Accuracy of the Modified Continuous Glucose Monitoring (CGMS®) Sensor in an Outpatient Setting: Results from a Diabetes Research in Children Network (DirecNet) Study

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Abstract
Objective: We previously reported the results of an inpatient accuracy study in children with type 1 diabetes using the Continuous Glucose Monitoring System (CGMS®, Medtronic MiniMed, Northridge, CA). During the course of that study, a new process was implemented for manufacturing the CGMS sensor. Accuracy from the resulting modified sensor used by only 14 children was significantly better than the original version [median relative absolute difference (RAD), 11% vs. 19%; P < 0.001]. Baseline data from a subsequent outpatient study provide an opportunity to further assess the accuracy of the modified sensor in a much larger sample of children with type 1 diabetes. Research Design and Methods: As part of a randomized trial to assess the utility of the GlucoWatch® G2™ Biographer (Cygnus, Inc., Redwood City, CA), 200 children with type 1 diabetes were instructed to wear a CGMS for 48–72 h in an outpatient setting at baseline. Glucose measurements from a OneTouch® UltraSmart® (Lifescan, Inc., Milpitas, CA) home glucose meter were downloaded and used as reference values to calculate accuracy measures. Results: The overall median RAD was 12%. Accuracy was better during hyperglycemia than during hypoglycemia (median RAD, 10% vs. 20%; P < 0.001) and on optimal versus non-optimal days but did not vary significantly by the number of calibrations entered. Conclusions: These data confirm the improved accuracy previously reported for the modified version of the CGMS sensor.