Rate-of-Change Dependence of the Performance of Two CGM Systems During Induced Glucose Swings

Abstract

Introduction: The accuracy of continuous glucose monitoring (CGM) systems is often assessed with respect to blood glucose (BG) readings. CGM readings are affected by a physiological and a technical time delay when compared to BG readings. In this analysis, the dependence of CGM performance parameters on the BG rate of change was investigated for 2 CGM systems. Methods: Data from a previously published study were retrospectively analyzed. An established CGM system (Dexcom G4, Dexcom, San Diego, CA; system A) and a prototype system (Roche Diagnostics GmbH, Mannheim, Germany; system B) with 2 sensors each were worn by 10 subjects in parallel. Glucose swings were induced to achieve rapidly changing BG concentrations. Mean absolute relative differences (MARD) were calculated in different BG rate-of-change categories. In addition, sensor-to-sensor precision was assessed. Results: At BG rates of change of –1 mg/dl/min to 0 mg/dl/min and 0 mg/dl/min to +1 mg/dl/min, MARD results were 12.6% and 11.3% for system A and 8.2% and 10.0% for system B. At rapidly changing BG concentrations (<–3 mg/dl/min and ≥+3 mg/dl/min), higher MARD results were found for both systems, but system B was less affected (system A: 24.9% and 29.6%, system B: 10.6% and 16.3%). The impact of rate of change on sensor-to-sensor precision was less pronounced. Conclusions: Both systems were affected by rapidly changing BG concentrations to some degree, although system B was mostly unaffected by decreasing BG concentrations. It would seem that technological advancements in CGM systems might allow for a more precise tracking of BG concentrations even at rapidly changing BG concentrations.

American Association Of Clinical Endocrinologists And American College Of Endocrinology 2016 Outpatient Glucose Monitoring Consensus Statement

“…Several published studies have compared BGM brands and models by name during headto-head testing (56,57,136,(145)(146)(147)(148). For clinicians and consumers, MARD provides an excellent measure of accuracy and precision when evaluating a BGM (134).…”

Assessing the Accuracy of Continuous Glucose Monitoring (CGM) Calibrated With Capillary Values Using Capillary or Venous Glucose Levels as a Reference

“…Rates of change were calculated based on the capillary glucose readings and was defined as the difference between current and previous (within 20 minutes) glucose sample, given as change in mg/dL/minute. 20 MARD was also estimated in 3 different glucose ranges: hypoglycemia (<4 mmol/L, <72 mg/dL), euglycemia (4-10 mmol/L, 72-180 mg/dL), and hyperglycemia (>10 mmol/L, >180 mg/dL). The various ranges were determined based on venous samples.…”

“…12 Results from this study and previous studies investigating relationships of glucose concentrations in capillary and venous whole blood indicated a significant difference between venous and capillary glucose concentration. 12,[20][21][22] The aim of the present study was to evaluate how the estimated accuracy of CGM differs when either venous (standard) or capillary glucose levels (equal body fluid as used for calibration) were used as the reference in a CGM system calibrated with capillary glucose concentrations.…”

Clinical Implications of Accuracy Measurements of Continuous Glucose Sensors

“…ROC has also been shown to impact MARD. 21,22 Additional factors that impact the calculation of MARD include the absolute number of data points, their distribution, and missing data points. 13 Calibration, for most devices, is required both initially and at subsequent intervals to compensate for sensor ''drift.''…”