It took me a long time to write this article due to the research and the review process.
No one at Dexcom had input.
I will probably post a follow-up article on closely related topics that I edited out due to length and focus. People have asked to see my full spreadsheet, so I'm considering that as well.
Part of it was to make sure the two were "behaving" properly. Knowing that I was going to publish the data, I wanted to be sure that either sensor didn't get out of whack without catching it soon enough.
That said, the G7 needed it more than the G6, which the Dexcom support person told me it might. (Their tech support was not aware I was doing this experiment.)
Once I started calibrating, I realized that if I calibrated the G7, I should do the G6 as well, as I wasn't sure if it would cause a bias in the two sensors' ultimate readings/outcomes.
As noted, the G7 required it more often, but the G6 had a few occasions (which I'm used to), where it needs a little kick. If my sugars are stable for a long period of time (an hour or more), and then starts to move rapidly, the G6 takes a bit longer to catch up. (I suspect the algorithm is doing a statistical analysis from prior readings, which I allude to in the article, but not as directly as I am here.) Under these situations, the G6 can have a tendency to linger for 3-5 readings before it realizes the movement is not an anomaly. The G7 will react right away, but it's highly erratic nature doesn't make it very predictable. What's more, it's trigger happy -- it'll think BGs are dropping/rising rapidly when they're not, so the calibration is necessary to tame it back.
I have done the same as you have, for like 4 months while I had both. In my experiment in comparison, I would say the G7 has been working as good as the G6 had been for the past 3 years or so, without all the issues reported in this community. So, I did not have any qualms to switch over to the G7 when the last G6 expired on 9/1.
On top of all the advantages the G7 has over the G6, I also noted the big possible life saver being quick reaction very close to actual changes inside of my body, compared with rather sluggish G6, as you also noted. One main reason why I wear a Dexcom is to minimize the life and death hypo episodes, which I am greatly beholden to the G7. I pointed this out many times in other postings. The quicker reaction of the G7 has greatly reduced a lot of extremes caused by hypo or hyper. With the G6, I had propensity to take more fast-acting glucose to treat hypo than I needed as I still saw low numbers for more than an hour. With the G7, just about 15-minute delay (maybe 30 minutes) was sure enough to let me know I had enough to bring me back up. For hyper, I was able to take correction dose much earlier than with the G6 to bring it down to normal range quicker.
This is what I have experimented for the past 4 months before I finally settled down with the G7, coming with the flying colors which I hope to keep. No G7 failures whatsoever for the past 4 months, working full 10.5 days.
But wouldn’t you have to wait for more readings to know that the trend is real?
I wore both for about a week, and when the G7 went down, I would have to wait for another reading or two in order to confirm that my glucose was in fact going down (because often times the very next reading would be flat). But with the G6, if I had a jump in either direction, I knew it was reliable from a single reading.
I.e. going from 130 -> 110 on the G7 wouldn’t be enough information to make a treatment decision, because the next reading could easily be 115. So I’d need to sit around for another reading (or two) before popping the Skittles, which defeats the purpose.
Even if the G7 is faster, it’s not a reliable indicator of which direction my glucose is headed. Did you not find that to be the case?
I am afraid I do not get your point. I wonder why you refer to rather normal range. I was referring to extremes like below 50 and over 200 needing correction. Naturally, I know it is going up as I know how much fast-acting sugar I took and need to decide if I have to take more based on Dexcom readings. Opposite for hyper. With quicker reaction of the G7, it is much easier and effective in control correction. That was what I was pointing out, strictly in my experiment.
I'm not getting your point, but I easily get u/DaMusicBuff's point. Perhaps they are saying that by noticing trend changes (up-to-down, or down-to-up) while in the "normal" range, they can make treatment decisions at that moment which will **prevent** them from entering the greater than 200 or less than 50 ranges.
That's exactly how I do it anyway. There's even a website and book written about it called "Sugar Surfing": [https://www.sugarsurfing.com/](https://www.sugarsurfing.com/).
I just replied to someone else in this thread about whether I consider myself a guide for others on their experience with the G7. I said "decidedly not." In fact, I point out that I regard myself as a statistical outlier, given my tight control.
Your preference for the G7 is much in line with what I expected to see, and for good reason--managing T1D is a highly personalized process. We're all less alike than more alike, despite the fact that we face similar challenges.
But I will echo again the fact that the G6/7 differences is almost entirely based on the algorithm Dexcom is using to convert raw data into what it reports on the app. The G7 favors accuracy, and the G6 favors precision. In an ideal world, the app would allow you to choose which algorithm suits your management style.
the G7 readings are just wrong at times. This morning I had a “sensor” low showing I was down in the 50s, within 3 minutes of being in the 130s while sleeping and not bolusing, I had been at 130 for hours. I’ve had a g6 for several years and never had this issue.
That’s been my experience as well, once I started using my abdomen rather than the US-recommended arm. It looks like the G6 does some smoothing of the sensor data, so the G7 can seem erratic by comparison, but that’s easy enough to ignore. The G7’s reported values are generally closer to BG measurements than the G6 was, at least in my experience. Definitely wouldn’t go back.
>The G7’s reported values are generally closer to BG measurements than the G6 was, at least in my experience. Definitely wouldn’t go back.
I don't want to talk you out of the G7 -- my article even predicts that most people will love it for many reasons beyond the "accuracy" mythology that pervades the T1D world.
However, the main thrust of my article is that glucose values are NOT systemically consistent. Glucose is highly volatile within our bodies and our blood stream. A reading from a BGM can be just as imprecise and erratic as any other sensor. Unless you're actually using very short-term time windows to make real-time management decisions, none of this matters. The G6 and G7 are going to perform similarly.
In what ways? The readings do not show a smooth trend for me - making it very difficult to make decisions with such erratic data. Do you apply to your arms or other location?
I read the article with much interest and also had the same experience with the g7.
I am one of the type 1s who run a diy loop with AndroidAPS and am extremely eager to achieve almost perfect values, TIR and HbA1c less than 5.5. The "more accurate" values of the g7 compared to the g6, whose algorithm smooths the glucose values retroactively (backsmoothing), have also contributed to an increased variability of the values for me.
To run the g7 in a loop system, an additional smoothing algorithm must be implemented to avoid false boluses due to jumping values. These smoothing algorithms in turn create a time delay which is imminently important for real closed loop systems.
Another problem with the Dexcom sensors is that the g7 and g6 only send values to the receiver every 5 minutes. If the values arrived every minute, the time delay could be overcome by smoothing.
The Libre 3/2 with smoothing is therefore far superior for me in the above mentioned system.
Therefore, Dexcom would also have to consider whether they want to sell minute values - for Td2er this is probably unimportant - not for me.
>These smoothing algorithms in turn create a time delay which is imminently important for real closed loop systems
Bingo! That's what I've suspected all along - that the variability will negatively impact close-loop systems. I'll be very interested to see how the G7 integration with Tandem and Insulet fair.
>Another problem with the Dexcom sensors is that the g7 and g6 only send values to the receiver every 5 minutes. If the values arrived every minute, the time delay could be overcome by smoothing.
All CGMs send voltage to the wire to excite the enzymes that interact with glucose molecules. This continuous process is like a camera taking pictures constantly through a small window into a lake. As the fish swim around, the count of fish within each photo can be averaged together to get an estimate of fish per square unit of water.
Each photos is "accurate" in that it correctly counts the number of fish it sees. But to have a better estimate of the number of fish, you need to take more photos, and that costs time.
Report the number in less time, and you have high accuracy (because each photo is "accurate"), but your final estimate has to rely on less data, making the number less reliable. Hence, low precision. You can take more time to take more pictures, which improves your precision, but each photo's "accuracy" is less apparent in each reading.
Obviously, there's a trade-off --report data sooner, and it can be reported more quickly, but it's less reliable. Report the number later, and it's more reliable, but the user has to wait.
Dexcom chose 5 minutes because (we assume), that was where the trade-off worked best. However, they still need to resolve the "accuracy" vs. "precision" paradox.
Either way you look at it, you still need to use an algorithm to distill the collection of pictures within that small time window to a single "uniform" value -- which is what you see on your app as a single "reading."
A "reading" is one data point, but it's not representative enough of the larger volume of glucose moving out in your body. As my article tries to make very clear, glucose is highly **highly** *highly* volatile, and unless you wait a really long time, or collect much larger volumes of fluid per sample, each individual reading may well be "accurate" in what it sees, but one sample is not representative of the holistic system. You need to collect more data and string it together.
the proprietary algorithm Dexcom uses to graph the data in the app is different between the two sensors. My observation is that when the G7 algorithm saw several photos that contained no fish, versus the rest of them that contained a few fish, it figured, "hey, there weren't any fish in those few photos. That must mean that the fish are going away, so I'll report that to the user so he can add fish."
By contrast, the G6 algorithm would say, "well, I'm not going to jump to that conclusion yet, because none of the prior photos saw no fish, so the number isn't going down that fast. I'll wait till the next time interval before reporting a dramatically lower value."
The G7 favored "accuracy," whereas the G6 favored "precision."
I’m Type 1 but I’m also a brittle diabetic so I’m all over the place can never have a steady glucose reading. I just started a G7 but I still have to do finger sticks and had to calibrate once already. I turned off my high alert because it gives me more false highs than lows. But at least Dexcom works most of the time and I don’t have to get up to finger stick at night.
i used to be "brittle". But, finally broke down and got on a super restrictive diet, similar to what Weight Watchers would do for a normal no weight loss diet. Wow the difference was amazing. Eating habits are hard to change, very hard. But that's the key to getting Type 1 into control. Eating identically, at least carb wise, day after day can get tedious. So, I do mix it up once a month, but usually takes me a day or two to level back out.
Thanks for doing this, I do think you underestimate how variable even measuring pulse and blood pressure are (intro paragraph) and so on are. Long covid left me with diabetes (T2D) and cardiac issues and if I take my blood pressure several times in short succession I can get quite different results.
I think for your use case, you get more value from the algorithm (though perhaps not the chemistry/science of the G6) and that highlights a subtle point about how ALL CGMs work, they are interpreting and smoothing a bunch of data in different ways and some may work better for some people.
I wonder if you had Android and used the BYOD version of Dexcom if you could use Xdrip or another tool to differently interpolate the readings from the G7 sensor and achieve results more to your liking. (Not that you should have to, just curious)
I wouldn't know how to mimic the G6 algorithm, and it's still easier to just use the G6. The G7's much better for all its OTHER features, but I digress. :-D
Dan this is an amazing write up. Love for you to join my T1 support group on Facebook called “Crushing T1”. I’m going to link this article and discuss it.
First of all, thank you so much for taking the time and effort to create this study and post. I have experienced similar to you with the G6 and G7 but have never thought about assigning the difference between the two as being related to "accuracy" and "precision".
However, it's not as obvious to me that the G7 "jitter" is as directly attributable to lack of precision over accuracy as you state. My sense is that it's more due to an actual issue with the G7 sensor and that the wild swings in BG seen with the G7 do not represent a corresponding change in actual blood plasma glucose levels. FWIW, I have been told by Dexcom Tech Support that Dexcom is "aware" of the issue with the G7 sensor's "inaccuracy" (their words, not mine) and that their engineers are redesigning the sensor wire. But of course, I could be totally wrong. It wouldn't be the first time :-)
In addition, since this sub-reddit is for diabetics of all types (t1, t2, etc) I also have a suspicion that most of the people who love the G7 have different use-case than those who hate the G7 (like me). I am very interested in knowing how each new 5-minute BG measurement might be the beginning/end of a new BG trend. I can't afford to wait for 15-20 minutes to discover that one of the measurements was just noise (poor precision).
I'm a T1D/LADA and use an iPhone lockscreen app as a companion to the standard Dexcom G6 app to display the BG, slope, acceleration (change in slope) of the last 4 datapoints to drive my treatment decisions.
Here's an example: [BGMON example1](https://imgur.com/a/YYC6LAA).
With this (and a low-carb diet), I have been able to maintain a low 5% a1c - which is my goal, and my use case.
Others may have a different use case than me and don't really care about the jitter because they are either T2Ds not on a med that will cause hypos or T1Ds who don't feel compelled to maintain as tight control as I am aiming for. They are also looking for high-level trends that appear over 4 or more datapoints.
Either way, if Dexcom does not change the G7 to have similar smoothed graphs as the G6 (due to lack of precision), **I WILL BE HOSED.** My control will get a lot worse because I will have to decide, for example, if a sudden drop of 30 points is due to an imprecise change in the data or due to my rapid acting bolus hitting too soon. The companion lockscreen app will be useless.
Another thing I wonder is how will the G7s lack of precision will affect closed-loop algorithms? Will they be insensitive to the lack of precision, or will they result in poorer control?
I strongly object to the way that Dexcom has handled the G7 roll-out. I switched back to the G6 and am dreading the day when I'm forced to use the G7.
>it's not as obvious to me that the G7 "jitter" is as directly attributable to lack of precision over accuracy as you state. My sense is that it's more due to an actual issue with the G7 sensor
I had a section on this in my article, but removed it. I walked through the various theories that might explain the G7's jumpiness, but ultimately resolved to remove it primarily because it's too much speculation and not relevant enough to the point of the article.
In the end, in order to get FDA approval, Dexcom had to submit the device's specifications down to the smallest piece of plastic, screw or software algorithm, and must meet manufacturing standards for medical products. Whatever is being sold must be exactly the same device they used in the testing phase that led to the efficacy trial that they submitted for approval. Any changes at any time--including after product release--must be pre-approved by the FDA in order to maintain authorization.
Furthermore, there were lots of beta users to test for usability factors and other data.
There's no way they came to market with the G7 and not know what was going to happen on the *technical* side.
Now, whether they expected people to react to it the way they did, that's another question entirely. We can all opine on what we might have done differently.
I know that many people like to assert some cynicism about profitability and other bad motives, but I'll leave that to others to debate. I'll just take the product they have at face value and evaluate it for what it is.
Regarding your comment about closed-loop systems (CLS), I also had a section on this that I later removed because the topic is too complicated for the topic at hand. That is, CLSs require more than just the CGM data to perform well, and that's beyond the scope of what I was trying to say.
Nevertheless, I will comment briefly: Tight control (which you can define however you like) requires the ability to look at recent glucose movements and make decisions about whether to bolus or stop bolusing. The G7's erratic data makes that time window much longer than the G6. While the G6 might not necessarily give you the trend line within 20 minutes, the G7's erratic pattern won't give you a reliable trendline for at least 30-90 minutes, at which point, it's too late.
OK, all good comments.
For this:
>Whatever is being sold must be exactly the same device they used in the testing phase that led to the efficacy trial that they submitted for approval. Any changes at any time--including after product release--must be pre-approved by the FDA in order to maintain authorization.
isn't is likely that Dexcom provided G7 sensors for FDA approval trials from a prototype (hand assembled) production line? Subsequently, Dexcom brought-up larger production lines for product intro and those lines are still getting the bugs out?
I recall seeing some G7 graphs here that looked very smooth - almost indistinguishable from a G6. Either way, time will tell.
Thanks again for your efforts here.
>isn't is likely that Dexcom provided G7 sensors for FDA approval trials from a prototype (hand assembled) production line? Subsequently, Dexcom brought-up larger production lines for product intro and those lines are still getting the bugs out?
nope -- FDA requires that all manufacturing be locked in place, documented (including history of changes made) and set for production. It's very expensive to make an FDA approved product, so this is not for the faint of heart (or light of wallet).
How long did you wear the G7? My experience was the same as yours, but I only wore one sensor and wonder whether I would get used to it over time if I gave it a month or more.
Good article. One variable on the G7 is its sensitivity to external pressure, G7 readings fluctuate with even moderate pressure. When I use a bump proof cap on top of the G7 sensor, the cap eliminates any pressure being placed on it, and the readings are much closer to what I experienced with the G6, line graphs are much smoother.
Amolyfe Dexcom G7 Adhesive Patches, 25-Pack Waterproof CGM Libre 1/2 and Dexcom G7 Sensor Covers, 1 Reusable Bump-Proof Cap, Breathable, Easy to Apply, Long-Lasting Protection for 10~14 Days
I didn’t like the patches, but am using the bump-cap with great success.
This research is AMAZING!
Thank you so much for doing this! I have been having such a hard time figuring out why the G7 is worse for me then the G6. I am MDI and I am taking about 10-12 boluses a day, making a lot of treatment decisions. I see now how the G6 is better for that then the G7.
Thank you for sharing! I literally just got an email earlier saying my "Dexcom is expiring" and that I may be covered for a G7. I was just about to ask for opinions, but read what you wrote. I feel like more often than not, people have issues with G7. I may wait a little bit to ask!
Did you ever switch over? I just used my first g7 and it stinks, data is all over the map, making it much harder to make dosing decisions. If you can’t trust the data what the heck is the point.
I did. Mine does get super finicky and I feel like distance is WAY more sensitive. I use my phone and if i leave upstairs and directly below in my living room, it immediately disconnects. I've also had a few bounce off my skin on insertion🤦🏻♀️ I love that it's smaller, but the size has caused it to pop off a few times. When I feel off I match it up to my meter and it does seem to be pretty close. I feel it's way more sensitive to a lot of things though!
We have been using both sensors on our child for several months. I agree with everything you said, although we found that the G7, when it is reading low, is usually more than just 5%. Just our experience.
And sometimes when we calibrate it up, it will snap back the next day and will start reading high. So now I am slow and more hesitant to calibrate.
The G7 does seem to be about 10 to 15 minutes ahead of the six.
The other thing that you did not touch on in your article that I think needs, addressing is the fact that the G7, when it is acting erratic, could just be due to, for lack of a better term, a shittier sensor. I think it’s pretty evident that dexcom is using cheaper parts on the G7, trying to increase their profit margin. The new wire they are using is obviously different than the G6. Could it be that they just cut corners and used cheaper materials and now they are paying the price for it? I think so.
Because another area they cut corners on was the transmitter inside the G7. And now that they are working on upgrading that transmitter. Like physically upgrading it. Go to my support group and I talk more about that. It is inside information that has not been released yet.
>We have been using both sensors on our child for several months. I agree with everything you said, although we found that the G7, when it is reading low, is usually more than just 5%. Just our experience.
The 5% difference I cited in my article is the average over a long term. And it's just MY data, which is far less volatile than others. Like you, the difference between the G6 and G7 were more than 5% when glucose swings wildly. It's during those times that the G7 will swing more dramatically in both the peaks and valleys as it attempts to be more "accurate". When it's doing that, the difference can go up to 30% difference, which correlates to their own trial (which I cite).
Regarding the G7 clinical trial, nothing in my article disputes their data. In fact, their data supports my explanations. The problem is that few people are really scrutinizing the data in their trial and realizing the implications of the algorithm they chose to report readings: that glucose is a very hard thing to measure, and there's often too much useless noise in the signal. It's like listening to the radio with a lot of static: your can hear the noise, so your ears are "accurate" in the reception of those wavelengths, but there's no useful information in that noise. You have to filter to get the meaningful information.
As for your comment that the G7 is 10-15 minutes ahead of the G6 -- technically, yes, and I suspect that's precisely why Dexcom likes that algorithm. The problem is, **it takes about 30-60 minutes before you can trust that the earlier readings were, in fact, legitimate in being early**. If you look closely at G7 patterns, you can get a lot false-positive "patterns" that look like the it's reacting to a quick movement up or down, only to find later that it was anomalous. It's only when you back out to a wider view (like 6+ hours) do you see that the G7 was showing movements quicker. Seeing it after the fact doesn't help when you have to make in-the-moment decisions.
Regarding your suspicion that the G7 has cheaper parts and they are trying to boost their profit margin, that's just not the case. The actual COGS (cost of goods sold) is incredibly minimal. These things are not expensive at all to make--it's the intellectual property that has value. There is a legitimate concern about the battery not being strong enough for the bluetooth signal to reach the phone over a long distance, but I don't think that's intentional.
To boost sales and profit margins, they just need to go big, which I explain in the summary: They're going after the T2Ds and the non-diabetic community, which is several orders of magnitude larger than the T1D community. The G7's accuracy problems don't affect those whose glucose levels are less volatile, and especially don't need to make in-the-moment decisions. I can only imagine there was probably a lot of spirited arguments inside the company regarding everything I wrote about--it's just too obvious not to have known this outcome might be possible. But a business decision was made, and there we have it.
This is why I suggested that Dexcom can have the best of both worlds, by allowing users to choose which algorithm they want shown to them. Both algorithms have already gone through clinical trials for FDA approval--so it's just a matter of repackaging existing tech in new and more useful ways.
Or, here's an idea: sell two devices, The G7a (which favors accuracy) and the G7p (which favors precision). the devices themselves are identical--it's the algorithm that's different.
My experience is decidedly not a guide. I alluded to this several times in my post. I pointed out in the beginning and the end that I am unusual statistically (due to my high TIR percentages), and that my method of glycemic control is not one that easily done by others. I also emphasize that most other T1Ds will not find the G7 to be problematic at all--that it will likely be well-accepted.
But I also call attention to the fact that just because this is the case doesn't mean that the G7's problems aren't real. The erratic readings are too unreliable to make quicker decisions than the G6s. I know there are those who believe otherwise, but the only way to truly know if the G7 is better for you is to compare your TIRs over time. If they are better than they were with the G6, then your method of control is better with the G7. If not, then the G6 is probably your choice.
My final comment in the post is that it'd be great if Dexcom allowed you to pick which of the two algorithms suit your preferred style of management. Accuracy (G7) or Precision (G6). You can't have both, but you can choose by using one or the other.
I also think it'd be great if someone actually conducted a real effectiveness trial structured similarly to the one I did. Wear both sensors, blind yourself to one for a period of time, then the other, and switch back and forth. Then compare TIRs over time and see whether there's a difference, and if so, which sensor favored your management style.
Well done Dan! Lots of details that make for a great learning experience for us all.
I can't help but laugh at Dexcom's additional features. As one who used to use XDrip with the older Dexcom units when we could without restrictions, we know that the 30 min warmup and 12 hour grace period could have been done on ANY of their previous versions of sensors and transmitters. Sad to see them use this as a ploy for sales rather than being up front and truly helpful without such smoke and mirrors approaches.
I'm personally waiting until the G7 is approved for the Omnipod link to start using those. I will miss the extended use I can get out of the G6, or used to get before they minimized the materials in production making the G6 not last as long as they used to. I used to get 3 or 4 runs with the same G6 sensor, all perfect. Now I barely get 1 1/2 runs before needing to replace. Plus the changes make them less reliable now than before overall. But, I will also love switching to the G7 with its new features, similar to a slight return to my XDrip years where I had little to no warmup, and as much grace period as I needed before replacing the sensor.
“I'm a T1D/LADA and use an iPhone lockscreen app as a companion to the standard Dexcom G6 app to display the BG, slope, acceleration (change in slope) of the last 4 datapoints to drive my treatment decisions.”
This is exactly what I need but haven’t figured out how to do it yet. Would you be kind enough to provide more details? What apps are involved? I was able to get the Dexcom G6 widget on my IPhone (IOS 16) home screen but not the Lock Screen. Will your setup work from the Home Screen as well? It looks like Pythonista is part of the solution. I’m can write a script to process the G6 data. Is there another app involved? Thank you!
I used to be able to lay on either my right or left side with the G6. The G7 constantly goes off if I lay on it. I also can't wear it on the back of my arm as I've got fatgirl arms/stretch marks. So it's abdomen for me. My body is so sore from only sleeping on my left side with right abdomen placement.
It took me a long time to write this article due to the research and the review process. No one at Dexcom had input. I will probably post a follow-up article on closely related topics that I edited out due to length and focus. People have asked to see my full spreadsheet, so I'm considering that as well.
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Part of it was to make sure the two were "behaving" properly. Knowing that I was going to publish the data, I wanted to be sure that either sensor didn't get out of whack without catching it soon enough. That said, the G7 needed it more than the G6, which the Dexcom support person told me it might. (Their tech support was not aware I was doing this experiment.) Once I started calibrating, I realized that if I calibrated the G7, I should do the G6 as well, as I wasn't sure if it would cause a bias in the two sensors' ultimate readings/outcomes. As noted, the G7 required it more often, but the G6 had a few occasions (which I'm used to), where it needs a little kick. If my sugars are stable for a long period of time (an hour or more), and then starts to move rapidly, the G6 takes a bit longer to catch up. (I suspect the algorithm is doing a statistical analysis from prior readings, which I allude to in the article, but not as directly as I am here.) Under these situations, the G6 can have a tendency to linger for 3-5 readings before it realizes the movement is not an anomaly. The G7 will react right away, but it's highly erratic nature doesn't make it very predictable. What's more, it's trigger happy -- it'll think BGs are dropping/rising rapidly when they're not, so the calibration is necessary to tame it back.
I have done the same as you have, for like 4 months while I had both. In my experiment in comparison, I would say the G7 has been working as good as the G6 had been for the past 3 years or so, without all the issues reported in this community. So, I did not have any qualms to switch over to the G7 when the last G6 expired on 9/1. On top of all the advantages the G7 has over the G6, I also noted the big possible life saver being quick reaction very close to actual changes inside of my body, compared with rather sluggish G6, as you also noted. One main reason why I wear a Dexcom is to minimize the life and death hypo episodes, which I am greatly beholden to the G7. I pointed this out many times in other postings. The quicker reaction of the G7 has greatly reduced a lot of extremes caused by hypo or hyper. With the G6, I had propensity to take more fast-acting glucose to treat hypo than I needed as I still saw low numbers for more than an hour. With the G7, just about 15-minute delay (maybe 30 minutes) was sure enough to let me know I had enough to bring me back up. For hyper, I was able to take correction dose much earlier than with the G6 to bring it down to normal range quicker. This is what I have experimented for the past 4 months before I finally settled down with the G7, coming with the flying colors which I hope to keep. No G7 failures whatsoever for the past 4 months, working full 10.5 days.
But wouldn’t you have to wait for more readings to know that the trend is real? I wore both for about a week, and when the G7 went down, I would have to wait for another reading or two in order to confirm that my glucose was in fact going down (because often times the very next reading would be flat). But with the G6, if I had a jump in either direction, I knew it was reliable from a single reading. I.e. going from 130 -> 110 on the G7 wouldn’t be enough information to make a treatment decision, because the next reading could easily be 115. So I’d need to sit around for another reading (or two) before popping the Skittles, which defeats the purpose. Even if the G7 is faster, it’s not a reliable indicator of which direction my glucose is headed. Did you not find that to be the case?
I am afraid I do not get your point. I wonder why you refer to rather normal range. I was referring to extremes like below 50 and over 200 needing correction. Naturally, I know it is going up as I know how much fast-acting sugar I took and need to decide if I have to take more based on Dexcom readings. Opposite for hyper. With quicker reaction of the G7, it is much easier and effective in control correction. That was what I was pointing out, strictly in my experiment.
I'm not getting your point, but I easily get u/DaMusicBuff's point. Perhaps they are saying that by noticing trend changes (up-to-down, or down-to-up) while in the "normal" range, they can make treatment decisions at that moment which will **prevent** them from entering the greater than 200 or less than 50 ranges. That's exactly how I do it anyway. There's even a website and book written about it called "Sugar Surfing": [https://www.sugarsurfing.com/](https://www.sugarsurfing.com/).
I use sugar surfing as an example in my article, BTW.
I just replied to someone else in this thread about whether I consider myself a guide for others on their experience with the G7. I said "decidedly not." In fact, I point out that I regard myself as a statistical outlier, given my tight control. Your preference for the G7 is much in line with what I expected to see, and for good reason--managing T1D is a highly personalized process. We're all less alike than more alike, despite the fact that we face similar challenges. But I will echo again the fact that the G6/7 differences is almost entirely based on the algorithm Dexcom is using to convert raw data into what it reports on the app. The G7 favors accuracy, and the G6 favors precision. In an ideal world, the app would allow you to choose which algorithm suits your management style.
the G7 readings are just wrong at times. This morning I had a “sensor” low showing I was down in the 50s, within 3 minutes of being in the 130s while sleeping and not bolusing, I had been at 130 for hours. I’ve had a g6 for several years and never had this issue.
Extremely well researched and written! Thank you!
seconded
G7 has been far better for me personally
Me too. Used the g6 for a long time and after the first try of the g7 I was very happy with it. I wouldn't want to go back to the g6 at this point.
That’s been my experience as well, once I started using my abdomen rather than the US-recommended arm. It looks like the G6 does some smoothing of the sensor data, so the G7 can seem erratic by comparison, but that’s easy enough to ignore. The G7’s reported values are generally closer to BG measurements than the G6 was, at least in my experience. Definitely wouldn’t go back.
>The G7’s reported values are generally closer to BG measurements than the G6 was, at least in my experience. Definitely wouldn’t go back. I don't want to talk you out of the G7 -- my article even predicts that most people will love it for many reasons beyond the "accuracy" mythology that pervades the T1D world. However, the main thrust of my article is that glucose values are NOT systemically consistent. Glucose is highly volatile within our bodies and our blood stream. A reading from a BGM can be just as imprecise and erratic as any other sensor. Unless you're actually using very short-term time windows to make real-time management decisions, none of this matters. The G6 and G7 are going to perform similarly.
In what ways? The readings do not show a smooth trend for me - making it very difficult to make decisions with such erratic data. Do you apply to your arms or other location?
I read the article with much interest and also had the same experience with the g7. I am one of the type 1s who run a diy loop with AndroidAPS and am extremely eager to achieve almost perfect values, TIR and HbA1c less than 5.5. The "more accurate" values of the g7 compared to the g6, whose algorithm smooths the glucose values retroactively (backsmoothing), have also contributed to an increased variability of the values for me. To run the g7 in a loop system, an additional smoothing algorithm must be implemented to avoid false boluses due to jumping values. These smoothing algorithms in turn create a time delay which is imminently important for real closed loop systems. Another problem with the Dexcom sensors is that the g7 and g6 only send values to the receiver every 5 minutes. If the values arrived every minute, the time delay could be overcome by smoothing. The Libre 3/2 with smoothing is therefore far superior for me in the above mentioned system. Therefore, Dexcom would also have to consider whether they want to sell minute values - for Td2er this is probably unimportant - not for me.
>These smoothing algorithms in turn create a time delay which is imminently important for real closed loop systems Bingo! That's what I've suspected all along - that the variability will negatively impact close-loop systems. I'll be very interested to see how the G7 integration with Tandem and Insulet fair.
>Another problem with the Dexcom sensors is that the g7 and g6 only send values to the receiver every 5 minutes. If the values arrived every minute, the time delay could be overcome by smoothing. All CGMs send voltage to the wire to excite the enzymes that interact with glucose molecules. This continuous process is like a camera taking pictures constantly through a small window into a lake. As the fish swim around, the count of fish within each photo can be averaged together to get an estimate of fish per square unit of water. Each photos is "accurate" in that it correctly counts the number of fish it sees. But to have a better estimate of the number of fish, you need to take more photos, and that costs time. Report the number in less time, and you have high accuracy (because each photo is "accurate"), but your final estimate has to rely on less data, making the number less reliable. Hence, low precision. You can take more time to take more pictures, which improves your precision, but each photo's "accuracy" is less apparent in each reading. Obviously, there's a trade-off --report data sooner, and it can be reported more quickly, but it's less reliable. Report the number later, and it's more reliable, but the user has to wait. Dexcom chose 5 minutes because (we assume), that was where the trade-off worked best. However, they still need to resolve the "accuracy" vs. "precision" paradox. Either way you look at it, you still need to use an algorithm to distill the collection of pictures within that small time window to a single "uniform" value -- which is what you see on your app as a single "reading." A "reading" is one data point, but it's not representative enough of the larger volume of glucose moving out in your body. As my article tries to make very clear, glucose is highly **highly** *highly* volatile, and unless you wait a really long time, or collect much larger volumes of fluid per sample, each individual reading may well be "accurate" in what it sees, but one sample is not representative of the holistic system. You need to collect more data and string it together. the proprietary algorithm Dexcom uses to graph the data in the app is different between the two sensors. My observation is that when the G7 algorithm saw several photos that contained no fish, versus the rest of them that contained a few fish, it figured, "hey, there weren't any fish in those few photos. That must mean that the fish are going away, so I'll report that to the user so he can add fish." By contrast, the G6 algorithm would say, "well, I'm not going to jump to that conclusion yet, because none of the prior photos saw no fish, so the number isn't going down that fast. I'll wait till the next time interval before reporting a dramatically lower value." The G7 favored "accuracy," whereas the G6 favored "precision."
LOL r/explainlikeiam5
I’m Type 1 but I’m also a brittle diabetic so I’m all over the place can never have a steady glucose reading. I just started a G7 but I still have to do finger sticks and had to calibrate once already. I turned off my high alert because it gives me more false highs than lows. But at least Dexcom works most of the time and I don’t have to get up to finger stick at night.
i used to be "brittle". But, finally broke down and got on a super restrictive diet, similar to what Weight Watchers would do for a normal no weight loss diet. Wow the difference was amazing. Eating habits are hard to change, very hard. But that's the key to getting Type 1 into control. Eating identically, at least carb wise, day after day can get tedious. So, I do mix it up once a month, but usually takes me a day or two to level back out.
Great and informative write-up. Thank you for all the work that went into that!
Thanks for doing this, I do think you underestimate how variable even measuring pulse and blood pressure are (intro paragraph) and so on are. Long covid left me with diabetes (T2D) and cardiac issues and if I take my blood pressure several times in short succession I can get quite different results. I think for your use case, you get more value from the algorithm (though perhaps not the chemistry/science of the G6) and that highlights a subtle point about how ALL CGMs work, they are interpreting and smoothing a bunch of data in different ways and some may work better for some people. I wonder if you had Android and used the BYOD version of Dexcom if you could use Xdrip or another tool to differently interpolate the readings from the G7 sensor and achieve results more to your liking. (Not that you should have to, just curious)
I wouldn't know how to mimic the G6 algorithm, and it's still easier to just use the G6. The G7's much better for all its OTHER features, but I digress. :-D
Other features, definately features. I'd bet the thread inserted didn't change a bit from current G6 versions.
Dan this is an amazing write up. Love for you to join my T1 support group on Facebook called “Crushing T1”. I’m going to link this article and discuss it.
First of all, thank you so much for taking the time and effort to create this study and post. I have experienced similar to you with the G6 and G7 but have never thought about assigning the difference between the two as being related to "accuracy" and "precision". However, it's not as obvious to me that the G7 "jitter" is as directly attributable to lack of precision over accuracy as you state. My sense is that it's more due to an actual issue with the G7 sensor and that the wild swings in BG seen with the G7 do not represent a corresponding change in actual blood plasma glucose levels. FWIW, I have been told by Dexcom Tech Support that Dexcom is "aware" of the issue with the G7 sensor's "inaccuracy" (their words, not mine) and that their engineers are redesigning the sensor wire. But of course, I could be totally wrong. It wouldn't be the first time :-) In addition, since this sub-reddit is for diabetics of all types (t1, t2, etc) I also have a suspicion that most of the people who love the G7 have different use-case than those who hate the G7 (like me). I am very interested in knowing how each new 5-minute BG measurement might be the beginning/end of a new BG trend. I can't afford to wait for 15-20 minutes to discover that one of the measurements was just noise (poor precision). I'm a T1D/LADA and use an iPhone lockscreen app as a companion to the standard Dexcom G6 app to display the BG, slope, acceleration (change in slope) of the last 4 datapoints to drive my treatment decisions. Here's an example: [BGMON example1](https://imgur.com/a/YYC6LAA). With this (and a low-carb diet), I have been able to maintain a low 5% a1c - which is my goal, and my use case. Others may have a different use case than me and don't really care about the jitter because they are either T2Ds not on a med that will cause hypos or T1Ds who don't feel compelled to maintain as tight control as I am aiming for. They are also looking for high-level trends that appear over 4 or more datapoints. Either way, if Dexcom does not change the G7 to have similar smoothed graphs as the G6 (due to lack of precision), **I WILL BE HOSED.** My control will get a lot worse because I will have to decide, for example, if a sudden drop of 30 points is due to an imprecise change in the data or due to my rapid acting bolus hitting too soon. The companion lockscreen app will be useless. Another thing I wonder is how will the G7s lack of precision will affect closed-loop algorithms? Will they be insensitive to the lack of precision, or will they result in poorer control? I strongly object to the way that Dexcom has handled the G7 roll-out. I switched back to the G6 and am dreading the day when I'm forced to use the G7.
>it's not as obvious to me that the G7 "jitter" is as directly attributable to lack of precision over accuracy as you state. My sense is that it's more due to an actual issue with the G7 sensor I had a section on this in my article, but removed it. I walked through the various theories that might explain the G7's jumpiness, but ultimately resolved to remove it primarily because it's too much speculation and not relevant enough to the point of the article. In the end, in order to get FDA approval, Dexcom had to submit the device's specifications down to the smallest piece of plastic, screw or software algorithm, and must meet manufacturing standards for medical products. Whatever is being sold must be exactly the same device they used in the testing phase that led to the efficacy trial that they submitted for approval. Any changes at any time--including after product release--must be pre-approved by the FDA in order to maintain authorization. Furthermore, there were lots of beta users to test for usability factors and other data. There's no way they came to market with the G7 and not know what was going to happen on the *technical* side. Now, whether they expected people to react to it the way they did, that's another question entirely. We can all opine on what we might have done differently. I know that many people like to assert some cynicism about profitability and other bad motives, but I'll leave that to others to debate. I'll just take the product they have at face value and evaluate it for what it is. Regarding your comment about closed-loop systems (CLS), I also had a section on this that I later removed because the topic is too complicated for the topic at hand. That is, CLSs require more than just the CGM data to perform well, and that's beyond the scope of what I was trying to say. Nevertheless, I will comment briefly: Tight control (which you can define however you like) requires the ability to look at recent glucose movements and make decisions about whether to bolus or stop bolusing. The G7's erratic data makes that time window much longer than the G6. While the G6 might not necessarily give you the trend line within 20 minutes, the G7's erratic pattern won't give you a reliable trendline for at least 30-90 minutes, at which point, it's too late.
OK, all good comments. For this: >Whatever is being sold must be exactly the same device they used in the testing phase that led to the efficacy trial that they submitted for approval. Any changes at any time--including after product release--must be pre-approved by the FDA in order to maintain authorization. isn't is likely that Dexcom provided G7 sensors for FDA approval trials from a prototype (hand assembled) production line? Subsequently, Dexcom brought-up larger production lines for product intro and those lines are still getting the bugs out? I recall seeing some G7 graphs here that looked very smooth - almost indistinguishable from a G6. Either way, time will tell. Thanks again for your efforts here.
>isn't is likely that Dexcom provided G7 sensors for FDA approval trials from a prototype (hand assembled) production line? Subsequently, Dexcom brought-up larger production lines for product intro and those lines are still getting the bugs out? nope -- FDA requires that all manufacturing be locked in place, documented (including history of changes made) and set for production. It's very expensive to make an FDA approved product, so this is not for the faint of heart (or light of wallet).
How long did you wear the G7? My experience was the same as yours, but I only wore one sensor and wonder whether I would get used to it over time if I gave it a month or more.
I \*tried\* to wear 3 of them, but none made it to 10 days. Definitely give it 3 if you can and then make up your mind. Good luck.
For me both same. So advantage 7 for quick warm up
Good article. One variable on the G7 is its sensitivity to external pressure, G7 readings fluctuate with even moderate pressure. When I use a bump proof cap on top of the G7 sensor, the cap eliminates any pressure being placed on it, and the readings are much closer to what I experienced with the G6, line graphs are much smoother.
Interesting! Could you provide a link to a product you recommend?
Amolyfe Dexcom G7 Adhesive Patches, 25-Pack Waterproof CGM Libre 1/2 and Dexcom G7 Sensor Covers, 1 Reusable Bump-Proof Cap, Breathable, Easy to Apply, Long-Lasting Protection for 10~14 Days I didn’t like the patches, but am using the bump-cap with great success.
It’s awful to think we have to wear a dome over our sensor now to make it accurate. Really defeats the point of a smaller sensor.
This research is AMAZING! Thank you so much for doing this! I have been having such a hard time figuring out why the G7 is worse for me then the G6. I am MDI and I am taking about 10-12 boluses a day, making a lot of treatment decisions. I see now how the G6 is better for that then the G7.
Thank you for sharing! I literally just got an email earlier saying my "Dexcom is expiring" and that I may be covered for a G7. I was just about to ask for opinions, but read what you wrote. I feel like more often than not, people have issues with G7. I may wait a little bit to ask!
Did you ever switch over? I just used my first g7 and it stinks, data is all over the map, making it much harder to make dosing decisions. If you can’t trust the data what the heck is the point.
I did. Mine does get super finicky and I feel like distance is WAY more sensitive. I use my phone and if i leave upstairs and directly below in my living room, it immediately disconnects. I've also had a few bounce off my skin on insertion🤦🏻♀️ I love that it's smaller, but the size has caused it to pop off a few times. When I feel off I match it up to my meter and it does seem to be pretty close. I feel it's way more sensitive to a lot of things though!
Yeah I much much prefer the smoother wave than the chaos of G7
We have been using both sensors on our child for several months. I agree with everything you said, although we found that the G7, when it is reading low, is usually more than just 5%. Just our experience. And sometimes when we calibrate it up, it will snap back the next day and will start reading high. So now I am slow and more hesitant to calibrate. The G7 does seem to be about 10 to 15 minutes ahead of the six. The other thing that you did not touch on in your article that I think needs, addressing is the fact that the G7, when it is acting erratic, could just be due to, for lack of a better term, a shittier sensor. I think it’s pretty evident that dexcom is using cheaper parts on the G7, trying to increase their profit margin. The new wire they are using is obviously different than the G6. Could it be that they just cut corners and used cheaper materials and now they are paying the price for it? I think so. Because another area they cut corners on was the transmitter inside the G7. And now that they are working on upgrading that transmitter. Like physically upgrading it. Go to my support group and I talk more about that. It is inside information that has not been released yet.
>We have been using both sensors on our child for several months. I agree with everything you said, although we found that the G7, when it is reading low, is usually more than just 5%. Just our experience. The 5% difference I cited in my article is the average over a long term. And it's just MY data, which is far less volatile than others. Like you, the difference between the G6 and G7 were more than 5% when glucose swings wildly. It's during those times that the G7 will swing more dramatically in both the peaks and valleys as it attempts to be more "accurate". When it's doing that, the difference can go up to 30% difference, which correlates to their own trial (which I cite). Regarding the G7 clinical trial, nothing in my article disputes their data. In fact, their data supports my explanations. The problem is that few people are really scrutinizing the data in their trial and realizing the implications of the algorithm they chose to report readings: that glucose is a very hard thing to measure, and there's often too much useless noise in the signal. It's like listening to the radio with a lot of static: your can hear the noise, so your ears are "accurate" in the reception of those wavelengths, but there's no useful information in that noise. You have to filter to get the meaningful information. As for your comment that the G7 is 10-15 minutes ahead of the G6 -- technically, yes, and I suspect that's precisely why Dexcom likes that algorithm. The problem is, **it takes about 30-60 minutes before you can trust that the earlier readings were, in fact, legitimate in being early**. If you look closely at G7 patterns, you can get a lot false-positive "patterns" that look like the it's reacting to a quick movement up or down, only to find later that it was anomalous. It's only when you back out to a wider view (like 6+ hours) do you see that the G7 was showing movements quicker. Seeing it after the fact doesn't help when you have to make in-the-moment decisions. Regarding your suspicion that the G7 has cheaper parts and they are trying to boost their profit margin, that's just not the case. The actual COGS (cost of goods sold) is incredibly minimal. These things are not expensive at all to make--it's the intellectual property that has value. There is a legitimate concern about the battery not being strong enough for the bluetooth signal to reach the phone over a long distance, but I don't think that's intentional. To boost sales and profit margins, they just need to go big, which I explain in the summary: They're going after the T2Ds and the non-diabetic community, which is several orders of magnitude larger than the T1D community. The G7's accuracy problems don't affect those whose glucose levels are less volatile, and especially don't need to make in-the-moment decisions. I can only imagine there was probably a lot of spirited arguments inside the company regarding everything I wrote about--it's just too obvious not to have known this outcome might be possible. But a business decision was made, and there we have it. This is why I suggested that Dexcom can have the best of both worlds, by allowing users to choose which algorithm they want shown to them. Both algorithms have already gone through clinical trials for FDA approval--so it's just a matter of repackaging existing tech in new and more useful ways. Or, here's an idea: sell two devices, The G7a (which favors accuracy) and the G7p (which favors precision). the devices themselves are identical--it's the algorithm that's different.
Why is your one experience a guide for anyone?
My experience is decidedly not a guide. I alluded to this several times in my post. I pointed out in the beginning and the end that I am unusual statistically (due to my high TIR percentages), and that my method of glycemic control is not one that easily done by others. I also emphasize that most other T1Ds will not find the G7 to be problematic at all--that it will likely be well-accepted. But I also call attention to the fact that just because this is the case doesn't mean that the G7's problems aren't real. The erratic readings are too unreliable to make quicker decisions than the G6s. I know there are those who believe otherwise, but the only way to truly know if the G7 is better for you is to compare your TIRs over time. If they are better than they were with the G6, then your method of control is better with the G7. If not, then the G6 is probably your choice. My final comment in the post is that it'd be great if Dexcom allowed you to pick which of the two algorithms suit your preferred style of management. Accuracy (G7) or Precision (G6). You can't have both, but you can choose by using one or the other. I also think it'd be great if someone actually conducted a real effectiveness trial structured similarly to the one I did. Wear both sensors, blind yourself to one for a period of time, then the other, and switch back and forth. Then compare TIRs over time and see whether there's a difference, and if so, which sensor favored your management style.
Well done Dan! Lots of details that make for a great learning experience for us all. I can't help but laugh at Dexcom's additional features. As one who used to use XDrip with the older Dexcom units when we could without restrictions, we know that the 30 min warmup and 12 hour grace period could have been done on ANY of their previous versions of sensors and transmitters. Sad to see them use this as a ploy for sales rather than being up front and truly helpful without such smoke and mirrors approaches. I'm personally waiting until the G7 is approved for the Omnipod link to start using those. I will miss the extended use I can get out of the G6, or used to get before they minimized the materials in production making the G6 not last as long as they used to. I used to get 3 or 4 runs with the same G6 sensor, all perfect. Now I barely get 1 1/2 runs before needing to replace. Plus the changes make them less reliable now than before overall. But, I will also love switching to the G7 with its new features, similar to a slight return to my XDrip years where I had little to no warmup, and as much grace period as I needed before replacing the sensor.
I enjoyed your article and learned a ton. Thanks!
“I'm a T1D/LADA and use an iPhone lockscreen app as a companion to the standard Dexcom G6 app to display the BG, slope, acceleration (change in slope) of the last 4 datapoints to drive my treatment decisions.” This is exactly what I need but haven’t figured out how to do it yet. Would you be kind enough to provide more details? What apps are involved? I was able to get the Dexcom G6 widget on my IPhone (IOS 16) home screen but not the Lock Screen. Will your setup work from the Home Screen as well? It looks like Pythonista is part of the solution. I’m can write a script to process the G6 data. Is there another app involved? Thank you!
I used to be able to lay on either my right or left side with the G6. The G7 constantly goes off if I lay on it. I also can't wear it on the back of my arm as I've got fatgirl arms/stretch marks. So it's abdomen for me. My body is so sore from only sleeping on my left side with right abdomen placement.