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> 7 day real time Comparison of Medtronic vs Dexcom , Posted by Brian Tubbs on another Forum. Copied with his permission.
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The following is a comparison of the Medtronic CGMS and the Dexcom 7

These results are only for 7 days, and only performed on one person.
It is likely that the CGMS's could perform differently for different
people. Therefore, the following information is not intended to say
which devise is better than the other, but to merely share our

My daughter Kendall (age 6) wore both the Medtronic CGMS and the
Dexcom 7 CGMS from August 1, 2008 August 7, 2008. Both units were
inserted into her backside and she wore both units at the same time
for the full 7 days. During this time we attempted to test often and
record the reading off of both CGMSs and her Onetouch meter. We also
attempted to record which CGMS alarmed first for highs and lows. Due
to various activities and Kendall being 6, we did not catch all
alarms, or test BG at all instances.

With 67 reading over the 7 day period (where we have readings for
Dexcom, Medtronic and Onetouch), the Dexcom was approximately 21%
more accurate (10 points). For determining accuracy, I took standard
deviation of the variances of the CGMSs from the Onetouch meter.

Dexcom: std=36.7
Medtronic: std=46.5

Both CGMS were over 100 points low two times during the test. One of
the two times, they were both off by more than 100 points at the same

The Dexcom had 13 instances where the CGMS was 50 points or more
lower than the Onetouch meter.

The Medtronic had 14 instances where the CGMS was 50 points or more
lower than the Onetouch meter.

The Dexcom had 5 instances where the CGMS was 30 points or more
higher than the Onetouch meter.

The Medtronic had 11 instances where the CGMS was 30 points or more
higher than the Onetouch meter.

We had a number of alarms through the test period; however, we did
not always record Kendall's BG with the Onetouch, therefore we could
not tell if the alarm was true or false. The following is some of
the high alarms that we received that had a BG recorded.

In two instances Dexcom was the only alarm to give us a high alarm.
One time both CGMSs gave a high alarm at the same time. Three times
Dexcom alarmed first and then Medtronic alarmed later. The advanced
times were 15 minutes (once); 30 minutes (once); and 45 minutes

In no instances did the Medtronic give a high alarm first. This is
given the caveats mentioned above.

Four times the Dex was the only CGMS to give an alarm (this could
have been because we treated and BG rose prior to Medtronic giving an
alarm). One time Medtronic was the only CGMS to give an alarm.
One time Medtronic alarmed first by 10 minutes. Four times Dexcom
alarmed first (5, 15, 20, 30).

From a user stand point, the Medtronic (in my opinion) is far
superior. The Dexcom falls short in that:
- Can not see actual historical numbers without computer. (if
you are looking at the dots, and you see that your last dot is lower
than the previous dot, you do not know if it is 5 pints lower {60
points an hour trend} or 20 pints lower {240 points an hour trend})
- Can not see when that last alarm occurred.
- Can not see when the next calibration is needed. This could
then sneak up on you and required a 2 am update.
- Can not see the sensor age.
- More difficult to enter Meter BG
- Rechargeable battery. This is good in that you will save
battery costs; however, if it goes low while out, you can not just
- Lack of transmitter memory. The Medtronic transmitter can
store up to 20 minutes of readings, so if you get separated from the
receiver, you will be able to the past 20 minute readings. This is
good for swimming, or forgetfulness.

After posting those results, Brian was asked a question and he provided this additional comment:

We currently own the Medtronic. The Dexcom was on loan to us.

The lack of user functionality on the Dexcom is a big negative.
However, the Dexcom did seem to leave less trauma on the body when

If you never had a CGMS, then you would not miss the functionality
provided by the medtronic. Thus the Dexcom might be preferable due
to greater accuracy on Kendall.

I hope that Animas (the pump we currently use), builds in the user
functionality when it is incorporated into their pump in mid-2009.

Last update: Aug 21 2008, 05:10 PM by Linda B    Created: Aug 21 2008, 05:10 PM by Linda B    Views: 926
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