For the past ten days, I was lucky enough to try the Dexcom G7, the long-awaited, hotly-anticipated, brand new continuous glucose monitor (CGM) from Dexcom.
The business’ earlier model, the G6, was the “killer app” of CGMs, a device so user-friendly that it even convinced many people without diabetes that they needed the tech, with such exquisite blood sugar accuracy that the FDA allowed Dexcom to tell users that they didn’t need fingersticks anymore. Dexcom did not rest on its laurels — the G7 is completely redesigned, and is a significant improvement over the old model.
But Dexcom’s biggest competitor, Abbott Laboratories, was busy too. In October 2022, I had the chance to wear a FreeStyle Libre 3, and I called it the best CGM I’d ever tried. How does the Dexcom G7 stand up?
To find out, I wore both CGMS — one on each arm — for ten days. Dexcom kindly provided me with one sensor to try as a journalist. Abbott has previously done the same, though this time I used a Libre 3 sensor that I bought with my own money (I’m a regular user). In each case, my opinions are entirely my own.
Here’s how it went:
If you’re used to the older generation of CGMs, you’ll find that both the Libre 3 and the G7 are impressively small. The G6 was pretty sleek, but I way always aware that it was there, stuck onto my body, and had a habit of bumping it into door frames the and like.
The new G7 is tiny! Dexcom reports that the new device is 60 percent smaller than the G6. Even if nothing else about the technology were improved in any way, that slim profile would be well worth looking forward to.
But the Libre 3 is even smaller than the G7 — it’s about the size of two pennies stacked on top of each other.
The truth is that they are both small enough that I do not notice them at all during my day. They are as light as heck and about as obtrusive as a Band-Aid.
The Libre 3 wins here, but it doesn’t really matter — both CGMs are so small that you will probably forget you’re wearing them.
Surprise — there are no transmitters here.
One of the major advantages of the Libre system used to be the lack of a transmitter. The Libre sensor, the little round device that you stick into your skin, was all-in-one. The Libre 3 preserves this simple design.
By contrast, the Dexcom G6 required you to snap a transmitter out of your old sensor and into your new one. Although there were some advantages to this approach — Dexcom users could hack their G6 transmitter in order to get extra days out of their expensive sensors — the process was cumbersome. You had to deal with two parts, each with a very different working life, and it increased the technical difficulty of the Bluetooth pairing ritual you needed to perform to get each new sensor working.
The G7 is, like the Libre 3, an all-in-one sensor. It is fully disposable. Though the G7 may not be hackable, it is now far easier to switch from an old sensor to a new one.
If there was one obvious sticking point with the previous Freestyle Libre CGM systems, it’s the fact that users didn’t just get their blood sugar numbers automatically beamed to a dedicated receiver or smartphone. They had to manually scan the sensor by holding their device over the sensor for a few moments. In our survey of CGM users, manual scanning was frequently mentioned as a major annoyance with the older generations of Libre CGMs.
This scanning movement is completely unnecessary with the Freestyle Libre 3 — as it was with the G6 and continues to be with the G7.
With either system, your smartphone updates with new blood sugar readings automatically.
There is one significant difference between the two: the Libre 3 will provide new blood glucose readings every minute, whereas the G7 only updates every five minutes.
This is a clear win for the FreeStyle Libre 3.
The Freestyle Libre 3 is rated for 14 days.
The Dexcom G7 is only rated for 10 days (10.5 days, really, when you consider the 12-hour “grace period” for switching over to a new sensor).
Libre’s longer life is a significant advantage — not only does it mean fewer annoying changeovers, but it also reduces the amount of time you spend wearing brand new sensors, which are less accurate.
Dexcom has told Diabetes Daily that it is working hard on extending the sensor life to 14 days. But, for whatever reason, they haven’t been able get there yet.
Application & Start-Up
For both models, sensor application was painless and nearly effortless for me. Each comes with an easy-to-use one-piece applicator. Each is pressed flat against the skin. For older CGM models, it was often a good idea to watch a YouTube video to see exactly how to insert the sensor. But the Libre 3 and G7 are both simple and intuitive.
It was easy to pair each CGM with my smartphone. For each, I downloaded the official app, and followed instructions on the app. With the Libre 3’s, you simply tap your phone against the sensor on your body. The G7 was slightly more complex — you enter (or take a photo of) a code on the box.
The Libre 3 gives you your first glucose measurement in one hour.
The G7 is faster: It’s up and running in only 30 minutes.
I was surprised to see that Dexcom includes and requires you to apply a supplemental adhesive. This step was really simple, but I had to walk over to a mirror and fumble with a donut-shaped sticker to get it properly attached to both the G7 sensor and the surrounding skin. It’s a minor annoyance, and the extra sticker makes the G7 more conspicuous.
The adhesives for both systems performed perfectly for me, staying firmly stuck onto my skin for the entire 10- or 14-day wear length. I didn’t really test it though — it’s not summer, and I wasn’t swimming or sweating.
Adhesive quality is a factor for which your mileage may really vary. Many people with diabetes struggle with CGM and insulin pump adhesives — there’s an entire Facebook group, with over 15,000 members, dedicated to troubleshooting rashes and adhesive allergies from CGMs. The manufacturers have been at pains to reduce the incidence of these annoying and occasionally deal-breaking skin issues. But it’s possible that one system is easier on your skin than another, and that could be enough to make the difference for you.
Each system brings a similar suite of extra features, including:
Glucose trend arrows
Remote monitoring for family members/caregivers
Data sharing with healthcare professionals
Data analysis in the smartphone app
Though I didn’t use all of these features, I didn’t find a big difference between the two systems. Each app is attractive and intuitive.
Both CGMs are absolutely good enough to use for diabetes management.
Throughout the 10-days I tested my two CGMs against each other and against my glucose meter. All three were consistently in the same ballpark. I felt completely confident using my blood sugar measurements to guide my eating and insulin dosing decisions. I had no need for fingersticks.
Did one system perform better than the other? Not really. It is possible that the G7 — despite the fact that it only updates every five minutes, rather than every one minute — was quicker to identify blood sugar trends. It seemed to award upward and downward arrows before the Libre 3 would during time when I new, from food or exercise, that my blood sugar was about to change rapidly. But it’s impossible for me to say if this is a real advantage for the G7 or just a fluke during a single small experiment.
As I write this line, my Libre 3 believes that I have a blood sugar level of 95 mg/dL. The G7 says 98 mg/dL. Such tight agreement was very typical, and neither was consistently lower than the other. After 10 days, each app reports exactly the same average blood sugar level: 105 mg/dL.
The G7 can be calibrated using a reading from a blood sugar meter. The Libre 3 cannot be calibrated. I never felt the need to calibrate, either way.
Both Abbott and Dexcom claim to have created the world’s most accurate CGM. As far as I’m concerned, they’re both plenty accurate.
There were two exceptions to their general consistency:
CGM sensors are known to be less accurate during the first 24-48 hours.
In fact, many people with diabetes have learned to more or less ignore their CGMs during that first day or two.
To be perfectly honest, my G7 was a nightmare during the first day of use. It repeatedly bombarded me with very loud erroneous low blood sugar alarms. I turned off as many optional alarms as possible, but eventually I had to bury my phone under a pile of pillows and blankets.
The Libre 3, on the other hand, gave me perfect measurements instantly. But I’ve used it long enough to know that the Libre 3 is not perfect every time. In fact, the very first time I used it, it had the same problem as the G7, sounding false low alarms in the middle of the night. I have no reason to suspect that either the G7 or the Libre 3 performs better than the other during the first day or two.
And after that first day, neither device gave me a single false alarm.
CGM sensors are slower than old-school glucose meters.
A CGM sensor doesn’t actually sample your blood — it samples the interstitial fluid that surrounds the body’s cells. Interstitial fluid carries nutrients from the blood capillaries, including glucose, which makes it a fairly reliable indication of blood sugar levels.
It takes a little while for the glucose in your blood capillaries to filter into the interstitial fluid. When your CGM gives you a new glucose measurement, it’s really showing you what your blood glucose level was about 10 minutes ago.
This 10-minute gap was plain to see as I tested my blood sugar repeatedly after a enjoying a particularly challenging meal. My old-school meter registered the glucose spike faster than either CGM did. But this doesn’t matter much — I would rather have a CGM give me continuous slow measurements than have to use fingersticks again and again after I ate.
This was the surprise factor that really made a difference to me.
The Libre 3 has a Bluetooth range of 33 feet, compared to the G7’s 20 feet. This made a massive difference for me. I don’t have a large house, but when I left my phone in one room and went to another, I frequently found that the Dexcom app lost contact with its sensor, while the Libre 3 kept churning out glucose readings. Given that it would often take the Dexcom several minutes to get back online, the Libre 3 ended up being significantly more reliable.
Given the vagaries and complexities of healthcare economics, it’s impossible to say which CGM system would cost you more.
For those of us lucky enough to have generous health insurance policies (or live in countries with robust socialized healthcare systems), these vital devices could be practically free. For some of us, they may be out of reach.
As of this writing, a month of Dexcom G7 sensors costs $378 at Amazon’s online pharmacy, with an “estimated” cost of $60 after insurance.
In contrast, a similar supply of FreeStyle Libre 3 sensors costs a mere $132 — but the estimated cost after insurance is $75.
But we can say that the Freestyle Libre products usually cost less than the competing Dexcom products. That’s been true for years, though the specifics of your insurance situation will ultimately determine your cost.
Neither of the new CGM systems is ready for use with an insulin pump in an automated insulin dosing (“closed-loop”) system.
That will change.
Dexcom and Abbott are currently racing to get closed-loop integration going as quickly as possible.
Dexcom seems as if it may have a head start — its G6 can already integrate with the insulin pump and dosing algorithms from Tandem and Omnipod. But Abbott, which has been slower to secure similar relationships, recently announced that it had received FDA clearance for use with automated insulin delivery.
If closed-loop pumping is your priority, you’ll have to wait and see.
All things considered, I preferred the FreeStyle Libre 3. It’s slightly smaller, it lasts longer, and I really appreciated the larger operating range. It is possible that the Dexcom G7 is a little bit better at responding to blood sugar changes, but the difference (if it’s real) is subtle.
But really, these are both outstanding products, and each is lightyears ahead of the technology that was available only one year ago. You’ll be happy with either one. Go with whichever model your insurance prefers.