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Accuracy Study of the Medtronic Minimed Continuous Glucose Monitoring System (CGMS) and GlucoWatch ® G2 TM Biographer (GW2B) in Children with Type 1 Diabetes – A GCRC-based study. Abstract #156. Background: DirecNet. Di abetes Re search in C hildren Net work

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Abstract #156

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Accuracy Study of the Medtronic Minimed Continuous Glucose Monitoring System (CGMS) and GlucoWatch® G2TM Biographer (GW2B) in Children with Type 1 Diabetes – A GCRC-based study

Abstract #156


Background: DirecNet

  • Diabetes Research in Children Network

  • NIH funded collaborative study group

  • 5 clinical centers, central laboratory, coordinating center, and representatives from NICHD and NIDDK

  • Objective: to critically evaluate the clinical usefulness of current and future glucose sensors in children and adolescents


Goals of Present Study

To determine the accuracy of the CGMS and G2B

  • During hypoglycemia and hyperglycemia

  • Over a broad age range in pediatrics

  • Comparing nighttime to daytime readings

  • Determine if accuracy changes as sensors age


Devices used – GW2B

  • GlucoWatch 2 - Cygnus

  • Two hour calibration

  • Provides a glucose reading every 10 minutes

  • Data can be generated for up to 13 hours

  • GlucoWatch glucose lags serum glucose by 17.5 minutes and this lag was adjusted for in assessing accuracy

  • For details of study see Poster #432


Devices used - CGMS

  • Medtronic Minimed

  • Functions up to 72 hours

  • Data from subcutaneous glucose is stored and retrospectively reviewed

  • In 11/02 the sensor manufacturing process was modified

    • We studied 115 “original” and 25 “modified” sensors

  • For details of study see Poster #387


Methods

  • All subjects admitted to a GCRC for ≈ 24 hours

  • Sensors calibrated to a home glucose meter

  • Serum glucose levels sent to a central lab

  • Samples every hour during the day, and every ½ hour from 9 PM to 7 AM

  • Samples every 5 minutes for up to 90 minutes following insulin induced hypoglycemia

  • Samples every 5 minutes for 1 hr following meal induced hyperglycemia


Subject Demographics

  • 91 Children and Adolescents

  • 51% Female

  • 43% Pumpers

  • Mean HbA1c = 7.8%


Young Subject Wearing Devices


Example of data generated from CGMS use


Graphic example of data generated from GlucoWatch 2


Measures of Accuracy

  • Pearson’s correlation

  • Relative absolute difference (RAD) %

    • |(sensor – reference)/reference| x 100%

  • ISO criteria (proposed)

    • Reference glucose ≤75 mg/dL

      • Sensor value within ±15 mg/dL

  • Reference glucose value >75 mg/dL

    • Sensor value within ±20%


Overall Accuracy Results

ISO Criteria: If reference glucose ≤ 75 mg/dL, sensor glucose within ± 15 mg/dL;

if reference glucose > 75 mg/dL, sensor glucose within ± 20%.


Factors NOT Impacting Accuracy For Either the GW2B or CGMS

  • Age of the Subject

  • Time of Day (Nighttime vs. Daytime)

  • BMI (body mass index)

  • Location of GW2B placement

    • Upper vs lower arm

    • Inner vs outer arm


Effect of Glucose Concentration on Accuracy Assessed by Median RAD%


GW2B Function By Hours Of Use

Sensor age had no effect on CGMS function


Sensitivity and False Positive rate for detection of hypoglycemia (<60 mg/dl)


Adverse Events

  • GlucoWatch

    • Minor skin irritation in 29% of GW2B uses

    • No severe or persistent skin reactions

  • CGMS

    • No significant skin irritation or site infections


Summary

  • GW2B accuracy was unaffected by site of wear

  • The GW2B was less accurate in the last 4-5 hours of use, whereas CGMS accuracy was unaffected by sensor age

  • When compared to the original CGMS, the modified CGMS was more accurate in all measures


Summary

  • For both the GW2B and the CGMS:

    • Subject age had no effect on accuracy

    • Time of the day had no effect on accuracy

    • Accuracy was greater for hyperglycemia than for hypoglycemia

    • Neither device is as accurate as currently available meters


  • Yale University

    • William Tamborlane

    • Stuart Weinzimer

    • Elizabeth Boland

  • University of Minnesota Central Laboratory:

    • Michael Steffes

    • Jean Bucksa

    • Maren  Nowicki

  • Jaeb Center for Health Research

    • Roy Beck

    • Katrina Ruedy

    • Craig Kollman

    • Andrea Booth

    • Gladys Bernett

  • Barbara Davis Center

    • H. Peter Chase

    • Rosanna Fiallo-Scharer

    • Jennifer Fisher

  • University of Iowa

    • Eva Tsalikian

    • Michael Tansey

    • Linda Larson

  • Nemours Children’s Clinic

    • Tim Wysocki

    • Nelly Mauras

    • Kristen Gagnon

  • Stanford University

    • Bruce Buckingham

    • Darrell Wilson

    • Jennifer Block


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