This CGM review will cover continuous glucose monitors from Dexcom and Medtronic. The Dexcom G4, and Medtronic Guardian. I’ve had the Medtronic Guardian since March of 2012. I got the Dexcom G4 at the end of December and started using it last week. First, let me just say that both have benefits and drawbacks compared to the other, however, I only trust 1 of them. If you’ve done any reading online about CGM’s you probably already know which one I trust.
I was excited in March to be getting the Guardian. At that time, I was only aware of the Guardian, and since it integrated directly with my pump, it was a no brainer to go with it. I just called Medtronic and they dealt with insurance, who paid for it all. (I have amazing insurance!) When I received it, I was a bit terrified at the size of the needle. So much so, that I told the Medtronic nurse I was going to send it back. She calmed my concern over it, and got me to try it. When I tried it, I was surprised that I barely felt it go into my skin. After using it for a week, I called the nurse again to ask why it was so horribly inaccurate. It was only ever close to being accurate in the mornings when I hadn’t eaten for 10 or 12 hours. Once it told me my blood sugar as 146, but it was really 322!!! I told her that if this is normal, it does me no good. She said that it’s not as accurate when I’m rising or falling quickly, when my blood sugar is high, or if I calibrate it more than 3 times a day. Well, it seems to me, that if it’s NOT accurate at those times, it’s no good to anybody? People under good control don’t need CGM’s. It’s the people on the blood sugar roller coaster that do, and if this CGM is admittedly inaccurate at those times, then what good is it? Again she convinced me to stick with it. 6 months later and I’m still on the original box of sensors, with multiple unopened boxes.
Then I started to become involved in the diabetes online community, or DOC. Everyone in the DOC raved about the Dexcom 7, with it’s comfort, accuracy, and that you can wear it for 7 days. In the fall, I suddenly remembered that someone at Medtronic told me I have to re-order transmitters every 6 months. Instead, I called Dexcom. The G4 had just been released to rave reviews. My insurance allowed it, and I got it ordered before end of year so there would be no out of pocket cost. (Deductible was complete early in the year.) So far, I’ve been absolutely thrilled with the Dexcom G4. It’s accuracy is especially surprising compared to the Medtronic, especially when I’m spiking or crashing quickly, or running high. My educator mentioned to me that it’s more accurate the more you calibrate it, so I’ve been doing that. In just 3 days I’ve already noticed trends that I could never notice on the Medtronic because it was so horribly inaccurate. I also like that it’s not integrated. It allows me to set it on my desk at work, and monitor my blood sugar easily, without having to stand up and dig my pump out of my pocket. I like that it’s brightly lit and in color so it’s easy to see in the dark, without my glasses on, when I feel low.
Over the last 2 days, I wore both sensors. Granted, the Medtronic was past it’s 6 month mark, but it was never any good new, so who cares. I was really just trying to prove to myself that I made a good decision this time. At every OneTouch meter test, the Guardian failed in comparison to the G4. Tonight, the G4 warned me of a low that I hadn’t noticed yet while the Guardian thought I was at 122. Before the 48 hour mark, I just gave up on the Guardian and tore it off my skin. I’m done with it. The Dexcom G4 I have complete trust in.
Now, there are some drawbacks to the G4, but they’re minor. What’s most important to me, and to anyone who needs a CGM, is accuracy, the the G4 is certainly impressive regarding it’s accuracy. Below I’ve listed the benefits and drawbacks to each CGM.
Dexcom G4 Benefits:
- Accuracy! Especially when you need it, when your blood sugar is changing quickly. It seems the more I calibrate, the more accurate it is
- Much thinner and more comfortable needle
- The transmitter doesn’t have to be charged because the battery lasts 6 months
- Not integrated into pump. I actually like it not being integrated.
- Color screen with red for lows, yellow for highs
- Better range. I can go anywhere in my apartment and not lose signal
- It shows blood glucose as high as 400 compared to Guardian which is only 250
- The site sticks to your skin before you plunge the needle in
- Can move forward and backward in navigation of blood sugar history
- Sensor lasts 7 days officially (14 unofficially), the Guardian only lasts 3 (6 unofficially)
- Multiple alert profiles with differing sounds
- You can adjust the rise and fall rate arrow alerts
- When you don’t get it calibrated on time, it keeps tracking instead of stopping
- Univeral USB charger and connection to PC to track data
Dexcom G4 Drawbacks:
- Manual insertion of the sensor needle (no insertion catapult, it’s like taking a shot, but it was super easy and I can live with that)
- The sensor sticks out away from your skin farther than the Guardian so it’s easier to catch on things (I’ve had no problems as of yet though)
- You can’t go back in history and see the actual blood sugar values. You can only see the graph
- Lots of plastic waste created each time you change a site. Every new site comes with a new insertion tool. Really seems like a waste of materials.
Medtronic Guardian Benefits:
- Ummmmm? Ummmm? Give me a minute. I’ll think of something.
- The guardian uses an automatic insertion catapult
- If you use a Medtronic pump, you only have to deal with 1 supplier
- Transmitter is smaller and doesn’t stick out as far from your skin as the G4
- Although I don’t consider it a benefit, most people would, but it’s integrated into your pump, so you only have to carry 1 device, which you’re already used to carrying
Medtronic Guardian Drawbacks:
- Horribly inaccurate. Sometimes more than 200% off. Often at least 100% off.
- Smaller range than the G4. If you’re in another room, chances are the signal will be lost.
- The insertion needle is *insert colorful metaphor* HUGE . . . and leaves bloody wounds/scars
- Integrated into pump. Which means you can’t leave it out on the desk at work, without having to stand up and dig your pump out of your pocket while you’re talking on the phone to a customer
- Transmitter has to be charged with a battery operated charger instead of universal USB cable
- Sensor only lasts for 3 days (6 days if you stretch it, but you’ll have a nasty wound if you do)
- Uses proprietary bluetooth connection to PC to track data, which is horribly slow and often doesn’t work, or has driver problems, etc.
- When you don’t get it calibrated on schedule, it TURNS OFF?!!!
When I started this blog, it was so others could learn from my mistakes and not have to suffer them. Please . . . learn from my mistake, buy the Dexcom G4. And now my typical closing tag from G.I. Joe is more appropriate than ever . . . . .
********** Now ya know, and knowing is half the battle. Go Joe!!! **********
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Hi Rich, just wanted to point something out that you mentioned above: “My educator mentioned to me that it’s more accurate the more you calibrate it, so I’ve been doing that.” The DexCom actually perfers WORSE if you calibrate more than 2 times in a 12 hour period. The DexCom technical support has mentioned this to me on more than one occation. You should only be calibrating it at MAX twice per every 12 hours (not including days when you are starting a new sensor). I usually only calibrate twice per day. Once when I wake up and once at dinner. That doesn’t mean don’t test, you can still test as much as you want, just don’t enter the result into the Dex each time.
I know that officially you’re only suppose to calibrate twice a day, but I’m actually having great results calibrating more often. I don’t know if I could psychologically handle only testing twice a day?! LOL! Thanks for the advice though. Maybe when I start my next sensor I try the twice a day calibration thing and see if there’s a difference.
Hi Rich! thank you for this review. all my doubts about Dexcom G4 vs Medtronic Guardian have been answered and I’ve made my choice. great review!
Glad I was able to help you decide. If you have questions after you get it, ask away. So this means your insurance has kicked in, right? That’s awesome.
Great review, thanks for taking the time to post. I know little about Medtronic, but also hadn’t seen a review from somebody on Dex G4 that wasn’t on Dex7. You brought up some different observations that I hadn’t thought of.
Some of those little observations are what I wanted to convey, because you won’t see those in normal reviews by review sites. They come from personal experience. I’m glad it helped.
Thanks for the comparison. I have been struggling to decide if I should stay with MM or switch to Dexcom over the past few weeks. I have used MM’s CGM for the past 4 years or so, but have never been particularly fond of it due to the reasons you mention! But I love that it is integrated as I prefer to “hide” my diabetes if possible and two things to have on me sounds like a lot. You do make a point though about the Dex receiver being separate and easier to look at. I have read a lot of online posts as well and of course the majority favor Dex.
I have been trying to research the Enlite sensor that MM is supposed to be releasing. I have found mixed things online about whether or not it has even been approved by the FDA yet and whether or not it will only be approved with their new pump that features low glucose suspend (called Veo in the UK). I even called MM today to inquire and they were as vague as ever. So if anyone has more info about Enlite I’d love to hear it!
Hi Jackie, and thanks for your comment. I don’t know anything about the Enlite sensor yet, but I know someone who might. My diabetes educator may know about it. She’s really savy about CGM’s because she’s type 1 and she tries them all so she can share with her patients. I’ll ask for you and comment when I know more. You know, I actually wrote an article last week about keeping your diabetes “top secret”. I don’t, as you can see. The whole world knows I’m diabetic. LOL!
Same thing here, I used both Medtronic and Dexcom, and thank God for Dexcom!!! (started out with Seven plus and now I have G4). What a huge difference! I wish all diabetics worldwide had the G4 covered! Some people can only still dream about it. It gives me some much more peace of mind. For example when I wake up in the morning being able to see that it has been steady all night. He’s not even that far behind at all anymore. Yesterday, my Dex was showing 166, I tested and it said 167. Amazing! I ran the Berlin marathon last September and that would’ve never been possible without my Dexcom. He’s next to my wonderful husband, my best buddy!
Nice to meet you! Yeah, I’m really loving my Dexcom. If only Dexcom made pumps! They actually announced a partnership recently with a pump manufacturer, so maybe we’ll see Dexcom integrated into a pump soon?
I like being able to see what it’s been all night too. My Medtronic I never trusted for that. The Dex is letting me fine tune my basals perfectly.
I don’t even like running down the block, although I love exercise, but just not a runner. Always amazes me to hear diabetic runners stories.
Hey Rich, just putting my 2 cents in.. I have actually not experience anything close to what you describe with the medtronic cgm. I have found mine to be accurate within 20 points at least 95% of the time. It is comfortable and i usually wear it for at least 6 days before changing. I can wait for the enlite to be available this year hopefully. Then bring on the closed loop system! Thanks for your opinion and for sharing your experience with the 2 cgms. Darci
Thanks Darci. Glad it works for someone.
We’ll see how the Enlite does when it’s released. If it’s more accurate, Medtronic could win me back in the hopes of a closed loop system . . . . . unless Dexcom and T-Slim beat them to it. 
Rich,
I also have used the Guardian for about 1 year now. I live in Australia and this is where Medtronic is testing the Enlite. It’s as useless as everything you wrote about with the exception of pain. It’s very painless although Often get some bleeding. I just removed a sensor today due to inaccuracy after 2 days.
I’m in the market for a new pump and Animas have their Vibe pump with the Dexcom G4 built in which I’m going to get after reading your post.
Many thanks.
Craig
Hi Craig, I’m glad you found my article helpful. You may want to look into the t-slim if it’s available in Austrailia, because if I remember right, they announced a partnership with Dexcom late last year. Good luck in your research!
Just plugged in my first sensor yesterday, and I must say loving it…
G4all the way………
Yep, I’m right there with ya Rita.
Wow… great to read all the reviews, I’m a bit of a CGM Virgin but I was undecided as to which was the bes CGM, I had narrowed it down to two the Medtronic or a Dexcom G4… well at least I have decided now, I’m going for the Dexcom G4!!
Now the only problem I have is if my Doctor will put me forward for one and if the NHS will pay for me to have one and pay for the cost of the weekly sensors/receivers.
If they say I can’t have a Dexcom G4 but I can have a Medtronic I think I’d rather not have one! lol I will have to see what the Doctor says when I see him. I will let you know how I get on.
Kind regards
Jo
I use both CGMs and I just started on dexcom. What I do (and it works on both) I only calibrate when my blood sugars are in a reasonable range (70-150) if it isn’t I discard the reading, correct and try again in 2 hours.
oh and medtronic CGM is like 6 years old now… I started using it in 2008, it is a little dated, eh?
Can you tell me if the British Dexcom G4 CGM will tell you the results in mmol/L as in the states your blood readings are between 110 & 150 for normal (I think) but in the UK our blood results for normal blood is between 4.0 & 7.0 so I’d obviously like to continue working with those figures, I would probably set a low reading at 3.5 and a high reading at maybe 10.0.
Thanks Rizzo for the above comments, I didn’t realise that the Medtronic was 6 yrs old so yeah you could say now, that it is definitely dated!
Cheers Jo
Sorry for the late reply. I wasn’t notified about these comments?! Ill have to check my blog settings. I’m pretty sure the British Dex would be in mmol.
Hi Rich,
Thanks for getting back to me, it was a great report that you wrote and I have found it to be really helpful.
I’m phoning my local hospital on Monday to see if I can make an appointment next time I’m home. (I work in Dominican Republic don’t go back home until July) hopefully I can find out if I’ll be eligible for a CGM then,
I will let you know how I get on.
Cheers Jo
Indeed, Rich is spot on with his comparison of the two products. I tried the Minimed 21.5 gauge harpoon for a couple of weeks and was not happy with it: being harpooned every 3-4 days, and having the pump, the sensor, and the transmitter taped on me I felt like a Borg (Star Trek).
I have used the Dexcom 7+ for about two years (same transmitter and reciever) without any issues, and I have found it good for up to 12-14 days. Transmitter broke recently, and the 7+ is being discontinued, so I will be upgrading to the G4 soon.
The reason I need a CGM is to deal with changing pump basal rates with the seasons, and I have no obvious hypoglycemic symptoms below 40 mg/dL, so CGM is critical : anyone else have issues with their basal rates and time of year? These change are not related to temperature or climate (I have traveled to the tropics without a need to make any pump changes, and flying across time zones requires that the pump clock remains unchanged (three weeks without any change of the clock). This would be a separate discussion, but has anyone else observed these conditions with their pump?
Hey Marc, thanks for the comment. I used to fly across time zones with my pump, and after being in the new zone for a day, I found that my blood sugars would get all screwed up if I didn’t change my clock on my pump to match the new time zone. I haven’t had to do that for years though.
Hi, I need to make [minor] adjustments to my basal rate every few months, though had not noticed weather, which I will try to watch and report back if I see that, which would be interesting!
I started seeing my insulin needs vary due to levels of stress and feeling supported or less so in my life. Yes, it’s girlie! But I had another girl tell me that after her Mom died she had higher insulin needs, and one doc told me that made sense, so I have considered stress/support important keys to keeping insulin needs lower, and necessary basal adjustments. Since marrying two years ago, I’ve needed to adjust my daily insulin totals, by about 35-40%, having adjusted both basals and my insulin-to-carb ratio just a smidge.
Regarding Rich’s time zone comment below, I found the same thing, having just moved from the US to Europe. It took my body about 2-3 days to fully adjust to the new time zone, blood-sugar-wise.
Hey Jennifre, you know exercising helps with stress right? Do you have a formal exercise program you adhere too? Even if it’s just walking a few times a week?
Hi, I have been using MM for just over two years, accuracy is horrible but I love the cgm concept. I live in Australia and have been using the enlite sensors are relatively painless but not accurate. I really want to hear more about the Symphony tcgm and the laser cgm but those appear to be some distance in the future. In the process of checking out DexG4 now. Hopefully get one after a one sensor trial, if that’s possible.
Thanks for the info
Hello Lloyd! I can’t say enough good things about accuracy for the Dexcom. It’s so accurate I feel totally safe with it, knowing that I don’t have to question it’s readings. You should definitely call your local Dexcom office to get that trial you mentioned.
I have a Dexcom G4 and LOVE IT. I tried the MM CGM that goes with my pump and the inaccuracies just didn’t make it worth it. It did help me figure out some trending, but it never alerted me to lows in a timely fashion. The G4 has been simply amazing. Low alerts have almost entirely been spot on and even the high warnings have been surprisingly accurate.
I’m glad you found the Dexcom. I know it’s helping me a great deal more than the Medtronic did.
I am seriously considering the switch from Mm to Dexcom G4.
Although I have vanity to consider because the Dexcom size. But as many other D’s had mentioned accurate readings is the key. Lets see what my insurance says. Thanks for your help.
Yeah, ditch the medtronic, and get the dexcom. Life will be so much better. Regarding vanity, my dexcom makes me way more attractive.
Love my G4. My sensors last 4-5 weeks, easy, no scaring, no issues, other than the sticky (which I tape down regularly). The MORE you calibrate, the better it is. I suspect anyone being told different, is not being told correct information.
4-5 weeks?!!! I’ve ever tried that? The tape is always falling off after 2 weeks for me, even with extra clear medical tape on top of the sensor. Its still accurate for that long eh? Interesting.
In about 5-7 days I will find out if my insurance will cover the G4. I’ve never had a CGM or a pump so this is all new to me. I really hope I can get the G4 because I think it would make life much easier. I am a constant tester. I run out of test strips every month and have to pay out of pocket for extra. Reading this really made me more confident with my decision of pursuing the G4.
I’m glad it helped you feel better.
I just came from an endo appointment and I told my endo that I TRUST my G4, and I feel naked without it now. He told me he wants me to test more with my meter anyway. LOL! There really isn’t a need though. My G4 has never been wrong. EVER. In contrast, my Medtronic Guardian that I used to have was rarely ever right about my blood sugar. 
I truly hope your insurance will cover it for you, because it can make a world of difference. Good luck!