Saturday, August 27, 2011

Dueling CGMS

Today marks my 13th day experimenting with a new CGMS - the Dexcom 7 Plus. I didn't think I could be converted from my beloved Freestyle Navigator after 2 years and 10 months of loyal service, but I've been playing "Dueling CGMS" and find that it's a fair trade-off. I'll discuss this in detail in a minute...

I have been meaning to write this post for some time. Accompanying it was to be a flurry of photos comparing readings from my Omnipod PDM, my Navigator, and my Dexcom.

Then I dropped my iPhone 3GS into a gutter and it swam in sewage for two days before a drainage crew fished it out. The photos did not survive. (And I'm using a go phone until the new iPhone comes out.)

So here it is...the good, the bad, and the ugly. Just without fun comparison shots.

Navigator still impresses, as I thought it would, in one of key three areas in which I was testing it - the range between the receiver and transmitter. Dexcom 7+ is certainly an improvement over the trial Dexcom 7 I used on loan from my endocrinologist's office 3 years ago, but I still feel like I have to lug the receiver from room to room. It's far too large to wear comfortably for me right now, but at least it picks me up if I'm not touching it (unlike the D7 I tried).
SCORE: Nav 1, Dex 0

I expected Navigator to win in overall accuracy, and I won't lie - it does, BUT I found that Dexcom's claim for better accuracy in the low range was spot on. Dexcom can detect that I'm 43 mg/dL when I'm 42 mg/dL. (And it did.) Navigator isn't that tight in the lower range, but it continually beat Dexcom with rising blood sugars. Overall, I find that Dexcom is a little hypersensitive to rising numbers, assuming often that I'm as much as 100 mg/dL higher than I actually am. Case in point: I was getting in the car to drive somewhere, tested on my PDM and it read 189. Navigator showed me 183 and holding. Dexcom was just sure I was 231 and rising. Another time, Dexcom read that I was 250 when I was 160. I feel it may give me more of a sense of failure, honestly, because the peaks are much steeper. But you've got to appreciate its algorithm and shorter lag time, too. When I'm more stable, it's very accurate.
SCORE: I'm going to call this one a tie, which puts us at Nav 2, Dex 1

Comfort. I really remembered Dexcom's sensor wire being less comfortable than I'm finding it now. Granted, maybe they made an improvement between the Dex 7 that I tried and the Dex 7+ - anyone know? I'm delighted that I can't feel it in either of the two locations I've tried. I find insertion to be equally comfortable/painful to that of the Navigator, but it is much more convoluted. Navigator was simple to insert one-handed. I had a tough time getting Dexcom on my arm by myself (on my stomach, it was simple). And while the transmitter is a tiny little thing, it takes up about the same amount of space as Navigator once you consider the adhesive, which is much better adhesive than the Navigator's adhesive.
SCORE: I'm actually going to give this one to Dexcom. Nav 2, Dex 2

Software. Easy. Dexcom wins this. Though I'm a Mac user, I can easily run the Dexcom software on Parallels. The Dexcom software is not quite as good as CoPilot, but I haven't been able to upload my Navigator in 19 months because CoPilot for Navigator is absolutely incompatible with Win7, which I installed the week before I went into the hospital to give birth to Sweetie. I begged one of the CoPilot engineers to fix this known issue. That was only 3 months after I discovered the problem. They can bite me. What good is a CGMS when you and/or your medical team can't review the data?
SCORE: Nav 2, Dex 3

But...I hate that Dexcom doesn't allow me to review standard deviation, averages, or high/low values immediately on the receiver. Navigator puts it on board. I'm not going to give Nav extra points for this though because I'm that ticked about not being able to use their software.

Alarms. They both have predictive alarms, but I sincerely appreciate being able to set some to vibrate on Dexcom rather than Nav's choice of low/med/high volume beeps. What I will miss about the Navigator though is the ability to mute all alarms (except lows) with a single button sequence. Before a performance the other day, I felt like it was a huge chore to go into five separate areas to turn high alarms, low alarms, rising alarms, falling alarms, and out of range and other alerts to vibrate. Navigator lets you mute all alarms for one hour, but it will breakthrough for low alarms and sound them anyway. At least I can put those on vibrate with Dexcom. And I prefer Dexcom's snooze alert. Navigator constantly beeping every few minutes when I'm already high and cranky sometimes sends me hurling it across a room...not to mention my friend R's point that it can also cause you to overtreat with subsequent boluses or glucose because of the too frequent reminders about a high or low.
SCORE: Toss-up. Nav 2, Dex 3

Calibration. Navigator asks for 4 calibrations in 5 days. Dexcom asks for 14 calibrations in 7 days. Navigator has a built-in meter for calibrating. Dexcom doesn't. This one goes to Nav.
SCORE: Nav 3, Dex 3

Backlight. Navigator asks for a button sequence to activate the backlight. It has to be done when the receiver is in sleep mode - can't be done from any of the active screens. And if you hit the wrong buttons, say in your sleep in the dark, you have to wait for the screen to go to sleep again before trying a second time. It's SO frustrating. Dexcom activates the backlight whenever you view the screen. Thank you, Dexcom.
SCORE: Nav 3, Dex 4

Additional Info. My Navigator transmitter fell off twice in the 5 days I ran it against Dexcom, which stayed safely and snugly attached to my belly. It fell off because I'm using a broken transmitter that the company can't replace due to a "supply interruption" that is quickly approaching its second year. Unacceptable. They have the transmitters. They have the receivers. They don't have the legal right to manufacture them due to bureaucratic BS. So there they sit in a warehouse (or so I imagine). Sensors expiring, customers asking questions that remain unanswered, Abbott not caring because the Navigator represents a tiny tiny percentage of the 6% of their company that is Diabetes Care. They're much too busy producing Similac and other big money products. They let go of all of their sales people for the Navigator and have basically tucked their tails between their legs. Dexcom gets extra points for being a reliable, focused company with their customers' best interests at the forefront.
SCORE: Dexcom wins.


  1. This was a great post. We use Dex intermittently...our first CGM experience was in 2008 with Nav, though.

    I had a hard time with it...I had sworn off CGM forever, but eventually came around to giving Dex a try late last year.

    When she's wearing Dex, we're really happy with it...most of the time. Oddly enough, though, Dex causes ME more anxt. It's another thing to worry about -- is it accurate, is the adhesive holding up okay, where's the receiver?

    If she had her way, we'd never use the CGM. Her school nurse LOVES the CGM. So we meet in the middle...and it works for us, I guess.

  2. Ms Lee, we just purchased a DEXCOM 7+ for our nine year old son with Type 1. To our chagrin we only learned after the purchase of how it isn't mac compatible

    We did find freeware called Wineskin that allows you to run PC software on a Mac, but now we've found that when you plug in the unit with the USB Cable, the software doesn't detect the monitor.

    I see you use Parallels to use the DEXCOM software. Was there anything special you had to do to enable the USB connection to interface with the software? Does my question even make sense?

    Thanks for your post and whatever insight you might be able to share

    Patrick Lafferty, father of Seamus (9)
    Dallas, TX

    1. Patrick, I'll have to ask my husband for details. We've since upgraded to the newest OX and can no longer use our current version of Parallels, so I'm not sure what solution my husband has come up with yet.