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TRADITIONAL DIABETIC MONITORING GOALS AND STRATEGIES

The primary management goals for the diabetic canine or feline patient include improving clinical signs (i.e., polyuria, polydipsia, and polyphagia), maintaining body weight, and avoiding clinical hypoglycemia or diabetic ketoacidosis. Traditional options for assessing glycemic control include evaluation of body weight, clinical signs, and either serum fructosamine concentration or blood glucose curves. Hemoglobin A1C is commonly used in human medicine, but not widely available for veterinary patients and is not discussed in detail. The veterinarian’s goals are to understand the animal’s response to insulin and dietary therapy, determine the duration of insulin response, and assess the risk of hypoglycemia. Both serum fructosamine and blood glucose curves have limitations.

Serum fructosamine measures glycosylated albumin and reflects average glucose over the past several weeks. It cannot identify episodic hypoglycemia. Serum fructosamine can be normal with early-onset or mild diabetes mellitus, and can be influenced by non-diabetic states (e.g. hypothyroidism can falsely increase, hypoalbuminemia can falsely decrease). Sometimes, serum fructosamine will be discordant with clinical signs. For example, an animal might not display any clinical signs consistent with diabetes mellitus yet have a serum fructosamine consistent with poor glycemic control, which can be confusing and frustrating for clinicians. Used alone, serum fructosamine is an imperfect surrogate marker to classify glycemic control.1 When compared to continuous interstitial glucose monitoring1 or clinical assessment tools2, serum fructosamine was not reliable to differentiate dogs with good, moderate, or poor control and there is a lot of overlap between groups.

Blood glucose curves can have large day-to-day fluctuations and are can be affected by stress hyperglycemia. Certain types of insulin (i.e. insulin suspensions), as well as environmental influences, result in wide glycemic variability. Additionally, periods of hypoglycemia can be easily missed, especially if occurring at night. It can be difficult for some owners to maintain compliance with repeated glucose curves.

CONTINUOUS INTERSTITIAL GLUCOSE MONITORING (CIGM)

Recently, a new device category was introduced to the market, the flash glucose monitoring system (Freestyle Libre, Abbott Diabetes Care), which measures glucose in the interstitial space through enzymatic (glucose oxidase) and amperometric (electrodes) systems. Briefly, reduction of glucose by glucose oxidase results in generation of an electric current, the intensity of which is proportional to the interstitial glucose concentration.3 It is important to recognize that the interstitial glucose is not exactly the same as the blood glucose (hence, the readings will be different if blood glucose is measured with a handheld glucometer), but the blood glucose and interstitial glucose have been shown to equilibrate after approximately 5 to 11 minutes in cats4 and dogs5, respectively. The detection limits of the sensor (for the display) are between 40 mg/dL and 400 mg/ dL, although the sensor can read between 20 and 500 mg/dL; the sensor is less accurate at extreme values. The system is factorycalibrated so blood calibration is not required. Several studies have demonstrated accuracy and clinical utility in veterinary medicine.3-5

The sensor has a round shape and a flexible filament (5 mm long) that is introduced into the subcutaneous space transcutaneously using a manufacturer-supplied applicator. The sensor is for onetime use and can last up to 14 days (15 days for Libre3 Plus).

Smart phones (both Android and iPhone) have largely replaced handheld readers. The sensor will provide the first reading 60 minutes after application. The sensor will measure the interstitial glucose every minute and the readings are stored every 15 minutes. With the Libre3 and Libre3Plus, data automatically is sent via Bluetooth from the sensor to the smartphone app. Using the free, cloud-based Abbott software you can link patients to your hospital account. To link patients, you can either send them an email invitation to join your account or provide them your account practice ID number.

  • Libre3 phone app- ONE owner signs into account (If more than one phone is used to sign into account, then no data is visible)
  • LibreLink phone app- can share data with up to 20 users
  • LibreView- online platform that makes reports & connects your hospital account to patients

The online software generates summary glucose reports, daily mean glucose, as well as daily logs. Note, the software will delete inactive patients after six months so I usually download the final reports to save in the medical record.

USES FOR CIGM

CIGM can be very useful for routine assessment of the diabetic patient, especially to ensure there are no significant periods of hypoglycemia.1,3,6 CIGM can be used in-hospital to monitor sick dogs or cats with diabetic ketoacidosis, and can be helpful for that initial at-home period when the animal might not have a normal appetite.7-8 Additionally, CIGM can be used to monitor patients at risk of hypoglycemia, such as pediatrics, and dogs with portosystemic shunt or xylitol toxicity.

2025 COST CONSIDERATIONS

  • 14-day (Libre3) or 15-day (Libre3 Plus) sensor, onetime use, approximately $45-80 owners pick-up from local pharmacy with prescription
  • Free app for iphone and Android
  • Study interpretation fee (charge for your time and expertise)
  • Optional fee for sensor placement (or include in interpretation fee)

BENEFITS OF CIGM

  • Well-tolerated by patients.
  • Patients remain in home environment. There is less stress and, therefore, more reliable readings.
  • Easy to assess day-to-day variation in mean and average glucose, range, nadir, and duration of insulin action.
  • Readily detects hypoglycemia. (Dogs can be either hyperglycemic or hypoglycemic at night. Approximately 50% of dogs will have higher nocturnal glucose concentrations. There can be individual variation in circadian glucose fluctuation, which can be influenced by illness, diet, type and timing of insulin, and exercise.9)
  • Easy to perform and no calibration required.

WHERE TO PLACE SENSORS?

The dorsal neck is a commonly chosen site because there is minimal movement and it is easy to secure the sensor with a light bandage, if desired.10 Between the shoulders on the dorsum is another option, but probably best for obese patients. In one study, the dorsolateral thorax best correlated with blood glucose in dogs but due to the increased movement, sensors at this site had the shortest functional duration.11

COMMON COMPLICATIONS

The most common complication is early sensor detachment, which can occur in up to 30% to 44% of dogs and cats.6-7 This can be due to patient factors, such as scratching, rubbing, high activity, or housemates, or because of ineffective placement or a dysfunctional sensor (i.e. not shaved or cleaned well, movement during placement).

TIPS TO MINIMIZE EARLY SENSOR DETACHMENT:

  • Select location with minimal motion
  • Ensure skin is dry prior to placement
  • Consider tissue glue to the skin-facing surface of the sensor
  • Properly restrain animal for placement
  • Consider light bandage or T-shirt
  • Set up appropriate owner expectations

Another common complication is mild to moderate dermatologic change in approximately 50% of patients, usually cutaneous erythema.1,3,6,8,12 This is a common reaction in humans as well. The exact cause is unknown, but it is thought to be a reaction to the device adhesive or related to traumatic removal. Most of the time, the erythema is transient and self-limiting, but occasionally can be severe (e.g. erosions, ulcers, abscess, severe pruritus).12 Consider the use of a skin barrier film or cream prior to sensor placement. Rarely reported complications include local bleeding, thrombus formation, and pneumothorax. Be sure to remove the sensors when they stop working.

OWNER PERCEPTIONS

In a survey of 50 diabetic pet owners, 94% said they would recommend, 70% said it did not negatively affect their quality of life and 84% would continue to use in the future. It is important to note that some owners were stressed with 12% reporting increased anxiety. Additionally, approximately 1/3 reported that the cost would be difficult to afford long-term.13

References

  1. Zeugswetter FK, Beer R, Schwendenwein I. Evaluation of fructosamine concentration as an index marker for glycaemic control in diabetic dogs. Vet Record 2021. E244. https://doi.org/10.1002/vetr.244
  2. Del Baldo F, Fracassi F. Continuous glucose monitoring in dogs and cats: Application of new technology to an old problem. Vet Clin Small Anim 2023;53:591-613.
  3. DelBaldo F, Canton C, Testa S, et al. Comparison between a flash glucose monitoring system and a portable glucose meter for monitoring dogs with diabetes mellitus. J Vet Intern Med. 2020. http://doi.org/10.1111/jvim.15930
  4. DelBaldo F, Fracassi F, Pires J, et al. Accuracy of a flash glucose monitoring system in cats and determination of the time lag between blood glucose and interstitial glucose concentrations. J Vet Intern Med. 2021; 35(3): 1279-1287. http://doi: 10.1111/jvim.16122.
  5. Wiedmeyer CE, DeClue AE. Continuous glucose monitoring in dogs and cats. J Vet Intern Med. 2008; 22: 2-8.
  6. Corradini S, Pilosio B, Dondi F, et al. Accuracy of a flash glucose monitoring system in diabetic dogs. J Vet Intern Med. 2016; 30:983-988.
  7. Silva DD, Cecci GM, Biz G. Evaluation of a flash glucose monitoring system in dogs with diabetic ketoacidosis. Dom Anim Endocrinol. 2021;74. https://doi.org/10.1016/j.domaniend.2020.106525.
  8. 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 2018. http:// doi.org/10.1111/jvim.15657.
  9. Shea EK, Hess RS. Assessment of postprandial hyperglycemia and circadian fluctuation of glucose concentrations in diabetic dogs using a flash glucose monitoring system. J Vet Intern Med. http://doi.org/10.1111/jvim.16046.
  10. Hafner M, Lutz TA, Reusch CE, et al. Evaluation of sensor sites for continuous glucose monitoring in cats with diabetes mellitus. J Fel Med Surg, 2012; 15(2):117-123. http://doi.org/10.1177/1098612X12463925
  11. Koenig A, Hoenig ME, Jimenez DA. Effect of sensor location in dogs on performance of an interstitial glucose monitor. Am J Vet Res. 2016;77:805-817.
  12. Shoelson AM, Mahony OM, Pavlick M. Complications associated with a flash glucose monitoring system in diabetic cats. J Fel Med Surg. 2020:1-6; http://doi.org/10.1177/1098612X20965012.
  13. Re M, Del Baldo F, Tardo AM, et al. Monitoring of diabetes mellitus using the flash glucose monitoring system: the owners’ point of view. Vet Sci 2023;10(3): doi: 10.3390/vetsci10030203.

About the Author

Shelly Olin | DVM, DACVIM

Dr. Shelly Olin is a native of Charleston, SC. After receiving her DVM from the University of Georgia, she worked as an emergency doctor in Atlanta, GA for two years before pursuing advanced training. After completing an internal medicine residency and becoming a diplomate of ACVIM, she remained as clinical faculty at the University of Tennessee College of Veterinary Medicine. Professional interests include endocrinology, urinary tract disease, minimally-invasive procedures, endoscopy and education.

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