Accuracy of the GlucoWatch G2 Biographer and the Continuous Glucose Monitoring System During Hypoglycemia

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Accuracy of the GlucoWatch G2 Biographer and the Continuous Glucose Monitoring System During Hypoglycemia
2004
Diabetes Care

© 2004 by the American Diabetes Association, Inc.

Emerging Treatments and Technologies
Original Article

Experience of the Diabetes Research in Children Network
*The Diabetes Research in Children Network (DirecNet) Study Group

From the Jaeb Center for Health Research, Tampa, Florida

ABSTRACT

OBJECTIVE—The goal of this study was to assess the accuracy of the GlucoWatch G2 Biographer (GW2B) and the continuous glucose monitoring system (CGMS) during hypoglycemia in children and adolescents with type 1 diabetes.

RESEARCH DESIGN AND METHODS—During a 24-h clinical research center stay, 91 children and adolescents with type 1 diabetes (aged 3.5–17.7 years) wore one or two CGMSs, and 89 of these subjects wore one or two GW2Bs. Frequent serum glucose determinations were made during the day, overnight, and during insulin-induced hypoglycemia resulting in 192 GW2B reference pairs and 401 CGMS reference pairs during hypoglycemia (reference glucose <=60 mg/dl).

RESULTS—During hypoglycemia, the median absolute difference between the 192 GW2B reference glucose pairs was 26 mg/dl and between the 401 CGMS reference glucose pairs was 19 mg/dl with 31 and 42%, respectively, of the sensor values within 15 mg/dl of the reference glucose. Sensitivity to detect hypoglycemia when the GW2B alarm level was set to 60 mg/dl was 23% with a false-alarm rate of 51%. Analyses suggested that modified CGMS sensors that became available in November 2002 might be more accurate than the original CGMS sensors (median absolute difference 15 vs. 20 mg/dl).

CONCLUSIONS—These data show that the GW2B and the CGMS do not reliably detect hypoglycemia. Both of these devices perform better at higher glucose levels, suggesting they may be more useful in reducing HbA1c levels than in detecting hypoglycemia.

Abbreviations: CGMS, continuous glucose monitoring system • CRC, clinical research center • DirecNet, Diabetes Research in Children Network • GW2B, GlucoWatch G2 Biographer

INTRODUCTION

Hypoglycemia remains a major obstacle to successful treatment of type 1 diabetes, especially in children. In adolescents with type 1 diabetes, the risk of severe hypoglycemia is greatly increased compared with adults, regardless of the intensity of treatment (1). In young children with type 1 diabetes, there are heightened concerns that hypoglycemia will cause permanent neurologic sequelae (2,3). Across all age-groups, the possibility of a severe hypoglycemic event occurring at school, at play, or at night is one of the greatest fears of patients and parents alike (4).

The introduction of near-continuous glucose monitors represents a technologic advance that may be particularly useful in the management of youth with type 1 diabetes. Two such devices are currently FDA approved: the GlucoWatch G2 Biographer (GW2B) (Cygnus, Redwood City, CA), which provides real-time measurements of interstitial glucose concentrations at 10-min intervals, and the continuous glucose monitoring system (CGMS) (Medtronic MiniMed, Northridge, CA), which stores glucose values obtained every 5 min for a retrospective review. The GW2B is equipped with an alarm to signal hypoglycemia and pending hypoglycemia as well as hyperglycemia. The accuracy of the GW2B has been reported in several studies (5–10), but data in children are limited (11), and prior studies have not systematically evaluated sensor function during acute hypoglycemia. There have been several reports of frequent and prolonged hypoglycemia during the night when using the CGMS (12–15). However, recent studies have raised questions regarding the accuracy and reproducibility of the CGMS (15–17).

The purpose of this study is to report the accuracy of the CGMS and GW2B during hypoglycemia occurring either spontaneously or during an insulin-induced hypoglycemia test in children with type 1 diabetes.

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