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Comparison of the Numerical and Clinical Accuracy of Four Continuous Glucose Monitors

¹ University of Virginia, Charlottesville, Virginia
² Profil Institute for Metabolic Research, Neuss, Germany

Corresponding author: Boris Kovatchev, PhD, University of Virginia Health System, Box 800137, Charlottesville, VA 22901. E-mail: boris{at}virginia.edu

OBJECTIVE—The purpose of this study was to compare the numerical and clinical accuracy of four continuous glucose monitors (CGMs): Guardian, DexCom, Navigator, and Glucoday.

RESEARCH DESIGN AND METHODS—Accuracy data for the four CGMs were collected in two studies: Study 1 enrolled 14 adults with type 1 diabetes at the University of Virginia (UVA), Charlottesville, Virginia; study 2 enrolled 20 adults with type 1 diabetes at the Profil Institute for Metabolic Research, Neuss, Germany. All participants underwent hyperinsulinemic clamps including 1.5–2 h of maintained euglycemia at 5.6 mmol/l followed by descent into hypoglycemia, sustained hypoglycemia at 2.5 mmol/l for 30 min, and recovery. Reference blood glucose sampling was performed every 5 min. The UVA study tested Guardian, DexCom, and Navigator simultaneously; the Profil study tested Glucoday.

RESULTS—Regarding numerical accuracy, during euglycemia, the mean absolute relative differences (MARDs) of Guardian, DexCom, Navigator, and Glucoday were 15.2, 21.2, 15.3, and 15.6%, respectively. During hypoglycemia, the MARDs were 16.1, 21.5, 10.3, and 17.5%, respectively. Regarding clinical accuracy, continuous glucose–error grid analysis (CG-EGA) revealed 98.9, 98.3, 98.6, and 95.5% zones A + B hits in euglycemia. During hypoglycemia, zones A + B hits were 84.4, 97.0, and 96.2% for Guardian, Navigator, and Glucoday, respectively. Because of frequent loss of sensitivity, there were insufficient hypoglycemic DexCom data to perform CG-EGA.

CONCLUSIONS—The numerical accuracy of Guardian, Navigator, and Glucoday was comparable, with an advantage to the Navigator in hypoglycemia; the numerical errors of the DexCom were 30% larger. The clinical accuracy of the four sensors was similar in euglycemia and was higher for the Navigator and Glucoday in hypoglycemia.

Abbreviations: CG-EGA, continuous glucose–error grid analysis • CGM, continuous glucose monitor • EGA, error grid analysis • ISO, International Standards Organization • MAD, mean absolute difference • MARD, mean absolute relative difference • MedAD, median absolute difference • MedARD, median absolute relative difference • P-EGA, point–error grid analysis • R-EGA, rate–error grid analysis • UVA, University of Virginia

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