The Influence of Skin Thickness on Flash Glucose Monitoring System Accuracy in Dogs with Diabetes Mellitus

A concept for human use of real-time and remote monitoring of diabetic subjects using intermittent scanned continuous glucose measurement

BACKGROUND

Flash glucose monitoring systems like the FreeStyle Libre (FSL) sensor have gained popularity for monitoring glucose levels in people with diabetes mellitus. This sensor can be paired with an off-label converted real-time continuous glucose monitor (c-rtCGM) plus an ad hoc computer/smartphone interface for remote real-time monitoring of diabetic subjects, allowing for trend analysis and alarm generation.

OBJECTIVES

This work evaluates the accuracy and agreement between the FSL sensor and the developed c-rtCGM system. As real-time monitoring is the main feature, the system's connectivity was assessed at 5-min intervals during the trials.

METHODS

One week of glucose data were collected from 16 type 1 diabetic rats using the FSL sensor and the c-rtCGM. Baseline blood samples were taken the first day before inducing type 1 diabetes with streptozotocin. Once confirmed diabetic rats, FSL and c-rtCGM, were implanted, and to improve data matching between the two monitoring devices, the c-rtCGM was calibrated to the FSL glucometer readings. A factorial design 2 × 3^3 and a second-order regression was used to find the base values of the linear model transformation of the raw data obtained from the sensor. Accuracy, agreement, and connectivity were assessed by median absolute relative difference (Median ARD), range averaging times, Parkes consensus error grid analysis (EGA), and Bland-Altman analysis with a non-parametric approach.

RESULTS

Compared to the FSL sensor, the c-rtCGM had an overall Median ARD of 6.58%, with 93.06% of results in zone A when calibration was not carried out. When calibration frequency changed from every 50 h to 1 h, the overall Median ARD improved from 6.68% to 2.41%, respectively. The connectivity evaluation showed that 95% of data was successfully received every 5 min by the computer interface.

CONCLUSIONS AND CLINICAL IMPORTANCE

The results demonstrate the feasibility and reliability of real-time and remote subjects with diabetes monitoring using the developed c-rtCGM system. Performing calibrations relative to the FSL readings increases the accuracy of the data displayed at the interface.

Complications associated with a flash glucose monitoring system in diabetic dogs

Interstitial glucose monitoring systems are commonly being used in diabetic dogs. The aim of this study was to document the incidence of complications associated with the use of a flash glucose monitoring system (FGMS) in dogs. Medical records of dogs that had placement of a 14-day FGMS during a 1-year period were reviewed. Data retrieved included the number of days the sensor remained attached and functional, sensor detachment, sensor failure prior to the end of the 14-day monitoring period, and dermatologic changes at the sensor site. Descriptive statistics were used to characterize the data. Thirty-four dogs had FGMSs placed. Most [32/34 (94%)] sensors were placed over the dorsolateral aspect of the thorax caudal to the scapula. Twenty-four sensors (71%) remained attached for the full 14 days. Incidence of complications associated with FGMS use was 13/34 (38%). The most frequent complication was mild dermatologic changes at the sensor site [6/34 (18%)]. Erythema and crusting at the attachment site were common and could be related to contact dermatitis, hypersensitivity, or skin preparation prior to placement. Flash glucose monitoring systems are safe in dogs, although there are some potential complications that should be discussed with dog owners.

Assessment of the FreeStyle Libre 2 interstitial glucose monitor in hypo- and euglycemic cats

BACKGROUND

Continuous glucose monitoring systems have been validated for eu- and hyperglycemic cats. The FreeStyle Libre 2 (FSL2) is sufficiently accurate in people during hypoglycemia to guide critical treatment decisions without confirmation of blood glucose concentration (BG).

OBJECTIVES

Assess FSL2 accuracy in cats with hypoglycemia.

ANIMALS

Nine healthy, purpose-bred cats.

METHODS

Hyperinsulinemic-hypoglycemic clamps were performed by IV infusion of regular insulin (constant rate) and glucose (variable rate). Interstitial glucose concentration (IG), measured by FSL2, was compared to BG measured by AlphaTrak2. Data were analyzed for all paired measurements (n = 364) and separately during stable BG (≤1 mg/dL/min change over 10 minutes). Pearson's r test, Bland-Altman test, and Parkes Error Grid analysis respectively were used to determine correlation, bias, and clinical accuracy (P < .05 considered significant).

RESULTS

Overall, BG and IG correlated strongly (r = 0.83, P < .0001) in stable glycemia and moderately at all rates of change (r = 0.69, P < .0001). Interstitial glucose concentration underestimated BG in euglycemia, but the BG-IG difference was progressively smaller as BG decreased (12.9 ± 12.2, 8.8 ± 11.2, -3.2 ± 7.4, and -7.8 ± 5.2 mg/dL in the ranges of 80-120 [n = 64], 60-79 [n = 29], 50-59 [n = 71], and 29-49 mg/dL [n = 53], respectively).

CONCLUSIONS

Although IG underestimates BG throughout most of the hypo-euglycemic range, IG generally overestimates BG in marked hypoglycemia (<60 mg/dL). It is therefore imperative to evaluate FSL2 results in this critical range with caution.

Continuous Glucose Monitoring in Dogs and Cats: Application of New Technology to an Old Problem

In recent years, glucose monitoring has been revolutionized by the development of continuous glucose monitoring systems (CGMS), which are wearable non/minimally invasive devices that measure glucose concentration almost continuously for several consecutive d/wk. The Abbott FreeStyle Libre is the CGMS used most commonly. It has adequate clinical accuracy both in dogs and cats, even though the accuracy is lower in the hypoglycemic range. It allows an accurate identification of glycemic excursions occurring throughout the day as well as of glucose variations during consecutive days, enabling the clinician to make a more informed decision about the insulin dose and frequency of administration.

Clinical utility of serum fructosamine in long-term monitoring of diabetes mellitus in dogs

BACKGROUND

Serum fructosamine (sFA) is used to assess glycaemic control in dogs with diabetes mellitus (DM). Nevertheless, its interpretation is hindered by several limitations.

METHODS

This retrospective study evaluates the long-term diagnostic performance of sFA for monitoring clinical control of DM. sFA, bodyweight, appetite, presence of polyuria/polydipsia and clinical scores (CS; well-controlled DM, CS-0; uncontrolled DM, CS-1) were recorded.

RESULTS

The study included 75 dogs (321 visits; median 3 visits/dog; range 1-19). Mean sFA was higher (p < 0.001) on visits with CS-1 (584 μmol/L; 95% confidence interval [95% CI] 561-608) than on visits with CS-0 (506 μmol/L; 95% CI 484-528). Increases in sFA increased   the odds ratio for CS-1 (1.37; 95% CI 1.24-1.52, p < 0.001). sFA was moderately predictive of the CS (area under receiver operating characteristic curve = 0.75; 95% CI 0.70-0.80; p < 0.0001), with a 486 μmol/L cutoff yielding 80% sensitivity and 59% specificity. Mean sFA was lower (p = 0.005) when hypoglycaemic episodes were suspected (496 μmol/L; 95% CI 450-541) than in their absence (572 μmol/L; 95% CI 548-596). sFA is moderately accurate for classifying CS in diabetic dogs. Decreasing sFA over follow-ups indicates improved CS but might suggest occurrence of hypoglycaemic episodes.

LIMITATIONS

Retrospective design, variable treatments and comorbidities are limitations of this study.

CONCLUSION

sFA has a moderate clinical utility in the long-term monitoring of diabetic dogs, but may serve as a first-line, accessible diagnostic tool. Discordant CS and sFA evaluation, or decreased sFA, warrants additional monitoring (i.e., continuous glucose monitoring).

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.