Guardian vs. DexCom, and More CGM Smarts

First off, I wanted to clear up any misconceptions about my perspective on Medtronic’s Guardian RT continuous glucose monitoring system versus the DexCom. Many of you came away from my first post with the impression that I prefer the DexCom (Seven). Not true. So far I’m finding the Guardian easier to use and more accurate than the Dex. A few details to elaborate:


* I find the Guardian much less fussy to wear and use. Actually, the sensors on both systems are pretty small and comfortable. But as noted, calibration on the Guardian does NOT require hooking up the unit to a particular traditional meter. DexCom is slated to do away with that requirement in its next version, but for now, you’re stuck switching to the OneTouch and hooking the two up via cable at least four times a day.

The compact size of the Guardian receiver and built-in belt clip make it easy to wear on your person as well. The DexCom’s carrier was always floppy, so I ended up sticking the unit in my purse most of the time, which meant I was always walking out of range and disrupting the transmission between the sensor and receiver. The alarms are much softer and less intrusive on the Guardian, too. That was a major issue for me personally — and my husband, when the darn thing was beeping like a semi truck in our bedroom all night long. And have I mentioned batteries? The DexCom has to be plugged into the wall like a cell phone for charging, which of course interrupts your usage. The Guardian, on the other hand, just requires a quick AA battery switch.

* I’m also finding the accuracy with the Guardian to be much more consistent. Yes, it still misses some highs and lows in “real-time,” but it’s not so wildly off-target that I’m ready to toss it out the window, which was often the case with my Dex. I have learned that some of this may have had something to do with my calibration skills (see below). In addition, the Guardian receiver offers much more data you can use. For example, you can actually scroll through your individual glucose readings over the last 5 hours. And you see 3, 6, 12 and 24-hour views, versus only 1, 3, and 9-hour views with the DexCom. As noted earlier, you can also input carb counts and insulin doses on the Guardian for detailed record-keeping.

On top of all this, the Medtronic rep spent a good deal of time explaining calibration to me. I thought I knew it all, but being reminded about the 10-20 minute lag time between plasma blood (at your fingertips) and interstitial fluid was actually enlightening. The rep reminded me also how important it is to calibrate ONLY when your glucose levels are stable, otherwise you’re just setting up the CGM system for inaccuracy.

Author and nutrition expert Hope Warshaw has written an excellent article in Diabetic Living magazine called (ah-ha!) “Ready for Prime Time? Continuous Glucose Monitoring.” She provides a refreshingly realistic overview of the ups and downs of using this new technology. See her “Terms to Know” for some straightforward lessons on calibration, interstitial fluid, lag time, and warm-up time. Great info!

Hope’s sage advice:

When you start using your CGM, take it slow and be patient. Use the numbers as a way to keep track of trends rather than as a signal to enact an immediate response. Focus on fixing one problem at a time and don’t let yourself get overwhelmed. Be realistic in your expectations. Continuous glucose monitoring won’t produce perfect glucose control, and it doesn’t remove the daily challenges you face in managing your diabetes.

Amen. Thank you, Hope.


10 Responses

  1. kassie
    kassie February 25, 2008 at 7:36 am | | Reply

    did you ever use the dexcom 7? Or are your comments limited to the older version?

  2. David Edelman
    David Edelman February 25, 2008 at 8:06 am | | Reply

    Amy, I really appreciate your comments. Elizabeth’s Realtime is coming any day now. I’ve taken the warning about calibration to heart. Please keep sharing your observations.

  3. AmyT
    AmyT February 25, 2008 at 8:45 am | | Reply

    I’ve used both the Dex 3 and the 7. Just updated that in the post to clarify.

  4. Bernard Farrell
    Bernard Farrell February 25, 2008 at 9:42 am | | Reply


    Thanks for another useful post, especially the pointer to Hope’s article.

    I have a minor correction re the Dexom. On the first day of a new sensor you need to calibrate with two fingersticks and then 12 hours later. So on the first day it’s 3 or maybe 4 fingersticks. On a normal day you only need to hook the two up with the way-too-long-cable twice a day.

    So it’s not QUITE as bad as you make out. I’m still eagerly waiting for the new one.

  5. AmyT
    AmyT February 25, 2008 at 10:56 am | | Reply

    Bernard, my endo recommended 4x/day for calibrating the Dex.

  6. whimsy2
    whimsy2 February 25, 2008 at 8:16 pm | | Reply

    How much does the Guardian cost? How much are the sensors and how long do they last?

  7. MoHo
    MoHo February 25, 2008 at 9:11 pm | | Reply

    Different strokes for different folks, I had the exact opposite of what you experienced. It seems like one or the other works for people, I’m glad you found which one is better for you. For me the MM missed critical drops that the DC caught (and continues to.) I do with the DC had a clip, I emailed this idea to them about a year ago and was blown off, hopefully they’ll listen to you!

  8. Bob
    Bob February 26, 2008 at 10:12 am | | Reply

    I’ve also had the opposite experience. For me, the Dex is much more accurate and longer lasting than the Medtronic. But it does seem to vary from individual to individual. Either system is better than none.

  9. Andy
    Andy February 26, 2008 at 11:12 am | | Reply

    Hi !
    About cost… I don’t know how much are sensors (I think they are 35 EUR/piece) and sending device is around 1000 EUR (prices are for Europe). I don’t know how much Guardian Device is, since I have just wanted to use sensors and sending device with pump (which I don’t have yet, but I talked with rep for Minimed on friday, so I know what I am talking about… at least I think so).

  10. camille johnson
    camille johnson February 29, 2008 at 12:36 pm | | Reply

    Well, I just got off the phone with a different DexCom7 rep and he convinced me that I don’t have to hire a lawyer to be treated sanely by the company. Really, I’ve only had one bad egg but he had a very visible position so his bad behavior really made the company look bad. I’m not completely sold on this machine — I think it is unnecessarily tricky, and complicated (and why can’t they ATTACH a belt hook?) Everything about it is frustruating. BUT I’m willing to try, try again because I want the 7-day version over the 3-day.

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