Keynote Message

• Various continuous glucose monitoring systems have been validated for use in dogs and cats. All currently available systems are similarly accurate and differ mostly in cost and convenience. Importantly, CGM units measure interstitial glucose (IG), not blood glucose (BG). Therefore, they report results that often differ from BG concentrations that are measured at the same time. The difference is not only in absolute values but also in timing. There is a delay of a few minutes (at least) between changes in blood glucose and changes in interstitial glucose. Depending on the rate, the direction, and the ambient glucose concentrations, changes in BG are not always fully reflected by changes in IG. Therefore, comparing CGM absolute values to blood glucose concentrations might not be relevant.
• When blood glucose is changing rapidly, there is poor correlation between IG and BG.
• A factory-calibrated flash glucose monitoring system (FGMS, FreeStyle Libre, Abbott) is user-friendly, inexpensive, and seemingly painless upon application. This unit is now routinely used for monitoring of diabetes mellitus in dogs and cats.
• In non-ketotic diabetic dogs, across all glycaemic ranges, the Libre FGMS showed good correlation to BG (rho=0.94). The mean ± SD difference from the reference method was 0.13±2.6 mmol/L (2.3±46.8 mg/dL). However, the accuracy in the hypoglycaemic range was not as extensively studied and showed only a moderate correlation (rho=0.43) with BG underestimated by IG in 69% of samples.
• Lower, but still good correlation was found between BG and IG measured by FGMS in ketotic dogs (r=0.91), however, the potential effect of dehydration and hypoperfusion on this correlation was not evaluated.
• In euglycemic and hyperglycaemic cats, when blood glucose is not changing rapidly, the FreeStyle Libre demonstrates an excellent correlation to BG (r=0.97 [95% CI=0.96–0.98]) with a consistent bias (across the BG range) towards underestimating BG by the FGM (mean ± SD bias 1.3±1.0 mmol/L [23.3±18.1 mg/ml]).
• Clinical experience with insulin pumps is limited in veterinary medicine. New systems that are small and do not have any external tubing are available (e.g., OmniPod®) and seem to work well in dogs. While expensive, insulin pumps allow for better control of BG without the need for repeated injections.

Key References

1.  Ristic JM, Herrtage ME, Walti-Lauger SM, et al. Evaluation of a continuous glucose monitoring system in cats with diabetes mellitus. J Feline Med Surg. 2005;7:153–162. DOI:10.1016/j.jfms.2004.07.006. https://journals.sagepub.com.

2.  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. DOI: 10.1111/jvim.14355. https://onlinelibrary.wiley.com.

3.  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. 2019 Nov 14. DOI: 10.1111/jvim.15657. https://onlinelibrary.wiley.com.