Abstract 156
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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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Abstract 156

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

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

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

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

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

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

Subject Demographics

  • 91 Children and Adolescents

  • 51% Female

  • 43% Pumpers

  • Mean HbA1c = 7.8%


Young subject wearing devices

Young Subject Wearing Devices


Example of data generated from cgms use

Example of data generated from CGMS use


Graphic example of data generated from glucowatch 2

Graphic example of data generated from GlucoWatch 2


Measures of accuracy

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

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

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

Effect of Glucose Concentration on Accuracy Assessed by Median RAD%


Gw2b function by hours of use

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

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


Adverse events

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

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


Summary1

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


Accuracy study of the medtronic minimed continuous glucose monitoring system cgms and glucowatch g2tm biographer gw2b i

  • 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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