A Practical Approach to Using Trend Arrows on the Dexcom G5 CGM System for the Management of Adults With Diabetes

Abstract

After reviewing previously published methods, we developed a practical approach to adjusting insulin doses based on insulin sensitivity for adult patients with diabetes using rtCGM trend arrow data.

Keywords: continuous glucose monitoring; diabetes; fine-tuning; insulin dose adjustment; insulin dosing; trend arrows.

Figure 1.

Dexcom G5 trend arrows. Dexcom G5 presents trend arrow data as icons on the Dexcom G5 Receiver and on the Dexcom G5 Mobile and Dexcom Follow apps (App) on compatible smart devices. According to the manufacturer, trend arrows indicate rates of glucose change (mg/dL per minute) and can be described as the anticipated glucose change in 30 minutes. Notably, the FLAT arrow (➡) indicates steady glucose values but does not indicate zero change. Note that trend arrows are determined by recent rtCGM measurements (generally the most recent 10 minutes of glucose values). In general, anticipated glucose may be less accurate when trying to predict changes over extended periods of time (e.g., beyond 20 to 30 minutes) due to the many factors that may influence glucose levels. Conversion: mg/dL × 0.0555 = mmol/L.

Figure 2.

Previous methods to adjust insulin doses using trend arrows. Three previously published methods for adjusting insulin dose using rtCGM trend arrow data are compared [DirecNet (Abbott system) [6], Scheiner (Medtronic and Dexcom systems) [7], and Pettus/Edelman (Dexcom system)] [8]. The DirecNet method takes total insulin dosage including carbohydrate consumption (if any) into consideration. Scheiner and Pettus/Edelman methods are based on anticipated change in blood glucose with the Scheiner method being more conservative in insulin adjustment. Notably, the author of the Scheiner method has presented slightly modified values in recent presentations (personal communication) relative to past publication [7]. We use the more recently presented values in this comparison. All three require calculations beyond correction and carbohydrate consumption. All three assume the patient has insulin requiring diabetes and is using rapid-acting insulin for meals and correction. Note that the recently published Klonoff/Kerr formula recommends adjusting insulin doses by 1, 1.5, or 2 U supplements/decrements for rates of change of 1 to 2, 2 to 3, and >3 mg/dL/min, respectively [9]. Conversion: mg/dL × 0.0555 = mmol/L.

Figure 3.

New approach to adjust insulin doses using trend arrows in adults with diabetes. This figure outlines our approach to adjusting insulin dose using trend arrow data from the Dexcom G5. The approach is based on anticipated glucose change and typical insulin sensitivity ranges in adults. This simplified, practical approach 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 to understand how the recommendations impact individuals. The authors also recommend individuals use the REPLACE-BG study approach to minimize hypo- and hyperglycemia during the 4 hours following a meal (Fig. 4) rather than these insulin dose adjustments. It is essential to understand that adjusting insulin dose using trend arrows does not replace but adds to standard calculations using ICR and CF. The approach assumes the patient has insulin requiring diabetes, is using rapid-acting insulin for meals and correction, and is using ICR and CF factors that have been accurately determined. Conversion: mg/dL × 0.0555 = mmol/L. CF, correction factor in mg/dL indicates glucose lowering per unit of rapid-acting insulin; ICR, insulin to carbohydrate ratio; U, units of rapid-acting insulin.

Figure 4.

Approach to postmeal monitoring and treatment using trend arrows. These suggestions are based on the REPLACE-BG trial [19], which demonstrated that the use of nonadjunctive rtCGM for insulin dose decisions was a safe and effective alternative to conventional adjunctive CGM use. In that setting, instructions were given to participants to monitor trend arrows and minimize glucose extremes following meals. It is especially important to take a standard approach to prevent insulin “stacking” and provide correction at appropriate times following meals. Importantly, these suggestions only use the patient’s CF and do not use the adjustments for trend arrows presented in Fig. 3. It is recommended that no corrective action be taken within the first 2 hours of eating to prevent glucose extremes. Recommendations serve as a guide for postprandial monitoring and correction. Beyond 4 hours, it is assumed that most, if not all, carbohydrate has entered the system and that there is no active insulin on board. In this case, the authors recommend using the trend arrows for dose adjustment (Fig. 3). Conversion: mg/dL × 0.0555 = mmol/L. CGM, continuous glucose monitor.

Figure 5.

Sensitivity comparison of methods to adjust insulin doses using trend arrows in adult patients. The figure is a visual comparison of insulin dose adjustments according to previous methods based on anticipated glucose (Scheiner and Pettus/Edelman) and our suggested approach based on insulin sensitivity ranges (Endocrine Society approach). The illustration shows that our approach aligns well with existing methods that indirectly use insulin sensitivity to adjust insulin doses while overcoming some of the limitations (e.g., a need for additional calculations and minimum increments possible for MDI-treated patients). When applied to lower CF ranges (e.g., <25), our approach is more conservative, whereas in the midrange (e.g., 50 to <75), it is more aggressive. However, one must consider that the conversions used in our approach are based on 30 minutes. When considering the anticipated glucose at 1 hour, our suggested dose adjustments become more conservative. For example, a single UP trend arrow indicates that glucose is rising 2 to 3 mg/dL/min. At 30 minutes, the anticipated glucose would be 60 to 90 mg/dL higher. However, the anticipated glucose could be as much as 120 to 180 mg/dL higher at 60 minutes if exposed to other perturbations. If an individual’s CF was 60, our approach would recommend adding 1.5 U of rapid-acting insulin to the premeal bolus. The additional 1.5 U of insulin would be expected to provide additional glucose lowering of 60 mg/dL over the 60 minutes. Given that the 60-minute anticipated glucose could potentially be much higher at 1-hour, our suggestion could be considered conservative. The expected glucose would be closer to target, postprandially, without overcorrecting and without increasing risk for hypoglycemia. As noted, these recommendations are starting points and should be readjusted as experience increases and responsiveness is observed and understood. Conversion: mg/dL × 0.0555 = mmol/L. CF, correction factor in mg/dL indicates glucose lowering per unit of rapid-acting insulin; U, units of rapid-acting insulin.