1. 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

2. 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

3. 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

4. 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

5. 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

6. 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

7. Subject Demographics 91 Children and Adolescents 51% Female
43% Pumpers
Mean HbA1c = 7.8%

8. Young Subject Wearing Devices

9. Example of data generated from CGMS use

10. Graphic example of data generated from GlucoWatch 2

11. 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%

12. Overall Accuracy Resultsn r
Mean RAD
Median RAD
within ISO
GW2B
3,672
0.86
22%
16%
60%
CGMS (original)
5,658
0.77
26%
19%
53%
CGMS (modified)
1,120
0.90
11%
72%
Ultra
2,068
0.97 9% 6%
94%
ISO Criteria: If reference glucose ≤ 75 mg/dL, sensor glucose within ± 15 mg/dL;
if reference glucose > 75 mg/dL, sensor glucose within ± 20%.

13. 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

14. Effect of Glucose Concentration on Accuracy Assessed by Median RAD%

15. GW2B Function By Hours Of Use
< 4
4 to <8
≥ 8 p
Median RAD
15%
19%
0.002
Sensor age had no effect on CGMS function

16. “Alarm” Setting (mg/dL)
Sensitivity and False Positive rate for detection of hypoglycemia (<60 mg/dl)
“Alarm” Setting (mg/dL)
Sensitivity
False Positive Rate
GWB
CGMS Original
CGMS Modified
CGMS
Modified 60
23%
36%
49%
51%
63%
58% 80
59%
67%
84%
68%
64%
100
85%
100%
80%
76%
75%
120
92%
91%
83%

17. Adverse Events GlucoWatch CGMS
Minor skin irritation in 29% of GW2B uses
No severe or persistent skin reactions
CGMS
No significant skin irritation or site infections

18. 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

19. 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

20. 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
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