Specialty Spotlight: Flash Glucose Monitors – the Cure for the Difficult Diabetic?
Flash Glucose Monitors – the Cure for the Difficult Diabetic?
Sara Arnold, DVM, DACVIM (Internal Medicine)
Difficult diabetics are exhausting. When we see a new consult for a diabetic on our internal medicine service, that appointment almost surely promises to be the longest one of the day. Between the extensive histories, comorbidities, dietary changes, review of insulin administration, storage, etc., the time invested in these patients is extensive. Frustratingly, determining the status of diabetic regulation can also be difficult. Fructosamines are easy and quick but nonspecific, telling you nothing about the glucose nadir or duration of action of the insulin. Blood glucose curves are more specific but either require an adventurous owner and extensive training or a fair amount of staff time in the hospital. Also, glucose curves can vary dramatically on a day to day basis depending on the home environment (who is sneaking Fido treats?), exercise regimen, or stress levels of the pet. For simple diabetics, these aforementioned monitoring techniques are likely more than adequate. However, for a difficult diabetic that is experiencing dramatic fluctuations in glucose, we sadly need more data to best direct therapy.
Flash glucose monitors may be a way to gain this information, but they have their own set of challenges. Currently, the Freestyle Libre monitor by Abbott is the only flash glucose monitor commercially available. Via a disposable application device, these monitors insert a catheter into the subcutaneous space to measure interstitial glucose. The device records a glucose reading every 15 minutes, and the data is stored in the sensor for up to 8 hours. Periodically, the sensor has to be scanned to download these glucose readings and free up memory for continuous recording. The Freestyle Libre sensors are one-time use and generally cost around $65 (some savvy owners have found them for < $30) and will provide glucose readings for a maximum of 14 days. They do not require any calibration via a handheld glucometer, but glucose measurements at the extremes of the reading range (> 400mg/dl and < 70mg/dl) should be confirmed manually, particularly in the face of clinical signs. Sadly, since this is a human product, we cannot order them directly, but the sensors are readily available at most human pharmacies. This low cost and the fact that there is no absolute requirement to draw a blood glucose makes this monitoring device much more feasible for many of our owners.
Another huge benefit of the Freestyle Libre system is the availability of free data sharing applications through Abbott. Owners will utilize a program called Librelink (NOT LibreLink up!!), and this will connect to the provider’s account created with the Libreview website. These programs allow owners to upload data from the sensor frequently throughout the 14 day period, and the results can be viewed remotely in a variety of formats. We generally find the glucose graphs most useful (figure 1). This almost instant data sharing allows us to monitor diabetics in real-time and better council owners over the phone if they are having a problem.
Like anything in medicine, however, these monitors are far from perfect, and there are many challenges that we have also encountered:
Placement: Sensors should be placed over a fatty deposit (or at least a larger muscle group) in an area where pets cannot easily lick/chew. This can be difficult in an emaciated or very small patient. It is also important that the device is placed in a low motion area that is not near the insulin administration site. I generally try to place monitors over the dorsolateral fat pads (“love handles”) when present. In emaciated patients, you can try the lateral cervical area (this prevents the pet from wearing a collar!) or epaxial musculature. The lateral thorax can be considered in larger dogs or more obese patients.
Adhesive: It is very common for the monitors to detach long before their 14-day lifespan. In order to facilitate adhesion, close clipping of the fur is recommended. After cleaning the area with alcohol +/- chlorohexidine and allowing the area to fully dry, you can apply a topical adhesive to the skin. Products suggested (but not recommended) by Abbott include Torbot Skin Tac™, SKIN-PREP™ Protective Barrier Wipe, Mastisol® Liquid Adhesive. We have generally used a very, very small amount of Krazy glue (3 x 1mm drops in a triangle arrangement) applied directly to the adhesive pad without contacting the needle. The sensor can later be removed with acetone at home or with a medical adhesive remover in the hospital. Local dermatitis/redness is not uncommon after removal but generally heals on its own with some mild scabbing.
Technical difficulties: For more technologically savvy owners, these monitors are a breeze. However, some owners struggle with the technology, particularly with uploading the data. The sensor can be scanned using an app with certain smartphones or with a reader that can be purchased at the pharmacy (approximate cost of the reader is also around $65, and the reader is also a handheld glucometer). If the owner is scanning with a smartphone, then the data is instantly uploaded to the cloud when they have an available internet connection. If the owner is using a reader, this device must be manually connected to a computer and the data uploaded for us to gain access. Given that the product is not licensed to be sold to veterinary patients, the company is also very reluctant to provide any technical support once they are made aware that we are using the product on a dog/cat.
Data review: Reviewing the large amount of data that is gathered takes substantial time. We will frequently contact owners multiples times per week to discuss the patient’s status or adjust insulin/feeding recommendations based on glucose trends. It is also easy to quickly become reliant on this constant data feed and feel as though we should always have a glucose monitor on the pet. It is important to remember that too frequently adjusting insulin or feeding recommendations can result in more erratic glucose patterns. Slow and steady adjustment remains the recommendation.
Overall, these glucose monitors have now become routine practice for many of our challenging diabetic cases at UVS. Please note, there are a handful of small clinical studies documenting the efficacy of these monitors in dogs, but nothing has yet to be published with their use in cats (we are using them in cats with fairly good results). Also, as Abbott states on their website, the accuracy of these monitors declines significantly at very low and very high glucose readings. Studies suggest that 50% of low glucose readings are falsely low, and 22% of low glucose readings can be missed. In general, we counsel owners that the absolute glucose numbers are not always accurate, but in general, the trends in the glucose levels are reliable. We still need to pay attention to clinical signs, and any patient who has clinical signs of hypoglycemia should have their blood glucose evaluated even if the monitor reports a normal glucose level. We have not yet started to employ these monitors with hospitalized ketotic patients, but there is some limited data to suggest that these patients may benefit from flash glucose monitors and may be a way to avoid placement of central lines. Please also note that a Freestyle Libre 2 system was recently released, and this is a CONTINUOUS glucose monitor. Continuous glucose monitors are generally more expensive, with more frequent alarms/notifications for owners to manage. We currently do not have any experience with the Freestyle Libre 2. There is a wealth of more detailed information on the Freestyle Libre present on their website and also on VIN, but we are also always happy to help if you have any questions or concerns as you start to employ these monitors in your practice.
Happy glucose monitoring!
-Sara Arnold, DVM, DACVIM
Figure 1: This is a sample graph provided by the Libreview website on one of our patients. The owner can make notes regarding meal times (apple symbol), insulin dose, and other mishaps (exercise, a complication with dose administration). The ideal glucose ranges (gray shaded area) can be adjusted, but we recommend using the maximum range (250mg/dl – 70mg/dl). The maximum recorded glucose is 350mg/dl, but the maximum number you can reach when scanned is 500mg/dl. The lowest recorded value with scanning is 20mg/dl.
- Corradini S, Pilosio B, Dondi F, et al. Accuracy of a Flash Glucose Monitoring System in
- Diabetic Dogs. J Vet Intern Med. 2016;30(4):983-988. doi:10.1111/jvim.14355
- Fleeman L, Flash Glucose Monitoring of Diabetic Dogs and Cats, ACVIM Forum 2019
- Freestyle Libre website – www.Freestylelibre.us
- Malerba E, Cattani C, Del Baldo F, et al. Accuracy of a flash glucose monitoring system in dogs with diabetic ketoacidosis. J Vet Intern Med. 2020;34(1):83-91. doi:10.1111/jvim.15657
- Silva DD, Cecci GRM, Biz G, Chiaro FN, Zanutto MS. Evaluation of a flash glucose monitoring system in dogs with diabetic ketoacidosis [published online ahead of print, 2020 Jul 18]. Domest Anim Endocrinol. 2020;74:106525. doi:10.1016/j.domaniend.2020.106525
- Wilson S, VIN Article, FreeStyle Libre Glucose Monitor FAQ, March 7, 2019