GlucoWatch G2 Biographer alarm reliability during hypoglycemia in children

Abstract

Background: The GlucoWatch G2 Biographer (GW2B) (Cygnus, Inc., Redwood City, CA) provides near-continuous monitoring of glucose values in near real time. This device is equipped with two types of alarms to detect hypoglycemia. The hypoglycemia alarm is triggered when the current glucose measurement falls below the level set by the user. The "down alert" alarm is triggered when extrapolation of the current glucose trend anticipates hypoglycemia to occur within the next 20 min.

Methods: We used data from an inpatient accuracy study to assess the performance of these alarms. During a 24-h clinical research center stay, 89 children and adolescents with Type 1 diabetes mellitus (3.5-17.7 years old) wore 174 GW2B devices and had frequent serum glucose determinations during the day and night.

Results: Sensitivity to detect hypoglycemia (reference glucose < or = 60 mg/dL) during an insulin-induced hypoglycemia test was 24% with the hypoglycemia alarm alone and 88% when combined with the down alert alarm. Overnight sensitivity from 11 p.m. to 6 a.m. was 23% with the hypoglycemia alarm alone and 77% when combined with the down alert alarm. For 16% of hypoglycemia alarms, the reference glucose was above 70 mg/dL for 30 min before and after the time of the alarm. For the two alarm types combined, the corresponding false-positive rate increased to 62%.

Conclusions: The down alert alarm substantially improves the sensitivity of the GW2B to detect hypoglycemia at the price of a large increase in the false alarm rate. The utility of these alarms in the day-to-day management of children with diabetes remains to be determined.

Figures

Figure 1

Sensitivity during Insulin-induced Hypoglycemia Test by Alarm Type. Sensitivity defined as percent of hypoglycemic cases when the GW2B alarmed.

Figure 2

Overnight Sensitivity and False Positive Rates by Alarm Type. Sensitivity defined as percent of hypoglycemic episodes where the GW2B alarmed within ± 30 min. False positive rate defined as the percent of alarms where the reference glucose was continuously > 70 mg/dL from 30 minutes prior to 30 minutes after the alarm.