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

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 < or =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.