Continuous glucose monitoring is becoming better and better, but still isn’t without flaws. Here I’ll compare 2 systems currently on the market–the Dexcom Seven Plus and the Guardian RT.
Minimed Guardian RT (left) and Dexcom Seven Plus (right)
Sensor Insertion
The Minimed’s insertion is simpler and and more straight forward, but I like the Dexcom insertion better. First of all, the way the Dexcom’s inserter is designed, it is much more difficult to mess up with the angle and the insertion needle is more likely to enter the skin fully. With the Guardian, if I was at all hesitant when pressing the trigger, it wasn’t uncommon for the insertion needle to only make it half way in. Overall, the Dexcom may be a little less painful, but they are quite similar in that respect. It is much more difficult to remove the insertion device and connect the transmitter on the Dexcom, so this may make it less favorable for those wanting to place the sensor in harder to reach areas.
Transmitter/Sensor design
As far as the design of the transmitter and sensor go, both systems have advantages and disadvantages. The Dexcom adhesive patch is much better than the Guardian. So far, it has been totally unnecessary to use any type of dressing that was necessary to make the Guardian transmitter/sensor stay on. The Dexcom’s adhesive patch is larger overall, but worth the size in my opinion given that it is much more secure. Plus, once you put Tegaderm or IV3000 over the Guardian’s sensor, it’s going to cover a larger area. As far as I can tell, the Dexcom’s transmitter doesn’t have a battery. My assumption here is that there is a small battery attached to the sensor…? To me this is an advantage because it takes off an extra 30 minutes of waiting every time the sensor is changed. Major drawback on the Dexcom is the the transmitter has no memory. This is something I didn’t consider before purchasing the device. If the receiver is not in range, quite simply, you are losing precious data. On the other hand, the Guardian’s transmitter stores 45 minutes of data, so you don’t lose anything as long as you get back in range of the receiver within 45 minutes. As far as range, the signal strength is about the same on both devices.
Receiver design
The Guardian is a clear winner for me as far as the receiver goes, however, both leave much to be desired. The larger screen on the Dexcom may be attractive to some, and the larger case unattractive. Unfortunately, to me, it seems that the larger screen is there for no reason. That is, they aren’t making good use of it. The graph on the Dexcom shows a range of 40-400 on the y-axis, so even if all of your readings are between 80 and 120, you’re stuck looking at a graph with a vertical scale of 40-400. A waste of screen space? Tell me about it. So if your eyes are bad, don’t let the larger screen lure you in. Additionally, on the Dexcom, there is no way to view specific data points on the graph. The Guardian has a cursor that allows you to scroll through the data points on the graph. Lastly, the Dexcom receiver also needs a 3 hour charge every 3 days. Now why in the world they would do this is beyond me. Perhaps they picked the wrong area to go green. I tried letting it charge overnight, but the transmitter signal didn’t make it to my night stand which cost me a whole night of data.
Sensor Wear Length
Dexcom advertises a 7 day sensor wear that I have decided is bogus. In reality, Dexcom sensors don’t last any longer than the Minimed sensors. What does this mean for the user? It means that you are paying more for a sensor that is going to last the same amount of time. As far as I can tell, these are essentially the same sensors Dexcom was selling when they only had an indication for 3 day wear.
Accuracy
To be honest, I don’t have much to say here. From what I can tell, accuracy of the two devices is very similar. With the Dexcom, I sometimes get one data point that’s way off of the others (ie noise), but that’s rare enough for me to ignore. For both devices, accuracy is highly dependent on where and how the sensor is placed, but personally, I have found the Guardian to be a bit more reliable.
Calibration
Dexcom is the winner here. It doesn’t just stop giving you data if you don’t calibrate within a 12 hour period. Just a notification that it needs to be calibrated. The Guardian forces you to calibrate at 12 hours which is a nuisance especially if it happens to be at a time that isn’t ideal for calibration, such as during a high or a period of rapid blood glucose movement.
Software
Carelink (Minimed’s web based software) is easier to use and can be accessed from any computer. Dexcom’s DM3 provides slightly more analysis capability, including graphs annotated with food, insulin and exercise data, but for me this doesn’t make up for the fact that it isn’t web based.
Conclusion
Both devices are good, but I prefer the Guardian (I’m now using the Minimed 722 w/CGMS) over the Dexcom. Minimed has given me better reliability and the sensors aren’t nearly as expensive when you consider that the price difference is simply because of the wear indication.
3 Comments
I have used the Dex for about 18 months. I was a little disappointed until I got the 7+ upgrade. With the 7 you could calibrate the system by adding a finger stick and it could ask again in 10 minutes. With the Plus it will accept anytime recalibrate immediately and not ask again for 12 or so hours. With the plus system it seems to be more trouble free. The sensors last much longer. I usually get 12 to as much as 17 days for each sensor. I have even used out dated sensors and one lasted 18 days. My BG results during these extended periods seem to be as good as they are during the first 7 days. They always lag behind the finger sticks by about 15 minutes and sometimes they are off. Usually a quick calibration and they are back on. The greatest advantage is watching the trends by checking the arrow. Also with my new pump I can maintain tighter control by reacting to the levels as they happen. I’m always aware of possible insulin stacking but my new pump tells me my IOB (insulin on board), which helps a great deal.
I have not yet tried the mini-med’s system but I am within a hair’s breath of switching to it. I have had a HORRIBLE experience with the Dex.com. I test frequently on my one-touch and it will tell me I’m 39 where the Dex com is telling me I’m 89. I have tried to work with DEX people but first they tell me I’m callibrating too often, then they say I’m not callibrating enough. They say they don’t care if I switch to the Medtronics system, which I find to be absolute bulls**t. They stand to loose THOUSANDS and THOUSANDS of dollars if I do. They just say I will be very disappointed with the perfomance of the mini-med. I’m afraid I’ll end up dead if I don’t try something different as after 35 yrs of diabetes I can no longer sense lows. I tend to run low, which is why I invested my child’s college education fund to get the Dex.com. Honestly, how much worse can mini-med be? Anyone tried them both. Plus, I JUST GOT (about 5 mo ago) my system so if they have a better one, why didn’t they sell me that one or at least offer to switch me to it? GRRRRRR!!!!
Mary,
If when you calibrate the system, it tracks your glucose correctly for a range near where you calibrated, then suddenly stops being accurate as your blood glucose moves further from the calibration point, it’s quite possible that calibrating has nothing to do with it.
When I was starting out with both systems, it was always frustrating to me when reps/customer support would try to tell me I wasn’t calibrating properly. You might have better luck with Minimed, but my advice would be to try some alternate sensor insertion sites/techniques. Look on some cgms user groups/online forums and you’ll find lots of tips.