Detection of Hypoglycemia With the GlucoWatch Biographer

Abstract

OBJECTIVE -Hypoglycemia is a common acute complication of diabetes therapy. The GlucoWatch biographer provides frequent and automatic glucose measurements with an adjustable low-glucose alarm. We have analyzed the performance of the biographer low-glucose alarm relative to hypoglycemia as defined by blood glucose Յ3.9 mmol/l. RESEARCH DESIGN AND METHODS -The analysis was based on 1,091 biographer uses from four clinical trials, which generated 14,487 paired (biographer and blood glucose) readings.RESULTS -The results show that as the low-glucose alert level of the biographer is increased, the number of true positive alerts (alarm sounds and blood glucose Յ3.9 mmol/l) and false positive alerts (alarm sounds but blood glucose Ͼ3.9 mmol/l) increased. When analyzed as a function of varying low-glucose alert levels, the results show receiver operator characteristic curves consistent with a highly useful diagnostic tool. Setting the alert level from 1.1 to 1.7 mmol/l above the level of concern is likely to optimize the trade-off between true positives and false positives for each user. When the same blood glucose data are analyzed for typical monitoring practices (two or four measurements per day), the results show that fewer hypoglycemic events are detected than those detected with the biographer.CONCLUSIONS -The frequent and automatic nature of the biographer readings allows more effective detection of hypoglycemia than that achieved with current medical practice. Diabetes Care 24:881-885, 2001H ypoglycemia is a common acute complication of diabetes therapy. The frequency of severe hypoglycemia has been shown to increase with more intensive treatment. Increasing the frequency of glucose measurements, regardless of the technique used, makes it possible to detect a greater number of hypoglycemic events. However, as many as seven glucose measurements per day may fail to detect hypoglycemic events (1).A device providing automatic readings could make frequent monitoring easier and enable an alarm to be sounded in response to glucose readings below userselected alert levels. Such an alarm could reduce the risk of hypoglycemia, making intensive therapy safer and more acceptable for patients. The GlucoWatch biographer (Cygnus, Redwood City, CA) provides frequent, automatic, and noninvasive glucose measurements-up to three readings per hour for as long as 12 h after a blood glucose measurement for calibration. Clinical studies in controlled and home environments have demonstrated high accuracy and precision (2,3). The results presented here evaluate the hypoglycemia alert performance in a large and demographically diverse patient population using the biographer both in controlled and normal daily environments. The accuracy and precision results from these studies have been described (4).The performance of the hypoglycemia alert depends on the selection of a low-glucose alert level that will trigger an audible alarm. The performance of the alert function can be best evaluated by an analysis of the receiver operator characteri...

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