Sensor Vs. Sensor

by Gary Scheiner MS, CDE

As a kid, I loved reading MAD magazine.  It was sarcastic, critical, and held no prisoners.  The “Spy vs. Spy” segment was a personal favorite because of its poignant portrayal of the idiocy of war.
In the diabetes industry, the “war” has traditionally been “meter vs. meter” or “pump vs. pump.”  Today, a major side-battle is brewing between the CGM companies, namely Dexcom and Medtronic.  As insurance coverage and patient/provider acceptance of continuous glucose monitoring grows at an exponential rate, more companies are sure to enter the market.  Abbott’s Navigator system still has a small foothold in some parts of the world, but for now, Dexcom and Medtronic are the sole super CGM powers.  So how do they compare?

For the past 8 weeks, I put each company’s latest system, the Dexcom G4 and Medtronic 530G with Enlite, to a head-to-head test.  Other than wearing the sensors longer than the “approved” number of days, I pretty much followed all of the rules and recommendations that each company provides to users.  Simultaneous calibrations were performed three or four times daily prior to meals, when glucose levels were in a relatively steady state.  The sensors were stored properly and placed in appropriate/adjacent sites, and the sites were rotated consistently.   Extra adhesive was applied over the sensors at the first sign of loosening.  Transmitters and receivers were charged as needed.

Here’s what I found:

Sensor Insertion & Comfort:
Both systems now use very thin introducer needles and automated insertion devices.  Enlite inserts at a 90-degree angle and is much easier to insert and more comfortable than Medtronic’s previous Sof-Sensors.
Edge:  EVEN

Sensor Longevity:
With a little ingenuity (and a lot of tape), both sensors can work well past their initial life-cycle.  Based on my personal experience and that of my clients, I have found that the Enlite sensors last an average of 8-10 days; G4 lasts an average of 12-14.

Alert Settings:
Both systems offer high & low alerts as well as rate of change alerts, albeit Medtronic’s rate of change alerts are much more customizable.  Only Medtronic offers predictive alerts and allows the user to vary settings by time of day.  Medtronic’s latest system also has a “low suspend” feature that automatically stops the pump’s basal insulin delivery when the glucose falls below a specified threshold – an annoyance during most garden-variety lows, but a potential life saver for those susceptible to severe hypoglycemia without symptoms.

Alert Volume:
Both systems can beep and/or vibrate to alert the user of a potential problem and both have adjustable settings, but Dexcom’s vibrate mechanism is considerably stronger, and it can beep much louder (when desired).

Medtronic’s radio transmitter contains a memory chip that stores up to 40 minutes of data and submits it to the receiver in case the receiver was out of range of the transmission.  Which is needed:  the signal only travels a few feet (and is frequently lost even when in close proximity), and it must be removed from the sensor and charged at least every six days.  Dexcom’s transmitter never requires charging and sends a signal that reaches across a sports field or multiple rooms of a house.

For those who use a Medtronic insulin pump, the convenience of having the CGM display right on the pump itself is tremendous.  However, some people (parents, caregivers) prefer to have a receiver/display that can be carried separately or placed away from the sensor.  Dexcom’s full-color, high-contrast screen is simply superior to the Medtronic LCD screen.
Edge:  EVEN

Dexcom’s download software has some nice features, such as the ability to segment data by day of the week and customize analysis dates.  However, it does not work on Mac systems or integrate with data from any pumps or meters (unless you happen to live in certain European countries).  Medtronic’s Carelink software is web-based, works on virtually all operating systems, is easy to use and share, integrates sensor data with pump & meter data, and generates reports that do a super job of revealing post-meal-bolus patterns.

There’s something to be said for a system doesn’t take a lot of work in order to function well.  Other than having a sensor insertion device that takes some dexterity, Dexcom is the epitome of simplicity.  The transmitter requires no charging (Medtronic’s transmitter must be charged every six days).  Calibrations may be performed at virtually any time (Medtronic’s must be done according to a schedule).  Dexcom hones its data towards calibration entries (Medtronic generates error messages when data is off).  Dexcom’s setup and sensor startup startup process is streamlined.  Out-of-range signals are much rarer with Dexcom and don’t require extra steps to re-initialize.

Here’s the biggie.  Most people are willing to put up with some minor inconveniences if the system generates reliable data on a consistent basis.  Medtronic’s original sensor, the “Sof-Sensor,” was infamous for its accuracy and dependability problems.  I saw this with my own system as well as with many of my clients who used it.  So I went into my personal trial with the 530G with Enlite without any big expectations.  And I was pleasantly surprised.  Enlite performed admirably.  There were far fewer lost signals and data gaps.  It wasn’t as “cranky” at the start-up.  And the data closely matched the fingerstick calibrations more often than not.  But it still wasn’t quite up to par with Dexcom’s accuracy.  

Accuracy is best measured by looking at MARD – Mean Absolute Relative Difference.  This represents the difference between fingerstick calibrations and sensor glucose values, so a lower MARD is better.  A calibration reading of 150 mg/dl and a sensor value of 120 mg/dl represents a MARD of 20%.  The overall MARD for each system was as follows:

Medtronic Enlite: 18.66%  MARD
Dexcom G4:  12.60%  MARD

Keep in mind that this data (particularly the Medtronic MARD) differs from data published by the companies from their own pre-market trials.  I’d like to think that I put the sensors through the rigors of a serious real-world test:  changes in sleep patterns, travel, lots of unusual foods, extreme exercise conditions, stressful situations, and so on.  In other words, the rigors of my normal life.

In terms of which system was more accurate more often, Dexcom had a definite advantage:  Dexcom G4 was more accurate than Medtronic Enlite 67% of the time; Medtronic was more accurate 27% of the time, and the two showed equal accuracy 6% of the time.

Neither system was particularly accurate during the first 24 hours after sensor insertion, with MARDs in the 20-25% range.  But things improved considerably after “day 1” and continued to improve over the life of the sensors.  Both systems also tended to underestimate glucose levels more often than overestimating (Dexcom moreso than Medtronic)… which is good for those trying their best to avoid hypoglycemia, but not ideal for those who are easily annoyed by false low alerts.

Percent of Readings
BELOW Calibration
Percent of Readings
ABOVE Calibration
Exact Matches
with Calibration







So there you have it.  Do with it what you will.  Both companies (as well as Abbott, from what I hear) are aggressively developing their next generation systems, so this may all be obsolete soon anyway.  But for now, I hope it gives you what you need to make an educated decision.  Whatever you choose, you’ll be far better off than not using CGM at all!

By |2016-12-08T23:27:01+00:00January 31st, 2014|Thinking Like A Pancreas Blog|27 Comments

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  1. Sarah February 7, 2014 at 2:32 pm - Reply

    Thank you so much for this review, Gary. I’ve been watching your photos on the Facebook page, so I was hoping you would write a post about your experience. Definitely sharing! 🙂

  2. Bert February 7, 2014 at 3:19 pm - Reply

    CGM sensors are all well & good, but until the cost for 1 years worth of sensors drops below the cost of 2 large screen TV’s, the technology will not get adopted.

  3. Sandy Zellmer February 7, 2014 at 4:01 pm - Reply

    We get 11-12 days out of our Enlites and within 10% accuracy. Love them! 🙂

    • Carol February 7, 2014 at 5:36 pm - Reply

      Sandy we are getting that kind of accuracy too. I have not went beyond the 7 days yet because of having to remove transmitter to charge. We have had 3 low suspends (ours set to 65) and they were spot on.

      • Sandy Zellmer February 7, 2014 at 6:46 pm - Reply

        That’s great Carol! We have had our low suspend go off on us a couple times and it was right on also. It’s great having that feature.

  4. Nancy Hill February 7, 2014 at 6:20 pm - Reply

    A rental system would be good.
    If a GP’s surgery held one or two that could be borrowed for say a fortnight one could learn a lot especially soon after diagnosis.

  5. Tory February 7, 2014 at 6:45 pm - Reply

    Thank you for a such an informative post. As a pumper for over 8 years, and pumping with Medtronic for 4 of those years, I would add that while Medtronic claims to have web based software that works with any operating systems, there are a number of times when Medtronic has had system failures and required Mac users to upgrade systems which really shouldn’t have to be a choice by users or phases out/in technology without leaving a way for users of older technology to upload.

  6. Misty February 7, 2014 at 8:02 pm - Reply

    I really appreciate your review on both of these systems. We find the information from our daughter’s cgm to be invaluable.

  7. Doreen February 11, 2014 at 6:31 pm - Reply

    Gary, thank you so much for performing this test and sharing your observations. I recently switched from Dexcom to the Medtronic Enlite. I love the low threshold feature of the Medtronic, it gives me such peace of mind, but it’s much fussier to deal with than the Dexcom system. I’m sure with time that I’ll adapt to the different features of the Enlite and it won’t feel so different anymore.

  8. John February 13, 2014 at 11:09 pm - Reply

    Just want to chime in with a THANKS for such an in-depth review and evaluation of these CGM’s. Very helpful and informative.

  9. Vicki February 16, 2014 at 4:44 pm - Reply

    Thanks Gary. Would prefer to hear from a real time user vs. a study.

  10. Mike February 21, 2014 at 7:30 pm - Reply

    Very helpful article — Spy Vs Spy. Nice lead in. Question: I switched from Dexcom 7 to 4 ( platinum); I hear and read people saying that sensors last more than 7 days. However, my DC 4 automatically cuts off and stop showing any BG readings at 7 days. Is there a way to wear it longer? Am I just missing something? Thanks.

    • Leah November 17, 2014 at 3:01 am - Reply

      All you have to do is tell the receiver to stop the sensor at some point during the 7th day of wear. Then you can immediately tell it to start again. It will go through calibrating again, but ultimately you will never remove or change the sensor or transmitter. Just leave it as is. The receiver doesn’t know that you didn’t change to new area. You can keep doing this as long as you are getting accurate readings. Mine last over 14 days and by then it’s taking so much tape I’ve decided to switch. A few did fail after 12 days but I’ve worn it for 18 days without issue.

  11. Alex Lind February 26, 2014 at 7:10 am - Reply

    The comment about Medtronic software and Mac is false. It simply doesn’t work. It requires Lion and out-of-date Safari plus installing Java. Once you upgrade to Mountain Lion or Maverick’s Carelink ceases to function. And their support line is beyond useless if you have a Mac, they simply aren’t trained for it. The lack of quality in their software is why I will be switching to another pump manufacturer when this one is done.

  12. Toby February 26, 2014 at 1:43 pm - Reply

    We, too, just did a side-by-side comparison with our 11 yr-old son. Our results matched your results in nearly every category. I think both are awesome systems. In the end, we decided to go with the DEXCOM because we can more easily monitor our son over night (we set in on a baby monitor to hear go off) and we can monitor him during sport while he is on the field.

  13. Colby Cook February 27, 2014 at 8:28 pm - Reply

    I’m a diabetic for 26 years on and off the meditronic 723. One thing that is not mentioned is Price which is the #1 reason i chose the dexcom along with accuracy. I felt I could live with the inconviance of carring two devices… No much on top of that mattered to me. Although with extra adhisive find myself leaving my dexcom site in for 1 month at a time ( no infections yet 🙂 and only find the longer left in the better accuracy i get. My a1cs are 2 points lower since Aug 2013 when I began dexcom and I havent had a low of any sinifance… It has been very nice. Plus feom time to time ill let my daughter and son (type1 d) try it out. Looking forward to now the fda has approved for kids to getting them one. The key really is awarnes and it really is on my mind every five min i know where im at. My sister uses RTM from minimed and swears by it as well. Comes down to cost … Questions I can be found @diabeatitnow

  14. Monique March 5, 2014 at 1:58 pm - Reply

    A friend’s insurance company won’t pay for a pump. They claim that they paid for one in the pass year, however, she doesn’t have one. Now her Endo is battling with the insurance company. How should she handle this matter?

    I suggested asking the insurance company to give her the name of the pump and company that delivered it. Then call the company and ask if they have a pump under her name. Last, ask for written documentation to deliver to insurance company about this that she didn’t receive.

  15. Nell April 6, 2014 at 6:44 pm - Reply

    I loved my Dex4, but just went on Medicare and it pays NOTHING for CGMs, or sensors. 🙁

    • Karren Meggitt August 6, 2014 at 11:03 pm - Reply

      Do you have a Medical Ins. that will cover it? If so, what is it. We are thinking about moving and will lose my Ins. that I now have and am not finding any Ins. that will cover it. I also have Medicare, and no help there. It is so expensive I wont be able to pay for it. Any info will be appreciated. Thanks Karren

  16. Ramona August 7, 2014 at 4:31 pm - Reply

    Thank you so much for testing out the sensors and posting your observations! I am trying to decide between the two, and I was thrilled to find this article. Exactly what I was looking for. It was a great idea to test the sensors simultaneously and let the community know what you think in such a clear and concise way. Thanks!

  17. Ashley September 8, 2014 at 12:14 am - Reply

    I have been pumping for 4.5 years and am in the process of purchasing a new pump. Debating between the Medtronic Veo and Animas Vibe (having Dexcom G4 integrated system in Canada)…Medtronics transmitter needs to be recharged every 6 days…Animas’ never needs charging, which brings me to the question of how often will you have to replace the transmitter (I believe that the warranty on the Vibe/Dexcom system is only 6 months)…does anyone know or have experience with the Animas Vibe with integrated Dexcom G4 system in this regard?

    • Bernie October 12, 2014 at 11:06 pm - Reply

      I have the Dexcom G4 and LOVE IT! The accuracy is amazing. I keep a sensor in for 14 days(2 cycles). While the company states that the transmitter only is under warranty for 6 months, they last around 12 months.

  18. Aileen November 22, 2014 at 1:38 am - Reply

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  19. Joe McGraw January 11, 2015 at 4:55 pm - Reply

    I am trying to get a handle on the cost of each. Are they covered by Medicare? Out of pocket cost? Thanks.

  20. Lis Warren January 19, 2017 at 11:00 pm - Reply

    I’m currently trialling the new Guardian Connect stand alone Medtronic CGM (transmits to iPhone) in the U.K. alongside my Dexcom G4 ( transmits to Animas Vibe). Only had it a few days but am liking it and it’s far more accurate than I’d anticipated given older Medtronic incarnations. Will feed back in 3 weeks when the trial ends..

  21. Tom August 28, 2017 at 9:53 am - Reply

    Would love to see an update with the latest from these two CGM competitors, the G5 vs. the Medtronic Enlite & 670G? Does Medtronic make a pure CGM? I understand that Medtronic now has its closed loop CGM/Pump system, but does it have a pure CGM play?

    • alicia downs October 16, 2017 at 7:13 pm - Reply

      Yes, Medtronic does have a CGM alone system. It is typically used by doctors practices for trial monitoring.

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