Evaluation of the CGMS Gold® Using a Standardized Test
Brian R Hipszer, PhD, Jung-Won Park, MD, Jeffrey I Joseph, DO
Results
The minimum, maximum, and mean number of paired
values per subject were 86, 131, and 108. The
average maximum and minimum blood glucose
concentrations were 183 ± 24 and 41 ± 4 mg/dL and
the average range was 142 ± 21 mg/dL. The
minimum, maximum, median, mean and standard
deviation of the correlation coefficients are 0.3251,
0.9597, 0.7422, 0.7386 and 0.1831.
Conclusions
The correlation coefficient has not been widely used
as a measure to assess the CGM accuracy because it
is sensitive to the glycemic range under which the
CGM is evaluated. However, if the test is
standardized, any CGM can be evaluated and
compared.
Further Discussion
The standardized test described here was used to
evaluate accuracy of continuous glucose monitors. It
has been reported that continuous interstitial glucose
monitoring is inaccurate when the change in blood
glucose is greater than 1.5 mg/dL/min (1) or glycemic
levels are below 70 mg/dL (2). As such, this
standardized test includes two periods of controlled
glucose change and two periods of hypoglycemia.
References
1. The Diabetes research in children network study
group (DirecNet). Evaluation of factors affecting
CGMS calibration. Diabetes Technology &
Therapeutics. 2006;8:318-25.
2. DirecNet. Accuracy of the modified continuous
glucose monitoring system (CGMS®) sensor in an
outpatient setting: Results from a diabetes research in
children network (DirecNet) study. Diabetes
Technology & Therapeutics. 2005;7:109-14.
40
180
36
160
32
140
28
120
24
100
20
80
16
60
12
200
40
8
160
20
4
120
800
0
0
40
60
120 180 240 300 360 420 480 540 600
0
0
8
16 24 32 40
Time (min)
200
40
180
36
160
32
140
28
120
24
100
20
80
16
60
12
200
40
8
160
20
4
120
800
0
0
40
60
120 180 240 300 360 420 480 540 600
0
0
8
16 24 32 40
Time (min)
200
40
180
36
160
32
140
28
120
24
100
20
80
16
60
12
200
40
8
160
20
4
120
800
0
0
40
60
120 180 240 300 360 420 480 540 600
0
0
Sensor Current (nA)
200
Sensor Current (nA)
Paired reference/sensor data were collected in twelve
subjects. In each subject, the blood glucose was
manipulated in a predefined manner using
intravenous infusions of insulin and dextrose. Each
reference value was the average of two plasma
glucose concentrations measured simultaneously on
both channels of the YSI 2300 Stat Plus (Yellow
Springs, OH) using a single venous blood sample.
Blood samples were obtained at alternating intervals
of two and five minutes. The sensor’s output current
from the CGMS Gold (Medtronic Diabetes,
Northridge, CA) was recorded every five minutes.
Spline interpolation was used to pair each reference
value in time to a corresponding sensor value using
Matlab (Mathworks, Natick, MA). Any data pairs
recorded in the 60 minutes after sensor insertion were
not analyzed. The correlation coefficient was
computed for each subject.
R
0.3251
0.9548
0.7372
0.7077
0.8431
0.7472
0.8537
0.6391
0.5530
0.6474
0.9597
0.8951
8
16 24 32 40
Time (min)
Sensor Current (nA)
Methods
n
123
131
119
124
112
107
93
99
86
91
104
110
Reference Glucose (mg/dL)
We investigated the accuracy of the Medtronic CGMS
Gold® under a standardized glycemic pattern.
Subject
1
2
3
4
5
6
7
8
9
10
11
12
Reference Glucose (mg/dL)
Objective
Reference Glucose (mg/dL)
Thomas Jefferson University, Philadelphia, PA 19107, 2. Drexel University, Philadelphia, PA 19104