Evaluation of the FreeStyle Libre, a flash glucose monitoring system, in client-owned cats with diabetes mellitus

Objectives: Home blood glucose monitoring using a portable blood glucose meter is important in the management of feline diabetes mellitus, but taking blood samples may be stressful for owners and cats. A flash glucose monitoring system measuring interstitial glucose, such as the FreeStyle Libre, overcomes some of these drawbacks. The aim of this study was to evaluate the practical use and analytical and clinical accuracy of the FreeStyle Libre in 41 client-owned diabetic cats. Methods: In this prospective study, interstitial glucose concentrations were measured with the FreeStyle Libre and compared with blood glucose concentrations measured with a portable blood glucose meter (AlphaTRAK) on days 1, 7 or 8 and 14 after application of the device. Cat behaviour during application, location, skin reaction at the attachment site and owner satisfaction were assessed. Accuracy was determined by fulfilment of ISO 15197:2013 criteria, including Bland–Altman plotting and error grid analysis. Results: Placing the device was easy, with 70% of cats showing no reaction. Most sensors were placed on the thoracic wall. Skin reactions at the attachment site were not present or mild in almost all cats. Owners were very satisfied with the use of the FreeStyle Libre. Median functional life of the sensor was 10 days (range 1–14). Good correlation was found between interstitial and blood glucose measurements (rho[r] = 0.88, P <0.0001). Fifty-three percent of interstitial glucose concentrations were within a maximum deviation of 15% from blood glucose concentrations and 92.7% were within the safe risk zones 0 and 1 of the surveillance error grid. Conclusions and relevance: The flash glucose monitoring system was easy to use and owners of diabetic cats were satisfied with its use. Although the device did not completely fulfil ISO requirements, it is sufficiently accurate for glucose monitoring in diabetic cats.