Clinical Evaluation of a Novel CGM-Informed Bolus Calculator with Automatic Glucose Trend Adjustment

Abstract

Background: Expert opinion guidelines and limited data from clinical trials recommend adjustment to bolus insulin doses based on continuous glucose monitor (CGM) trend data, yet minimal evidence exists to support this approach. We performed a clinical evaluation of a novel CGM-informed bolus calculator (CIBC) with automatic insulin bolus dose adjustment based on CGM trend used with sensor-augmented pump therapy. Materials and Methods: In this multicenter, outpatient study, participants 6-70 years of age with type 1 diabetes (T1D) used the Omnipod^® 5 System in Manual Mode, first for 7 days without a connected CGM (standard bolus calculator, SBC, phase 1) and then for 7 days with a connected CGM using the CIBC (CIBC phase 2). The integrated bolus calculator used stored pump settings plus user-estimated meal size and/or either a manually entered capillary glucose value (SBC phase) or an imported current CGM value and trend (CIBC phase) to recommend a bolus amount. The CIBC automatically increased or decreased the suggested bolus amount based on the CGM trend. Results: Twenty-five participants, (mean ± standard deviation) 27 ± 15 years of age, with T1D duration 12 ± 9 years and A1C 7.0% ± 0.9% completed the study. There were significantly fewer sensor readings <70 mg/dL 4 h postbolus with the CIBC compared to the SBC (2.1% ± 2.0% vs. 2.8 ± 2.7, P = 0.03), while percent of sensor readings >180 and 70-180 mg/dL remained the same. There was no difference in insulin use or number of boluses given between the two phases. Conclusion: The CIBC was safe when used with the Omnipod 5 System in Manual Mode, with fewer hypoglycemic readings in the postbolus period compared to the SBC. This trial was registered at ClinicalTrials.gov (NCT04320069).

Keywords: Bolus calculator; Continuous glucose monitoring; Hypoglycemia; Omnipod; Type 1 diabetes.

FIG. 1.

Omnipod 5 application displaying (left) Bolus Calculator screen where users may press the USE CGM button (highlighted with orange box) and (right) Confirm Bolus screen, which calculates the total bolus units needed for the BG value and trend imported from the CGM, as well as any entered carbohydrates. BG, blood glucose; CGM, continuous glucose monitor. Color images are available online.

FIG. 2.

Example calculation with the Omnipod 5 System CGM-informed bolus calculator. In this scenario, the current CGM value is 180 mg/dL with a rising trend, the target BG is 130 mg/dL, the correction factor is 50 mg/dL per unit, and the insulin to carbohydrate ratio is 10 g per unit. There is no IOB. The correction bolus is initially calculated as 1 U. First, the Meal IOB and then the Correction IOB are subtracted from this amount; however, in this example, both IOB amounts are zero so the correction bolus is unchanged at 1 U. The correction bolus is then automatically adjusted from 1 to 1.2 U based on the rising glucose trend. The meal bolus is initially calculated as 3 U. Any remaining Correction IOB is then subtracted; however, in this example, there is no IOB so the meal bolus amount remains at 3 U. The meal bolus is then automatically adjusted from 3 to 3.6 U based on the rising glucose trend. The total bolus is the correction bolus plus the meal bolus (1.2 U plus 3.6 U) for a total of 4.8 U. If using the standard bolus calculator with the same conditions, the total bolus amount would have been determined from the correction and meal bolus amounts before trend adjustment (1 U plus 3 U) for a total of 4 U. Therefore, an additional 0.8 U has been recommended to account for the rising glucose trend. IOB, insulin on board.