I have a few questions about the Dexcom 7 after reading some previous posts. Someone mentioned that you should not calibrate your dexcom in the first 12 hours after insertion. Is this accurate, and if so, where did you find this information? I don’t see it when I look on the dexcom website.
Secondly, I was told by a dexcom tech person that you should not overlap sensors as it may “confuse” the app or something? Sounds like a lot of people do this in the grace period.
Thirdly, my readings ay night are so inaccurate! I am awoken by the alarm that I am low, then do a finger prick and i am fine. This happens so much that I often turn off my alarm on the dexcom at night. Does anyone else have this problem? I do NOT think it is due to a “compression low”, at least not all the time, though I know that’s what you all may tell me!
I really like the convenience of the dexcom, but honestly, I feel like I have to check with a finger stick 5 times a day as it is sometimes (not always) way off. My last sensor kept giving me low readings (over 30 points) after 2 days of use, so just replaced it. I often get 5-9 days out of a sensor, but very rarely the 10 days. I think my biggest frustration right now is that I am using many more test strips than my insurance will cover because I am using the dexcom, so I end up paying for them…
Jello @Jsich I wrote a thing on calibration so your post reminds me of it. I personally don’t calibrate g7 but it is what works for me. There is no fixed rule but if your CGM blood sugar is very different than your finger stick blood sugar then you might need to calibrate the CGM.
Just be aware that the CGM is measuring interstitial fluid and so the CGM is reading what your blood sugar was 5-20 minutes ago. Imagine if your blood sugar is rising fast, say after eating, your CGM may read significantly lower that a finger stick and this is normal. My recommendation is not to calibrate the CGM unless you see the trend arrow perfectly flat.
My last 10 sensors didn’t need a single calibration and even though there are differences between the finger stick and CGM the difference was either small or explainable due to the “lag” in interstitial fluid. I also realize that my finger stick meter is also inaccurate and has an acceptable error of up to 20% (a calculation, meaning the higher your blood sugar is, the more inaccurate your finger stick reading is)
I overlap my g7 by several hours every single session. I place my new one but I don’t stop the old one. After many hours I stop the old sensor and rip it off and start the new one. Flawlessly. I think the tech was confused.
Overnight false lows are common if you are sleeping on the sensor. It’s called “compression low” and it is due to squishing the interstitial fluid. The sensor is fine once you change positions. There is no easy fix for this though.
You have to do what works for you. Some people’s body chemistry or choice of location, scarring, hydration, and other factors leads to very poor CGM performance. I hope this is helpful , feel free to ask anything. Good luck☘️
Does the screen say LOW or does it give you a number? My Low alert is set for 100 and it sounds if I am below that. The alert can be set anywhere from 60-150.
Thanks for this, Joe. It is helpful, and I found it particularly interesting that you said that the lag time between the CGM and the finger stick can longer than the 5 minutes that I was taught. I have often wondered, based on my numbers, if the lag time was a lot longer and you confirmed this for me.
CGMs are considered accurate as long as their number is within ± 15% of a fingerstick. So if your fingerstick reads 70 and the CGM is around 60 it’s thinking you’re low.
I asked a trainer one time about how to cut down on low alerts and they suggested setting my target glucose a little higher. That may or may not be something you want to do.
Now if your CGM reads around 60 and your fingerstick reads 100 (random numbers here) that may be cause for calibration but do note @joe’s recomnendation.
Hi Jess @Jsich, of course you don’t see anything “derogatory” on the website - the web page is primarily an advertising sales page just like the TV advertising. In a years use, I’ve only gone through the calibration a few times; although I’ve done many finger-sticks when I’ve thought that my body was not giving me the feeling I should have with the current CGM readings.
The website does have a chart that can be read online or downloaded and printed providing the parameters as to when one may calibrate - for each CGM readings it suggests calibration if finger-stick is “below” or “above”. Specifically if the differences exceed 20% or 20 mg/dl. Note that the 20% / 20 mg/dl is a combination error-rate of 15 for BGM and 5 for CGM.
The Dexcom web Q&A has good information; I recall that is where I saw something “official” about calibration; also in the User Manual which can be read or downloaded.
I agree with you that the compression low is a real pain, especially when awakened from a good sleep. I’ve found that in addition to laying on the sensor - I’m guilty of that crime - that the sleeve of my sleep shirt can cause the alarm if it gets twisted. When I’m awakened by a “low” reading, when silencing I look at the three+ previous readings to see if the drop aws sudden; if this is so, I don’t bother finger-stick or food but, like @Joe, just shift my position and go back to sleep. If my assumption was wrong, the alarm will sound again and get me moving.
All-in-all, I’m really pleased with the G7 performance, yet I’ve shared my thoughts with the produce about improvements.
@Jsich if you don’t mind my asking, if the G7 your first time using a CGM or did you switch from the G6 or another device? And do you use a pump, or take injections? Knowing a little about you might help with replies.
I tried using a previous version of the dexcom years ago (I was diagnosed about 7 years ago at age 49. I also tried the Libre, and found both to be very inaccurate and also painful. I decided to try the Dexcom 7 several months ago, and have been pretty happy with it. I just put a new sensor in a couple days ago, and was trying to NOT calibrate, but the difference between the dexcom and finger stick today was over 15 points, so I went ahead and calibrated. Maybe that wasn’t necessary, as it is not 20 points! I am curious as to WHY it may be best to not calibrate. Do you (and Joe and Dennis) believe it interferes with the accuracy of readings?
Another topic - many nights from about 2 am to 4:30 am (when I get up) I get lows and then little “jumps” in my profile (several cycles). I am guessing either 1) I am going low and then my liver releases glucagon over and over, or 2) I am moving around more and getting repeated compression lows. Once again, I turned off the alarm at 12 am after waking up to do a finger stick when the alarm went off and I was not very low. I do have some peanut butter before bed each night. I am reluctant to be more aggressive with the before bed snacks as I have had nights where I am high (or what I consider high) during sleep and worry that interferes with the quality of my sleep. Then again, so do lows! So frustrating…
My philosophy is that the CGM is at least as accurate (in a clinically controlled environment even more accurate) as my finger stick. At work I calibrate sensors for scientific purposes (with 30 years experience now) and I cannot bring myself to calibrate a sensor with a something that is not at minimum, 10 times more accurate. If I calibrate my CGM with a finger stick it is statistically probable I am making the CGM worse, not better. If I disregard lag and calibrate while my bs is changing then I am definitely making the CGM worse.
The higher your blood sugar the more wildly inaccurate the finger stick gets. Same is true for CGM.
If my blood sugar by finger stick is less than 90 mg/dl and my CGM is showing that my CGM is level and not is not changing, then I might calibrate if my CGM was more than 20 mg/dl different than finger stick.
If my CGM says 190 and finger stick says 225 I would not bother calibrating because I know I’m high and need insulin and probably a walk. Calibrating to try to get high numbers to match does not (in my opinion) add value. So I look at these numbers and have adapted a “who cares? I’m high and I need to do something “ rather than worry or have anxiety that the numbers don’t match.
Continuing, 225 on a finger stick meter can have a 20% error. So when your finger stick says 225 your real blood sugar could be as low as 180mg/dl. (225. -(225 x 0.2)). Trying to get a “20 points off” at higher blood sugar is impossible with these instruments.
You still have to do what’s best for you. If you need to calibrate then by all means calibrate.
Jess @Jsich, as @Joe asked, why use a device that we all know to be considerably less accurate to calibrate your CGM? An example, on last Monday I had lab work done that included a fasting blood plasma glucose level - at the blood draw I put a marker on my G7 receiver. When I got the lab results the next morning, the lab result was exactly midway between two CGM readings - 112, 111, 110. Note that 110 is my set pre-meal target.
Something else to consider - do you know of any BG Meter Approved by US FDA for nolus calculations? Hint, there isn’t one. The first home use device FDA Approved was Dexcom G6; the second Approved device was the G7 - followed by a Libre.
This link will take you to one of several “calibration” topics on the Dexcom web page. Note the chart toward the bottom of the article:
There was a time when you had to calibrate certain sensors to get them started, and I think that remains the case with Medtronic proprietary sensors, but not with Tandem or Freestyle. That’s not to say it might not be necessary now and then, so calibrating itself is not bad - it just depends on if it’s actually necessary and what the goal is.
I just upgraded to the G7 about 6 weeks ago and did need to calibrate my very first sensor because my feelings didn’t match the CGM reading and the two numbers were way off - and not just in terms of the numbers themselves but the percentage difference (very important); and when I used the G6 I calibrated it occasionally as well.
When I do a calibration I find that the resulting reading is midway between the CGM number and the fingerstick, which makes sense, and I consider that my new baseline. I’ve heard (not necessarily here ) that some people want to keep calibrating until the numbers are nearly identical - but I would think that would result in the CGM trying to chase the calibrations rather than reading the numbers from the body.
I’m not a technical person and hope that makes sense - techies such as @joe and @Dennis can no doubt offer better and different explanations, and offer any necessary corrections to my efforts.
Again, calibrating isn’t necessarily wrong - the big question is, is it necessary?
Hi Jess, it sounds like you do not want to use a pump. I have had T1D for 47 years and started using a pump 30 years ago. It does have some downside, but overall the most important thing I got from it was a tremendous decrease is hypoglycemic (including severe ones) episodes. Whenever I get frustrated with using my Omnipod insulin pump, I remind myself of the severe lows that used to interfere with my life. Also, the lows that I do get with the pump are way less severe than when I managed with injections. Just something for you to consider.
@I’m coming in a few days behind others, but if I understand correctly you’re using MDI vice a pump, the lows you report are inaccurate G7 reports (evidenced by finger sticks). Most of the others above have hit on various points with good advice/considerations. While I understand the perspectives and reasonings of calibration, I disagree with discounting calibrations altogether. Rather, as long as calibrations are done with a trustworthy device (i.e. not tested when you’re high or low, but when you’re in range and stable), then I’d trust them to a large degree. I’ve had a G7 read both terribly low (60-70 pts lower than my trusted meter) as well as significantly higher than my trusted meter. The caution: A man with one watch knows what time it is, a man with two is never sure. So most of us have to have faith as to which is correct, which matches what you feel as normal (most can feel a low), which, has been tested by you against an even more trustworthy source, if available. And all this is recognizing the MARD of the devices (scientifically demonstrated potential difference from a known BG level) of both the G7 and finger stick device is fairly equivalent.
Also, you mention the potential of a compression low and seem to discount it, but don’t mention the location you’re using. While I’ve found the G7 much less likely to have a compression low, in my experience its not exempt from them and much more likely to result in “loss of signal” or “brief sensor issue” while I’m sleeping with the receiver (I use my phone) less than 3’ from the sensor at all times. My questions would be what locations are you using for the sensor? Is there a chance you’re experiencing some compression that may be impacting the readings and not realizing it?
All of this, as one of the others pointed out, is recognizing the interstitial tissue reading and actual BG measurement will rarely be the same. In addition, different people have widely different results due to body chemistry, reactions to the sensor materials, other and yet unknown reasons. That last line isn’t meant as a cop out, it’s just recognizing the facts. I hope you find what works best for you.
I place the dexcom on the back of my arm. Yes, I think I am getting a lot of compression lows at night. I tend to toss a turn A LOT at night, so there is really no good place to put the CGM where i would not get a compression low! I appreciate your statement that “people have widely different results due to body chemistry, reactions to the sensor materials, other and yet unknown reasons.” And I think our bodies change over time and impact our readings. As I mentioned before, I had tried CGMs several years ago and found them both painful and inaccurate. This time around, I have no pain and find the readings quite accurate. This could, of course, partly be due to updated versions of the CGM, but may also be due to bodily changes (maybe less inflammation?).
On another note, has anyone tried the Eversense CGM? My understanding is that there are few compression lows and that the MARD rating is about 8…
When I searched for “Dexcom Cover” on Etsy I found one of these. I’ve never tried them but thought you might like to check it out. You order an armband along with the cover.
@wadawabbit Dorie, do you have experience with any of the covers? I looked at them as potentials when I was using G6s, but then started using various positions on my left arm that seemed much less vulnerable to compression lows. Then switched to the G7 in similar positions. Except for one week/sensor, I’ve not experienced too many episodes. My concern about the covers is that they might seem great, but by there presence possible increase the area of pressure impact. Would like to hear from those with actual experience with them…
No. I usually recommend things I’ve had personal experience with I noted that I haven’t used these. But I but thought someone might like to try it to see for themselves if they worked.
) that some people want to keep calibrating until the numbers are nearly identical - but I would think that would result in the CGM trying to chase the calibrations rather than reading the numbers from the body.