I have been using continuous blood glucose monitors for the past five or six years, and it has been a godsend, compared to pricking my fingers or forearm several times a day to check my blood sugar levels. Up until a year and a half ago, I was using the Freestyle Libre 2 fourteen-day sensors, which required a physical tap from a dedicated reader or a smart phone with an app to take a reading. More recently, I'd upgraded to the Freestyle Libre 3, which automatically sends readings to my phone via Bluetooth, which is even more convenient. But all that came to sudden and unexpected end this past spring.
My health insurance changed their formulary, and now only covers Dexcom sensors, but rather than just smoothly switch me over to their preferred brand, there ensued a two-month fight with said insurance company to even get those. I honestly believe their goal was to try and frustrate me back into pricking my fingers all the time, but thankfully, I was stubborn enough to prevail.
I finally got my hands on a supply of Dexcom G7 (DG7) sensors three days ago, and put on the first one today, where it is running alongside my next-to-last Freestyle Libre 3 (FL3) sensor for its final couple of hours. I did this to be able to compare readings with the two, and they seem to be spot on, within a few points of each other. But how do they compare in other ways?
I suppose the best place to start is the steps to put the sensor on and activate it. The FL3 is pretty simple and straightforward. Clean the area on the back of the arm where it will be applied, open the applicator and press it into the skin. The spring-loaded applicator then attaches the sensor, which is about the size of a nickel, to the skin. The sensor then must be activated by tapping it with a smart phone, on which the Freestyle Libre app is active. An hour later, the phone starts receiving readings every minute.
By comparison, the DG7, which is noticeably larger and thicker, closer in size to the Freestyle Libre 2, is also a bit more complicated. It uses a similar spring-loaded applicator, but it's a little more complicated to use, in that one must press it into the skin to retract a safety collar, which enables a trigger button on the side of the applicator. The sensor is put in place by pressing the trigger button. This is a more cumbersome process, which subsequently requires the user to press the sensor firmly into place for a few seconds and then rub a finger around the periphery of the sensor a few times to ensure firm attachment.
If this makes one suspect the DG7's adhesive isn't as good as that of the FL3, one would be correct in that assessment, because the next step is to apply a provided over-patch. Such patches are optionally available for the Freestyle Libre sensors, but are not included in the package. I have a supply of them on hand, but have only used them when I'm planning to go swimming, particularly in salt water, or when the sensor has been knocked loose or the adhesive is otherwise failing, but the sensor is still functioning. By comparison, the over-patch is required for the DG7. Both sensors can be used when showering or swimming, but the DG7 is good to a depth of eight feet, versus the FL3's three-foot maximum depth.
Activation of the DG7 happens a little differently than with the FL3. The 30-minute warm-up period, as opposed to an hour for the FL3, begins automatically once the sensor is applied, but it must still be paired with one's phone, either by entering a four-digit code in the app or scanning a QR code, both of which are found on the side of the applicator. By the time I had applied the sensor and over-patch, and then paired it with my phone, the sensor was already a couple of minutes into the warm-up period. It should be noted that until the DG7 sensor is paired with one's phone, no readings will be received, but the timer will be ticking on the sensor's 10-day functional lifespan.
Yes, the DG7 sensors do not last as long as the FL3, just 10.5 days, including a 12-hour 'grace period', as compared to the FL3's 14 days. Realistically, this means one will go through three sensors a month with the DG7, as opposed to two with the FL3. Another functional difference is that the DG7 sensor transmits data to the phone app once every five minutes, instead of once a minute for the Freestyle Libre sensors, which means it's capturing only 20 percent as much data. Until I've lived with the DG7 sensor for a while, I won't be able to know know how much of a difference this makes. I'm suspecting it will be relatively little, as I will still be able to see trends in the app, despite having fewer data points. The flip side of this coin is the DG7's impact on my four-year-old iPhone's battery life. If the sensor is only transmitting data twelve times an hour instead of sixty, I could see a potential for improved battery life. Time will tell on that one.
Other notable differences between the sensors is that the DG7 must be within 20 feet of one's phone, versus 30 feet for the FL3, but because the DG7 transmits data only once every five minutes, one has greater latitude to stray away from the phone and move back into range. Also, the DG7 offers greater flexibility of approved locations on which to affix it--back of the upper arm or abdomen for adults, as well as upper buttocks for small children, while the Freestyle Libre sensors are approved only for the back of the upper arm.
Having only had the DG7 sensor on my arm for a couple of hours, I have not yet been able to form an opinion about whether I like it better or worse than the FL3, and I accept that human nature being what it is, I would naturally lean toward the tried and true, especially since I was forced to make the switch when I was quite content with the FL3. Expect an update in ten days or so, after this DG7 sensor expires and I put on my final FL3.
UPDATE, two days later--After wearing the DG7 sensor for two days, I'm getting used to it, but I do find it less comfortable than the FL3, both because of its size and the over patch. The phone app is comparable to that of the FL3. The feature set seems to be much the same, but due to the less frequent data points, it is shown as a series of dots, instead of a continuous line with the FL3 app. Sharp and sudden increases or decreases can appear to be data gaps to the untrained eye.
Additionally, DG7 sensors will also send data to a smart watch, without a
phone, a feature not available with the Freestyle sensors. I'm not sure
whether this will entice me to take the plunge for an Apple Watch, but
it does give me another reason to consider purchasing one. The larger question is whether that one reason outweighs the other various reasons I have found not to take the plunge.
I also feel that my preliminary supposition regarding phone battery life is proving to be correct, but not dramatic. Using the FL3 sensor, my phone's battery would be down to between 20 and 40 percent by the end of the day; whereas, yesterday it was at 58 percent when I went to bed. It is now mid-afternoon, and with fairly typical phone use so far today, the battery is at 83 percent, compared with 60-70 percent when using the FL3 sensor and app. I fully realize that I have not yet amassed nearly enough data to fully support or refute my hypothesis, but I feel like it is promising.
Day 10 UPDATE--So, I just changed out my first DG7 sensor a little while ago. My thought last night was to use the last of my FL3 sensors and run the two simultaneously to collect a few hours of comparative data before the DG7 sensor ran out. It turned out my last FL3 sensor was defective. I was awoken from a sound sleep just before 4:00 a.m. by a low glucose alarm that turned out to be erroneous. The FL3 sensor was showing my level in the low 50s, while the DG7 was showing it in the low 100s. The fact that I was feeling absolutely no symptoms of hypoglycemia told me the DG7 was providing more accurate information. I was kept awake by a series of false low alarms over the next couple of hours before receiving a signal loss alarm. The phone was no longer receiving data from the FL3 sensor. Finally, about three hours later, the FL3 app flashed a message on my phone screen, instructing me to replace the sensor, which I did once the DG7 sensor ran out. By that time, I had torn the defective FL3 sensor off of my arm and deleted its app from my phone. Out with a whimper, I'd say.
Normally at this point, I'd be on the phone with Abbot Labs, manufacturer of the FL3 sensor, requesting a replacement, as I have done many times before when they have failed prematurely. But this time, I just took it as a sign that it was time to fully make the switch over to the Dexcom sensors.
After using one for a full ten days, I've decided that although the FL3 is the hands down winner for comfort and convenience, especially when it comes to applying and activating the sensor, there are also things that offset the inconvenience. I am seriously considering buying an Apple Watch to take advantage of its ability to receive data from the DG7 sensor.
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