New monitor reduces reliance on fingersticks

A new device that could alleviate bothersome fingerstick testing for your adult diabetic patients is under review by the FDA. The GlucoWatch monitor, developed by Cygnus in Redwood City, CA, is worn on the wrist and painlessly measures glucose levels through the skin by iontophoresis — sending tiny electric currents through the skin — even while patients are sleeping. It sounds an alarm if patients’ blood sugar hits dangerous levels.

Investigators recently showed the device to be as accurate as invasive serial blood glucose measurements when they enrolled 92 diabetic patients to wear the wrist device for half a day while also performing two fingerstick blood glucose measurements per hour on them.1 The participants received varied diet and insulin during the study to produce a wide range of glucose levels. Investi gators report that the device accurately tracked blood glucose levels in the range of 40 to 400 mg/dL, and note that the iontophoretic readings lagged behind the fingerstick measurements by 18 minutes. But they add that the frequent, automatic, and noninvasive measurements obtained with the wrist device provide continual access to information about glucose levels.

The FDA says the device sometimes gives erroneous readings. Twenty-five percent of the time, readings can differ from blood tests by about 30%, meaning if the reading is a glucose level of 150, it might really be anywhere from 135 to 165. In addition, it won’t measure if the patient’s arm becomes too sweaty, and it is less effective at detecting very low glucose than very high levels. Because of the potential for error, patients never should decide to use insulin based on a GlucoWatch monitor measurement without first double-checking with a fingerstick test, FDA advisers and Cygnus agree. To use the prescription-only device, patients slide a thin plastic sensor onto the watch’s back each time they strap it on. Small electric currents extract a tiny portion of glucose from fluid in skin cells instead of blood, measuring it every 20 minutes for 12 hours.


1. Tamada JA, Garg S, Jovanovic L, et al. Noninvasive glucose monitoring comprehensive clinical results. JAMA 1999; 282:1,839-1,844.