Dexcom and MM CGMS - 6 day BG comparison

Diabetes Technology Glucose Monitoring
1

I have used Dexcom for the past year, and prior to that used MM CGMS for 3+ years. I recently upgraded to MM Revel 523 pump, and wanted to test out the new features related to CGMS. I had an expired MM CGMS sensor, but decided to give it a try anyway.
For 6 days, I logged more Meter BGs than normal, and kept track of the Dexcom and MM sensor readings at the same time. Both were inserted on my stomach, to be as 'fair' as possible.


In general, my BG rises or falls gradually, and Dexcom usually shows the flat or slanted arrow, and rarely the single or double up/down arrows.

I was surprised the MM was 'closer' than I had remembered it being, prior to switching to Dexcom. But back then, I had been eating more 'white' carbs, and not pre-bolusing, so BG rises/falls were much faster. As a general rule, it makes sense that with the 20 minute lag, a 'flatter' trend would usually result in closer numbers.

I averaged the difference between the Meter BG and CGMS, as shown here.

Dexcom sensor ended up being very accurate after day 7, and I used it for 14 days total, a new record for me. Typically I use for 9-10 days. MM did not work at all on day 7, and ended with CAL ERRORs, and a very low ISIG.

So over the 6 days, the average difference between Meter BG and Dexcom was 13 points, while Meter BG and Minimed was 21.5 points. I did 12-15 Meter BGs/day, and did calibrations 3/day at the same time, with same number for both. All calibrations done when 'stable'.


And here are a couple comparisons.


In pic below, meter BG was 163, after a meal, so reasonable that Dex was showing a lag, and did climb to 160 within 20 min. But MM overshot the rise to about 180, and have no clue why it then dove to 95.


It seemed like Dexcom was better at catching the up/down trend sooner, and matched my expectations (based on bolus, food, exercise), and confirmed by meter BGs. So in general, I had more confidence in the trend information on Dexcom.

2

Thanks for the informative and detailed study! Despite the "small sample size" it says a lot!

3

MegaMinx ...just thinking at this moment, however would you allow me to forward the comparison to MM , Canada ?????

4

Thanks so much! That's very useful. I appreciate the effort you put into it, and wearing 2 sensors at once!

5

Thanks so much for this very informative post. It is very valuable to CGM users. Have you had the chance to use the Navigator CGM by Abbott? I used one that was loaned to me for a 3 day period, in Oct 2011. It was fantastic! never more than 12 points from my meter except when I had one meter readibg above 200. The Navigator gave a number considerably higher than the meter at that time. I found the Navigator to be much more accurate than my Dexcom, although I was not wearing both CGMs at the same time. It is too bad that the Navigator is not being sold in the US at this time. It is being sold in Europe. I have a friend who has used the Navigator for several years, and he praises it highly. He is the one who loaned me his Navigator when I visited Minneapolis for a diabetes expo.

6

Very informative! Thanks!

I've only used MM's CGM. Here is something that I've noticed. When I had my first MM pump and CGM I kept my pump programed to "on for the calibration" which was against what MM suggested. I just felt it was easier not to forget to calibrate. One less step. Well, when I recieved my new revel pump you can't leave it set to "on". So, it's my guess that since I have to calibrate at certain times and not "everytime" I check my bg, my CGM is a LOT more accurate. Usually, within 5-10 points. I'm not totally convinced that they have improved the sensors.