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Glucose sensors perform poorly in small study; companies provide data to the contrary.

SEATTLE -- Neither the GlucoWatch G2 biographer (Cygnus) or the Continuous Glucose Monitoring System (Medtronic MiniMed) appears to be accurate enough to provide normative glycemic levels in nondiabetic children, Dr. Nelly Mauras reported at the annual meeting of the Pediatric Academic Societies.

"While preliminary reports and anecdotal evidence suggest that nondiabetic children have low sensor glucose levels, especially at night, such findings may in fact represent inaccurate glucose measurements," said Dr. Mauras, chief of the division of endocrinology in the department of pediatrics at Nemours Children's Clinic, Jacksonville, Fla.

In a multicenter study funded by the National Institutes of Health, Dr. Mauras and her associates enrolled 11 boys and 4 girls aged 7-17 years with a normal body mass index and no family history of type 1 diabetes. The children wore the sensors and blood was sampled for 24 hours using an indwelling catheter every hour during the day and every half-hour from 9 p.m. to 7 a.m. The ideal standard blood glucose range was defined as 81-100 mg/dL.

Blood glucose concentrations measured by the GlucoWatch deviated from the standard by an average of 15 mg/dL. About 40% of the values were within 10 mg/dL of the target.

Blood glucose concentrations measured by the Continuous Glucose Monitoring System (CGMS) deviated from the standard y an average of 21 mg/dL. About 34% of the values were within 10 mg/dL of the target, Dr. Mauras reported at the meeting, which was sponsored by the American Pediatric Society, the Society for Pediatric Research, and the Ambulatory Pediatric Association.

The GlucoWatch and the CGMS recorded 7% and 3% of the nighttime values less than 60 mg/dL, respectively Over 24 hours, the GlucoWatch and CGMS recorded falsely high values (greater than 160 mg/dL) 1% and 3% of the time, respectively.

In an interview, Neil Ackerman, Ph.D., chief technical officer of Cygnus Inc., said the company has never claimed that the GlucoWatch is the standard for measuring blood glucose. "It doesn't make blood measurements in the same manner" as an indwelling catheter and a lab blood analyzer, "but we believe that the device will assist in the maintenance and control of diabetes in a children's population."

Dr. Ackerman cited results from a randomized trial of 40 children aged 7-17 years with type 1 diabetes in poor glucose control: 20 wore the GlucoWatch biographer for a 3-month period and 20 did not. Hypoglycemia was detected more frequently in the GlucoWatch group than the control group (Pediatrics 111[4 Pt. 1]:790-94, 2003).

After the first 3 months, the group using the GlucoWatch to monitor glucose levels in addition to conventional therapy had significantly lower average Hb[A.sub.1c] levels than the control group.

According to a response to Dr. Mauras' study prepared for this newspaper by Medtronic MiniMed, the majority of the data used in the study was collected using CGMS glucose sensors that have been superseded by a new manufacturing process.

"An abstract presented [in February 2003] at the Second La Jolla Conference on Glucose Monitoring and Control clearly demonstrated that manufacturing process changes in the Medtronic MiniMed glucose sensor [after November 2002] led to significant improvements in accuracy, as measured by the mean absolute difference between the sensor and standard blood glucose readings," the statement read.

The mean absolute difference was significantly reduced in newly manufactured sensors (11.4%) versus older sensors (15.8%). Medtronic MiniMed sponsored the study.
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Title Annotation:Clinical Rounds
Author:Brunk, Doug
Publication:Pediatric News
Geographic Code:1USA
Date:Aug 1, 2003
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