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Head to Head Comparison

The Dexcom STS and the Paradigm RT continuous monitors are currently available in the U.S. with a prescription. In this study, they are compared head to head while being worn by one person with Type 1 diabetes. Over 33 days, 262 simultaneous readings were compared between a One Touch meter and the two continuous monitors. The meter was used to calibrate both monitors and as the standard against which their accuracy was evaluated.

Is one monitor better than the other? How close are the monitor readings to the Ultra fingerstick readings? Find out by viewing the comparison slideshow, downloading the Powerpoint presentation or reading below. Be sure to comment or read others' comments about this study in our forums.

A Method For Comparison Of Two Continuous Monitors

by John Walsh, P.A., C.D.E.

Various approaches are available to measure the accuracy and utility of continuous monitors and to compare one monitor with another. The Clarke error grid, developed in 1987, has been widely used to verify the accuracy of fingerstick meters and was initally used also to validate continuous monitors. This grid compares a glucose value from a lab value, YSI instrument, or glucose meter with a simultaneous glucose value from a continuous monitor. Unfortunately, this comparison does not show glucose trend information, nor the timeliness that high and low glucose warnings provide.

Other attempts measure values like area under the curve (AUC) within glucose graphs and compare this to frequent standard glucose tests, done every 5 minutes or so. Some information is provided by comparing.

Dexcom STS and Paradigm RT screens compared

I bought a Dexcom STS sensor and have been wearing it ever since. When the local Medtronic representative asked if I would like to try the Paradigm RT pump/sensor combo, I jumped at the chance and have worn both sensors side by side for over three weeks now. This article covers my initial impressions of the pros, cons, and accuracy of each sensor. For comparison to my actual blood sugar readings and calibration, I used a One Touch Ultra meter properly coded for the strips in use. During this time, I have averaged just under 10 fingerstick tests a day (136 tests in the last 14 days) with an average reading of 130 mg/dl.

I usually leave my Dexcom sensors in place for 6 to 9 days which is longer than the company's recommended 3 days. My experience shows that these sensors work this long. However, most of the Paradigm RT sensors were used for only 3 to 5 days because I had not tested them sufficiently to trust that they would perform longer than 3 days (Others have reported that they will.). In the first column of the spreadsheet below, the teal color shows when the Paradigm RT sensors were changed. The Dexcom sensors were changed less often as indicated by the light blue color in the second column. In this limited sample, length of use did not appear to affect accuracy in either sensor.

The Dexcom is slickly packaged and the Paradigm comes in its traditional pump packaging. The combination of a pump and sensor make the Medtronic more appealing in terms of one less device needed. The Dexcom currently has no connection with any of the current insulin pumps. Glucose results from the Paradigm RT are not used for any bolus or other dose calculations in the Paradigm pump, so the Dexcom is as useful whether combined with injections or a pump.

The con mon readings of individual blood sugars and the trend lines from the Paradigm RT appear on the Paradigm pump screen. This means only one device is needed on the belt or in the pocket. But this con mon data does not enter the pump's data. Readings still have to be manually entered in the pump so the pump can recommend bolus doses.

Accuracy Of Readings And Trends

Date Time Ultra Sensor A Sensor: B
28-Sep
17:58
128
83
112
28-Sep
18:06
130
127
170
28-Sep
18:48
135
118
150
28-Sep
19:19
74
69
112
28-Sep
19:34
56
54
95
28-Sep
19:52
58
50
65
28-Sep
21:43
69
79
96
29-Sep
0:11
94
110
138
29-Sep
0:55
231
163
158
29-Sep
1:32
201
122
220
29-Sep
8:46
114
63
166
29-Sep
11:27
229
144
224
29-Sep
15:17
181
165
112
29-Sep
16:14
82
87
104
29-Sep
16:37
60
67
90
29-Sep
20:08
129
131
80
29-Sep
21:37
149
160
110
29-Sep
22:52
205
217
118
30-Sep
10:24
86
60
114
30-Sep
11:19
150
136
168
30-Sep
15:37
75
77
76
30-Sep
16:46
95
116
74
30-Sep
19:33
88
97
46
30-Sep
20:29
57
68
44
30-Sep
23:14
105
128
112
1-Oct
7:25
278
294
272
1-Oct
11:27
152
176
122
1-Oct
23:12
153
183
156
1-Oct
15:18
125
126
176
2-Oct
20:31
95
95
128
2-Oct
21:18
60
54
84
2-Oct
21:24
51
43
78
2-Oct
22:34
91
77
82
3-Oct
9:13
125
169
100
3-Oct
10:19
168
195
122
3-Oct
12:59
129
131
162
3-Oct
14:07
92
104
140
3-Oct
14:29
67
77
116
3-Oct
19:58
176
191
212
3-Oct
20:24
159
181
210
4-Oct
7:11
122
115
106
4-Oct
22:06
205
211
76
5-Oct
12:52
127
108
136
5-Oct
13:34
97
80
110
5-Oct
15:39
93
78
98
5-Oct
16:57
101
96
74
6-Oct
0:11
149
153
104
6-Oct
8:29
88
80
98
6-Oct
11:27
68
71
80
6-Oct
11:39
59
55
76
6-Oct
20:55
81
82
80
7-Oct
8:33
118
122
120
7-Oct
11:15
212
218
202
7-Oct
12:39
129
141
144
7-Oct
13:09
149
162
130
7-Oct
13:42
217
210
164
7-Oct
15:38
103
141
126
7-Oct
18:02
146
128
96
7-Oct
18:52
187
176
136
8-Oct
8:37
102
86
128
8-Oct
8:55
87
80
116
8-Oct
16:22
80
82
104
8-Oct
20:17
211
250
164
8-Oct
20:42
273
249
196
8-Oct
22:17
341
344
358
9-Oct
8:38
150
134
162
9-Oct
15:51
65
62
80
9-Oct
17:17
205
219
172
10-Oct
3:23
297
230
188
10-Oct
19:26
78
84
88
10-Oct
19:36
100
94
80
10-Oct
21:12
97
134
98
11-Oct
11:30
171
148
138
11-Oct
11:48
181
172
160
11-Oct
12:24
117
80
148
11-Oct
12:35
92
53
144
11-Oct
13:58
94
80
106
11-Oct
19:03
166
166
118
11-Oct
19:53
136
107
114
11-Oct
20:45
128
133
108
11-Oct
21:54
139
167
108
12-Oct
11:30
73
93
122
12-Oct
11:42
68
78
114
12-Oct
12:33
99
74
98
12-Oct
13:39
76
77
90
12-Oct
13:53
63
43
80
12-Oct
14:05
86
69
76
12-Oct
15:21
137
139
124
12-Oct
17:07
142
158
108
12-Oct
20:16
138
123
108
12-Oct
20:41
134
137
140
13-Oct
8:01
82
107
108
13-Oct
9:39
119
161
98
13-Oct
10:31
112
148
116
13-Oct
10:58
85
109
104
13-Oct
11:17
108
105
98
13-Oct
11:28
157
163
102
13-Oct
11:50
218
231
130
13-Oct
12:17
164
219
164
13-Oct
12:40
158
192
150
13-Oct
13:17
117
119
134
13-Oct
13:48
81
79
102
13-Oct
15:40
252
234
142
13-Oct
16:08
282
280
144
13-Oct
17:03
286
276
166
13-Oct
17:58
208
206
140
13-Oct
19:32
82
80
80
13-Oct
21:43
137
123
92
14-Oct
14:39
92
80
144
14-Oct
14:54
80
61
112
14-Oct
19:26
109
93
74
14-Oct
10:01
99
92
120
15-Oct
7:38
81
77
112
15-Oct
9:10
158
156
162
15-Oct
11:14
63
78
112
15-Oct
12:59
100
114
142
15-Oct
15:35
85
78
92
15-Oct
16:03
63
53
84
15-Oct
16:15
58
40
78
15-Oct
17:18
83
48
70
15-Oct
18:05
108
110
116
15-Oct
18:56
154
163
140
15-Oct
19:20
209
221
162
15-Oct
23:09
173
175
152
16-Oct
8:20
150
141
134
16-Oct
9:55
227
217
164
16-Oct
12:33
166
178
130
16-Oct
13:06
192
199
152
16-Oct
13:27
192
197
154
Average
 
131.5426
129.938
124.6822
St. Dev.
 
58.56
59.81
41.38
MAD/Avg. Deviation
47.02
49.28
31.92
1st detect BG < 80
13 (+3)
1 (+3)
1st detect BG > 160
12 (+4)
0 (+4)
More than 50 mg/dl off
5
19

In general, today's continuous monitors are better at helping the wearer see the trend in their blood sugar than in giving an accurate glucose value at a particular time. None of today's monitors is capable of nor approved for relying on the readings for treatment decisions such as a correction bolus or eating carbs. In this test, numerous daily fingersticks were done to compare the two sensors to actual glucose values.

For testing, I induced both high and low readings to find out how each system responds to changes in glucose and to verify the speed and accuracy of their responses. As can be seen in my blood sugar spreadsheet on the right, neither sensor can yet be used to replace old-fashioned fingersticks, although the Dexcom comes close to achieving this.

For onscreen data, the Dexcom provides a larger screen display (1.19 versus 0.86 square inches for pixel to pixel display) and a larger glucose graph display (1.38 versus 0.47 square inches). The Dexcom display screen with its white background also has more brightness and contrast than the green background of the Medtronic. The upside for the Medtronic is that it has a smaller profile (see photo) and weighs only one more ounce (roughly 4 oz. versus 3 oz.) with its built-in pump.

Because of the previous basal and bolus adjustments I made over several weeks while wearing the Dexcom, I set the alerts on each sensor to 80 mg/dl for lows and 160 mg/dl for highs to trigger low and high alerts without needing to induce too much excursion in my blood sugars. I set up the experiment as a head to head test to find out which sensor would alert first when my blood sugar was going high or low. I would then read the other sensor and compare each to the acutal glucose at the time. At times, I would let my blood sugar continue to fall or rise until the other sensor gave an alert to see how much delay was involved, and to better estimate their accuracy at low and high readings.

Note for comparison purposes in the picture above that both sensors show horizontal lines for the selected targets of 80 and 160 mg/dl. The readings of 93 and 122 compare to an actual blood sugar of 73 mg/dl on the Ultra meter at the time of the picture. Note also how differently the same 3 hours of glucose values appear in the two sensors. For reference, an hour and 43 minutes earlier, about midway back on the graph, my blood sugar had risen to 290 mg/dl (actually 289 and 291 on two tests taken less than a minute apart to verify accuracy), after starting at 125 mg/dl some 3 hours and 16 minutes before the picture was taken.

As in the picture above, the Dexcom turned out to be the hands down winner for accuracy and trending. It proved to be much closer to actual blood sugars throughout the three weeks of testing. As can be seen in the spreadsheet, the Dexcom readings reflect the actual blood sugar more accurately with faster tracking of the speed and direction of blood sugar changes. It was not uncommon to have the Dexcom give a low or high alert 15 to 60 minutes before the Paradigm RT when the blood sugar was rising or falling.

In detection of lows, the Dexcom STS won by a landslide. The STS was the first sensor to detect the blood sugar going below 80 mg/dl, as indicated by the red colored boxes, on 14 occasions compared to only one for the Paradigm RT. On three additional occasions, both sensors gave an alert at approximately the same time. When the blood sugar rose above 160 mg/dl, as indicated by the yellow colored boxes, the Dexcom was the first to detect the change on 12 occasions compared to two occasions for the Paradigm RT. There were five additional occasions where both sensors gave an alert at about the same time.

Glucose errors are indicated by the purple boxes in the speadsheet. I crudely estimated errors as any sensor reading that differed by more than 50 mg/dl from the One Touch Ultra reading. Again in a landslide win, the Dexcom made only 4 errors with 3 of these by one sensor, while the Pardigm RT commited 18 errors that were about evenly spread among 6 different sensors.

The Paradigm system would certainly be convenient in incorporating a continuous monitor readout into an insulin pump so one less device would need to be carried around. But in this limited sample of one, this convenience appears to be more than offset by the RT's inaccuracy and its slow response to changing readings. After a few days of simultaneous use, I found I was automatically checking the Dexcom to estimate my current glucose and referring to the RT mostly out of curosity. From these limited results, I cannot at this time recommend the RT system. I was, however, pleasantly surprised by the relative accuracy of the Dexcom STS sensor. (Spreadsheets are a wonderful thing -- I, for one, would tend to miss the overall positive results after mentally cursing the occasional misses!)

As far as disclosure, I have no stock or direct financial ties to either company. I have one indirect connection to Dexcom in that I work part-time for North County Endocrine in Escondido, CA, where Dr. Timothy Bailey has done a limited amount of clinical trial work on the Dexcom sensor. I am listed as a "subinvestigator" in some of these studies, but I have insufficient benefit and no bias as a result of this indirect connection. I paid full price out of my own pocket for my Dexcom continuous monitor and sensors, while the Pardigm RT pump and sensors were kindly loaned/donated to me by Medtronic. Medtronic's 522/722 Paradigm pumps have been very reliable insulin delivery systems, but the current RT sensor appears to need additional work. Both companies, and others such as Abbot with their Navigator system, are making rapid progress in sensor technology and monitoring systems. Look for more head to head comparisons as soon as these improvements become available.

Companies: 

Updated date: Mon, 04/21/2014 - 15:40

  • Updated date: Mon, 04/21/2014 - 15:40

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