The flash glucose monitoring system (also called continuous glucose monitoring or CGM) is a faster, easier, and less painful way for you to monitor your diabetic pet’s glucose levels at home. There are several flash glucose monitoring systems on the market, of which FreeStyle Libre is one. The following information is only referencing the FreeStyle Libre, as that is the only system with which veterinarians have experience to date, and the only system with published studies in dogs and cats. Unfortunately, the company (Abbott) does not provide support for veterinary use (since it is not specifically approved for use in animals they do not answer questions about animal use on their support line nor do they replace the Sensor should it prematurely detach from an animal or fail to work on an animal).

A flash monitoring system allows you to monitor your pet’s glucose levels at home without pricking foot pads, ears, or lips to collect blood, which means that more frequent readings can be taken without additional stress for you or your pet. Your veterinarian should give you guidelines about when to contact them based on the blood glucose levels.

Flash glucose monitoring systems measure the glucose in the fluid that is present in the tissues under the skin (interstitial fluid glucose). There is a small difference in this measurement as compared to the amount of glucose in the blood, but for the purpose of monitoring your pet’s diabetes, the difference is negligible.

How it Works

A sensor with a tiny, flexible sampling catheter (tube) is implanted in your pet’s skin. The sampling catheter is linked to a glucose analyzer that has a wireless link to a reader similar to a grocery store bar code reader. The reader can sense the glucose level when it is within a few feet of the sensor, but active readings (passing the reader over the sensor) should be taken at intervals recommended by your veterinarian. The sensor should be actively scanned at least every 8 hours to maximize the data capture within that 24-hour period.

Instead of the reader, a smartphone app can be used as the reader if the owner has a compatible smartphone. If you are using a smartphone as the reader and have downloaded both the Libre app and the Libreview app, the data from the reader on the smartphone will automatically transfer every minute to the Libreview site (allowing your health provider to be able to see the data). There is no need to scan the sensor with a smartphone reader; the smartphone needs to be within a certain (unobstructed) distance from the sensor to receive the signal (and Bluetooth needs to be enabled on the phone). An alarm notifies you when a signal loss occurs and the sensor has not communicated with the Libre app for 20 minutes. Signal loss could be caused by the sensor being too far away from your smartphone -- over 6 meters (20 feet) for FreeStyle Libre 2 sensors, over 10 meters (33 ft) for FreeStyle Libre 3 sensors. Additionally, the signal loss alarm can occur if Bluetooth is turned off.

Check the Abbott website or look at the Libre App on the smartphone for compatibility information for the operating system (OS) on your smartphone to be sure you can use your smartphone as the reader. Some smartphones are ‘too updated’ to be able to be used temporarily (after each smartphone operating system update, Abbott checks the new software update for compatibility with its Libre software. There is a lag while that happens). Turn off smartphone updates on your phone while a Libre sensor is on your pet. Abbott is phasing out the older Libre 2 and Libre 3 apps; going forward there will be a single Libre app.

Only one smartphone can be used as the Reader (the phone that is used to start the sensor) but it is possible to transfer using one smartphone as the reader to a different smartphone. Previous data from the currently-used sensor isn’t transferred to the new phone, but that data isn’t lost if you and your health provider are connected via the Libreview.com site.

The Libre 2 sensor is about the size of a quarter and about as thick as two stacked quarters, while the Libre 3 and Libre 3 Plus sensor is 21 mm in diameter and 2.9 mm in height, roughly the size of 2 stacked US pennies.

Sensor with Sampling Catheter

Photo by Dr. Margaret Hammond-Lenzer

How the Sensor is Implanted

Implanting the sensor should be done by your veterinarian. Implanting the sensor takes only seconds and is less painful than a vaccination. Most pets don’t even notice when the sensor is implanted.

A small area on your pet’s back is shaved, the area is cleaned, and the sensor, which comes with its own implantation device, is pressed into the skin. Often, tissue glue is applied to the sensor while it is still in the implantation device, and a liquid adhesive (like SkinTac) is used on the site as well.

Ready for Implantation

Photo by Dr. Margaret Hammond-Lenzer

Sensor Implanted

Photo by Dr. Margaret Hammond-Lenzer

Where do I Get One?

Your veterinarian will write a prescription for the sensor.  Each sensor is used only once and generates 14 days of continuous glucose data (15 days for the Libre 3 and 3 Plus sensors). You will need to purchase a new sensor any time your veterinarian recommends repeating the glucose monitoring .

Since animals have their own ideas, many pets manage to dislodge the sensor before the expiration. Don’t despair, on average, your veterinarian can get several days of data, which can still provide accurate information to manage your dog or cat’s blood glucose concentrations appropriately. Even a day or two of data is no more expensive than a single day-long curve in a veterinary hospital, and the sensor data shows the glucose levels when the pet is not stressed, which is invaluable, especially in cats. 

The independent reader should last for 3 years if you take care of it. A charging cord is supplied in the reader kit, as well as a cable for the reader to connect to a home computer so that you and your veterinarian can both see the data using the Libreview.com site.

How Can I Increase the Odds of Keeping the Sensor On?

Your veterinarian will attempt to find the best area for your pet's sensor placement. A flat area that doesn't move much, isn't within one inch of where the insulin is injected, and that the pet's mouth and back feet can't reach is needed. The ideal area may be different for each pet, especially cats. Some cats leave it more alone if they are wearing a ‘T-shirt’, such as a piece of orthopedic stockinette that has holes cut in it for their legs. You could put an Elizabethan collar on the pet so they can’t turn around and bite it out, then just concentrate on putting it in a place where their back legs don’t easily reach to scratch it off.

How do I Interpret the Information?

Your veterinarian will work with you to make sure you can upload the data from the reader to your computer and send it to the veterinary hospital for review. Because the sensor lasts 14-15 days, your veterinarian can usually change the insulin dose 1-2 times (if necessary) while the sensor is still working and evaluate the results of that change.

This means you and your veterinarian need to figure out how data will be sent to them before the Sensor is activated, so you can take full advantage of the data. By far the easiest way to communicate the data is the Libreview.com site.

Important Information about Hypoglycemia

The flash systems are sometimes not as consistently reliable for pets as they are for humans.

If the flash system indicates that your pet’s glucose level is low and your pet isn’t having signs of low blood glucose (trembling, weakness, panting, seizures, collapse etc.), you should check your pet’s blood glucose with a standard veterinary glucometer before offering any snacks to counteract the hypoglycemia.

If your pet is having signs of hypoglycemia and the flash system is registering a normal glucose level, you should also double-check the flash system against a standard glucometer (and in the meantime, offer food/snacks to counteract any hypoglycemia).

Flash glucose monitoring systems are a big step forward in managing diabetes in our pets. With these systems, your veterinarian has vital information that can help them craft a treatment protocol that exactly fits your pet’s metabolic needs.