On day 1 I set the rules. On day 2 I talked about CGM insertion. Today I will discuss usability and reveal some results.

Home Screen:

Both Dexcom’s have similar home screens showing time, trend, current BG, battery, scale, BG goal (range-the dotted lines). The G4 adds times along the graph and loses the 1, 3, 6, 12 or 24 hour label.

The major difference is Dexcom added a color screen to the G4. Both screens are back litDexcomCompare1

Medtronic’s CGM has most of the same information with the addition of insulin left in the pump (as it is also an insulin pump. Medtronic does make a version of their CGM without the insulin pump). To get to the home screen you press the ESC button. It has a backlight that can be turned on and off at will. The graph is a little less useful as there are no numbers on it. One useful thing it does have is the ability to scroll through the history of the graph.

Put your mouse over the image below to see the History screen.

All three devices have the ability to view the graph in 3, 6, 12 or 24 hour intervals. Dexcom can also show a 1 hour graph. I find 3 and 24 the most useful. 3 hours lets me know what is going on and helps me predict what will happen next. The 24 hour graph is a nice way to see how the past day has been.

Device menus:

The two Dexcom CGM’s have almost identical menus. Lets start by going over the similarities.

Pressing any button on a Dexcom turns the screen on. The 7+ comes on instantly. The G4 takes about 1.5 seconds. That doesn’t sound like a big deal but after getting used to the 7+ and now having to wait I find it a bit annoying (maybe I am being too picky). When the screens turn on you are brought immediately to the trend graph (unless you have been given an alert, in which case it shows the alert first, then the graph). Pressing the center button on the G4 or the OK button on the 7+ brings you to the menus.

Dexcom’s G4 adds the menu category, Profiles where you can chose whether you want your device to vibrate or beep and how loud you want the beep. I find the G4′s beeps much more annoying than the 7+ which is a good thing when I am sleeping and it is trying to wake me up from a low.

Both Dexcom systems are intuitive to navigate through. You want to enter a BG, click “Enter BG”; want to see the trend graph, click “Trend Graph.” The one feature I never use is events. You can record carbs, insulin, exercise and health (like an illness, stress, alcohol etc.) Those events then show up on the graph when you download your data (I’ll show that in a future post).

Medtronic’s menu is a little more involved as it is part of an insulin pump but offers a few upgrades. Any time you enter a BG in the bolus wizard it asks if you want to use the number to calibrate. You can also calibrate manually.

To get to the sensor menu you scroll down to “Sensor” from the main menu. From there you find all of your options: Calibrate, Alert Silence, Link to Sensor, Edit Settings, Calibration History, Sensor Alert History, Review Settings and Turn off Sensor.

I will go over a few of my favorite features.

Alert Silence is my a great feature. (When I was getting trained on the pump my trainer asked me, “How much do you want it to yell at you?” after I started the CGM.) If I know, for example I have high blood sugar and don’t need to be reminded for say 5 hours, I can silence the alert for that long.

Calibration History and Sensor Alert History are also quite useful. I often forget when I last calibrated. The device reminds you as you get close to 12 hours without calibration but this way I can check. Sensor Alert History is a quick way to see when I was low or high.

Pros and Cons of each:

Medtronic’s CGM/pump is always attached to you. That makes it hard to forget it. It also makes it a little harder to delve into the menus in the middle of the night without glasses.

Both Dexcom units are standalone devices. That lends itself to being left around the house. With the 7+ that can be an issue. I often loose signal if I am in another room. The G4 has been working for me 2 floors away.

Having fewer devices to carry (Medtronic) is a plus. I prefer to have my CGM easily accessible when I am driving, biking, running, etc. (Dexcom). I have seen people Velcro their Dexcom to their car’s steering wheel or the handlebars of their bike.

Medtronic is working on several accessories to go along with their CGM. Along with Ford, they showed off an in car glucose monitoring. They have already brought MySentry, an alarm clock like remote glucose monitor to market.

The Numbers:

Features and usability aside it all comes down to the numbers. How accurate are the CGMs?

First, I will say that these results are from one person (me) with one sensor each over a three day period so far. That said, the results are typical of what I have seen over the past few months using each.

In the first 72 hours I tested mu BG 45 times; roughly once every hour or high/low alert while awake (yes, I missed a few. I’m human).

In that time here are the accuracy reports.


Closest to actual out of 45 readings: Winner Dexcom G4

Dexcom 7+ was the closest 42% of the time

Dexcom G4 was the closest 47% of the time

Medtronic Revel was the closest 16% of the time


First to alert to a high or low (and be correct): Tie between Dexcom G4 and Medtronic*

Dexcom 7+ : 11 times

Dexcom G4 : 12 times

Medtronic Revel : 12 times

*There were two occasion where Medtronic’s CGM didn’t alert to a low at all. The G4 and 7+ caught them. I tested then treated and no other alert went off.


What is your goal in using a CGM? If it is to see where your BG is at all times then the G4 is clearly the way to go. If you are on a 7+ it may be worth the upgrade. Take a closer look at the data I collected so far (below).

If your goal is to be alerted when (or before) you have a low or high it is a harder decision. All three are neck in neck. Medtronic’s predictive alerts have caught lows before I even felt it though sometimes it tells me I am going to be low and I am not. I would rather that then not being warned at all (which as I mentioned did happen). I find Dexcom’s trend arrows more useful then Medtronic’s in seeing how fast I am falling or rising but more on that in a future post.