Approach to Using Trend Arrows in the FreeStyle Libre Flash Glucose Monitoring Systems in Adults

Abstract

The use of personal continuous glucose monitoring (CGM) has expanded dramatically among individuals with diabetes. CGM systems provide retrospective data, as well as the current glucose value and trend arrow data, which indicate the direction and velocity of changing glucose. In 2017, Aleppo and colleagues developed a simplified approach for adults with diabetes to safely adjust rapid-acting insulin doses using trend arrow information in the Dexcom G5 CGM system. Since then, the FreeStyle Libre and FreeStyle Libre 14-day CGM systems have become available in the United States; however, guidance on using trend arrow data that take the unique features of these systems into consideration is lacking. Specifically, the FreeStyle Libre systems do not have automatic alarms, which impact how the system and trend arrow data are used. The Endocrine Society convened an expert panel to address this gap and develop an approach to adjusting rapid-acting insulin doses for adults using trend arrows in the FreeStyle Libre systems. We based our approach on previous work and expanded upon engagement and scanning recommendations, and we incorporated pre-exercise planning specific to these systems. Our approach provides insulin dose adjustments as discrete insulin units based on an individual's insulin sensitivity and directionality of the trend arrow. We focus on the needs of patients treated with multiple daily injections because these individuals currently make up a greater proportion of individuals on intensive insulin therapy. Our recommendations are intended to provide a safe, practical approach to using trend arrows in the FreeStyle Libre systems.

Keywords: continuous glucose monitoring; diabetes; diabetes technology; flash glucose monitoring; scanning; trend arrows.

Figure 1.

Trend arrows in the FreeStyle Libre systems. The FreeStyle Libre systems present trend arrow data as icons on the reader. Trend arrows indicate rates of glucose change (mg/dL per min) and can be described as the anticipated glucose change. Notably, the flat arrow does not indicate no change in sensor glucose readings. The flat arrow indicates steady glucose values with a change of <1 mg/dL per min. For individuals using the FreeStyle Libre systems, more frequent scanning may be warranted to monitor for hypoglycemia when a flat arrow is present and sensor glucose is near the low end of the target range. In general, anticipated glucose may be less accurate when trying to predict changes over extended periods of time (e.g., beyond 20 to 30 min) due to the many factors that may influence glucose concentrations. Conversion: mg/dL × 0.0555 = mmol/L.

Figure 2.

Insulin dose adjustments for adults using trend arrows in the FreeStyle Libre systems. Our recommended approach to adjusting insulin dose using trend arrow data in the FreeStyle Libre systems assumes that the patient has insulin-requiring diabetes, is using rapid-acting insulin for meals and correction, and is using insulin-to-carbohydrate ratio (ICR) and correction factors (CFs) that have been optimized as much as possible. The approach is based on anticipated glucose change and typical insulin sensitivity ranges in adults. The approach utilizes a simple approach to insulin dose calculation: Total insulin dose = food ± correction ± arrow adjustment. It provides adjustments in terms of insulin units over the range of insulin sensitivities to minimize additional calculations. It is generally recommended to start adjusting conservatively and at mealtime to understand how the recommendations impact individual glucose responses. Adjusting the insulin dose using trend arrows does not replace but, rather, adds to standard calculations using ICR and CFs. Importantly, a single arrow up may require additional corrections due to unknown velocity of glucose increase (e.g., >2 mg/dL). The CF (in mg/dL) indicates glucose lowering per unit of rapid-acting insulin. Conversion: mg/dL × 0.0555 = mmol/L.

Figure 3.

Monitoring and treatment decisions using trend arrows in the FreeStyle Libre systems 2 to 4 h following mealtime bolus. Several variables impact glycemia following mealtime bolus. During the 4 h following mealtime bolus, individuals needing corrective active should rely on current sensor glucose and predetermined CF and ICR values. Importantly, the approach relies on the accurate determination and use of insulin-to-carbohydrate ratio (ICR) and correction factors (CFs) as insulin dose parameters. Individuals should not rely on insulin dose adjustments using trend arrow data during this time. The following is based on the protocol used in the REPLACE-BG study [21] and has been modified to account for the unique features of the FreeStyle Libre system and includes observed trend arrows for the FreeStyle Libre systems. In general, individuals should avoid taking corrective action by bolus insulin dose within the first 2 h after eating. Insulin stacking is a primary concern during this time. Beyond 4 h, it is assumed that most, if not all, carbohydrate has entered the system and that there is no active bolus insulin on board. In this case, the authors recommend using the trend arrows for dose adjustment (Fig. 2). The CF (in mg/dL) indicates glucose lowering per unit of rapid-acting insulin. Conversion: mg/dL × 0.0555 = mmol/L.

Figure 4.

Approach for pre-exercise/activity planning based on current glucose concentration and trend arrow direction. The following recommendations are based on the consensus statement by Riddell et al. [31] and our own clinical experience. Our pre-exercise planning approach takes the unique features of the FreeStyle Libre systems approved in the United States into consideration including the scanning requirement and trend arrow information. In addition to the suggested planning steps, individuals should be aware of how they respond to different types and/or durations of exercise and plan accordingly in advance of activities as best as possible. In general, frequent scanning is recommended for individuals using the FreeStyle Libre systems during exercise.