; it doesn’t give details about what time the glucose decreases, how long it stays down or when it goes up.
Enter the newest development in canine diabetes management: continuous glucose monitoring.
Continuous glucose monitors (CGM) have been used for humans for years. They consist of a tiny sensor that is implanted under the skin along with the accompanying equipment to record the information obtained. Glucose readings can be obtained about every five minutes. Many humans with diabetes wear a CGM every day, using the constant stream of glucose readings to guide their insulin therapy. In some cases, the CGM can be paired with an insulin pump so that the human doesn’t even have to intervene to treat highs and lows; it is done automatically.
Recently, veterinarians have begun to adopt the use of CGM for their patients. There were some bugs to work out since some of the systems designed for human use did not work well on veterinary patients, but improvement has been made, and there are now CGMs that are proven to be accurate in dogs, small enough to be used on even tiny dogs, and affordable for owners. There is no need for a dog to wear a CGM all the time. Rather, veterinarians place a CGM on a patient and leave it for a few days to a week, collecting data as the dog goes about its usual routine at home. Then the veterinarian can use all this information to make better recommendations about insulin use.
CGM is blazing new trails in the care of pets with diabetes. We can hardly wait to see what the next technical breakthrough brings us!