G6 reading: 124. Finger stick: 132. I didn't believe the finger stick

So I retested on another finger. Result? 124. It’s a crazy world I live in now that I believe the G6 over some finger sticks. BTW, I had just washed my hands thoroughly before testing on my usually very trusty Contour Next Link 2.4.

My G5 wasn’t far off: 128. I’m wearing it as I’ve transitioned to the G6. Just for grins.


I went from finger prick (blood) to CGM ( interstitial fluid ) and was concerned about the readings not being identical. A Certified Diabetic Educator explained the CGM is more about the trend and not so as much about the current blood reading. The CGM has a delay when compared to blood readings. And when holding steady both will be close. A video helped me to get a better understanding. It’s on youtube and has the title “Do you know the difference between testing interstitial fluid vs blood glucose?”

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A man with one clock knows what time it is. A man with two clocks is never sure.

132 vs 124 is such a minor difference I don’t see any problem to be solved ???


Thanks,but I know all that. I’ve been on a CGM for over 2.5 years. :slight_smile:

Did I say there was a problem? What I wrote was that instead of implicitly trusting the Contour meter finger stick readings which have always been my source of most accurate data, the G6 accuracy prompted me to take a second finger-stick reading because in a rare turnabout, I didn’t trust the meter reading. It is nothing short of amazing that I trusted the G6 over the meter.

Please don’t read into my OP that I think there is a problem to solve. My remarks were meant to demonstrate the accuracy now obtainable from CGM tech–something that I know won’t occur every day. :slight_smile:

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I’ve frequently seen the cgm off by tremendous margins… over 100

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I’m often suspicious of my CGM readings but as a practical matter the only real “problem” is that they lag fingersticks by 20 minutes or more which has taken me and my brain a while to get used to.

On weekends I’ve been doing a LOT of work on my 21 year old car the past couple months, and having a CGM instead of having to do fingerpricks means the world when your hands are covered with grease+two decades of grunge from the bottom of the car. It used to be when my hands were way too filthy I would take off my socks and shoes and do toepricks but that is such a PITA.

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When I have checked my G6 and found it to be accurate, I follow history that it pretty much stays that way and only check it off and on. I go days now without finger sticking! Love i! But I’ve had great success with mine staying accurate. Like last night my new pod wasn’t performing well and I went up to 153, did a fingerstick and I was 149. So I did a pod change and woke up with a lovely 88! No need to check, that’s pretty much what I wake up to when my DP is behaving.

Of course now during that 2 hour warm up I do more finger sticks to see what’s going than I do in days.

I hear ya. I remember when the FDA certified it was ok to bolus from G5 readings, there was a lot of discussion of fingerstick-vs-CGM accuracy, and one thing that always came up was that, y’know, it’s not necessarily the case that your BG meter itself is all that accurate—the standard error margin is something like 20% and they vary widely by brand (with ContourNext ranked at or near the top). Part of the thing is that there’s kind of a misleading impression built into both devices just in the fact that it’s giving you this very specific number for something that by it’s nature isn’t really that specific. What’s the range of BG across the entire vascular system at any given time? Anybody know? Heck I’ve seen fingerstick variants of >10 pts when I thought the number was wrong and checked with a different finger. So who’s to say it’s the fingerstick you should trust over the CGM?

So the argument went, but with the G5 I just couldn’t be emotionally separated from the perception that the meter was more accurate so that’s what I was going to go by. I didn’t give up that conviction with the G6 either… at first. It took a month or two. Now I rarely fingerstick at all, usually just once first thing in the a.m. just to check that everything seems to be on track, and that’s it.


I am well aware of the idea that CGM lags by roughly 20 minutes, but since my bg’s don’t move super-swiftly most of the time, whenever I do test, the readings are very similar to one another. The G5 needs to be calibrated once or twice daily to maintain good accuracy FOR ME. Day-one of the only G6 I have worn, the accuracy was horrific. I’m on day 7 today and still doing great. I hope I can do a restart so that I can build up a stash of the G6’s.

HOLY BATMAN!! It happened again this morning–finger stick over 170 while G5 and G6 indicated around 140. Retested on other hand and nearly a perfect match with the G6 and G5.

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Wow @Dave44 what a difference between hands!

I know. I’m baffled as to why it happened the first time,because I had just washed my hands. Today, at least, I hadn’t washed immediately, and so MAYBE there could be something I touched that had a bit of sugar on it, but I’m doubtful about that as well as knowing I used a good sized drop on the higher-reading left-hand.

In the G4 days and for probably the first few years with the G5, I tested 10+ times a day. Since I’m no longer testing as much (I’m still on the G5), I have a lot of strips left in reserve. edited to add: By saying I’m not testing much, gasp, there are days I don’t test at all now!

The next time I test, I’ll test on both hands to see if there is much of a difference between the fingersticks - and I’ll pay attention to what Dex says too.

Usually when I calibrate, there isn’t much of a difference, but I’m testing the same hand. I tend to favor my left hand for fingersticks, as I hold the lancer in my right hand.

I do the same thing. And until a couple days ago, I’ve not been in the habit of testing twice; once from each hand. I only did that because the reading was so far off of the two Dexcoms I am wearing.

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I thought that was the reason! :slight_smile:

Thank you for sharing your experiences with moving from the G5 to G6, especially this transition mode! It’s something I’ll eventually have to do too, go to the G6, and the sharing you and others post, is helping to prepare me and a lot of others!


I moved to the G6 with much trepidation because I hang out at a number of Dexcom FB groups where there is a lot of complaints of repeated failures (dunno if it is user error or what) but on the other hand, lots of folks write that they have hardly any problems over the course of many months. Now that I am wearing one myself, I know that a G6 can perform super-well, which is not to say that I won’t get a lemon now and then, but at least I can see for myself that it is a remarkable sensor.

I won’t mention the size of my strip cache. :slight_smile:


About half way through my G5 usage, when I finally figured out that using the G5, Xdrip, staying VERY well hydrated, and where I placed the G5, all amounted to trusting it more than my meter.
I also quickly learned to not calibrate AT ALL after the initial calibrations. Xdrip was far more trustworthy.
I used to go days, or, WEEKS without testing!
So, the change to the G6 wasn’t the huge leap forward for me.
What I learned with the G5 though was simple.
Stop trying to blame the system. It WILL work. Instead, figure out how to make it work FOR YOU!
For me, it was drinking a LOT of water, using xdrip, finding the correct insertion angle, and NOT calibrating.
Once I had those things figured out, I was golden!
The G6 basically gave me a wonderful applicator that no longer hurts, and is MUCH easier to hit the right angle for ME. It also gave me a thinner profile that gets caught on clothing, sheets, etc. a lot less. Etc.


I hope this helps.

Some people need to recall that all measurements have or should have an error included therein (often not stated but implied) that is particular to the tools of measurement and the user. This is something in addition to watching one’s significant figures, and using them properly.

For instance, if I use a cheap wood ruler to measure the length of an inert metal bar, and it looks like 13 and 2/16 inches, I probably cannot make the claim the length is 13.125 inches in length with 5 significant figure. It might be that the accuracy of the ruler is plus of minus 1/8 of an inch. So I then might say that I measured 13.125 inches +/- 0.125 inches (as the error). Further, perhaps two sig figs is best, so the metal bar is then merely 13 inches +/- 0.12 inches error. But I cannot presume that the tool (the wood ruler) or my use of it is accurate and precise. I might by my method introduce some small error too in precision, which is different from accuracy.

When you use a home glucose monitor, it has an error that is inferred with every measurement, unique to the meter. Some meters are off by as much as a few digits up or down. If you want to demonstrate this take ten measurement in a row at approx the same time using only one meter. Here’s a sample data set one might get: 132, 135, 127, 130, 125, 133, 130, 131, 138, 128 mg/dL. You cannot say your true value was any one particular figure but it is safe to use the median or the mode as 130 mg/dL. However, a better way to say it might be 130 mg/dL (2 sig fig) or 130 mg/dL (3 sig fig) +/- error. The error in this case involves the sum of the sq’s which might be in the end +/- 3.7. So maybe your true number was 126, or maybe your true number was 134. It’s all pretty much the same number given the imperfect tool you’re using to get a value.

Now we’re using two different tool, a home meter and a CGM to get to different value to compare, both with limitations, and both not perfect, and both with errors implied therein.

So 124 reading on one device and 132 on another is not any surprise whatsoever, really. Plus the G6 might lag slightly behind the finger stick too. I am not advising you on which number to use although I have a method myself. If you think you have this down to a highly accurate and precise means of determining blood glucose level and injecting insulin, without error, one is kidding himself. For one thing, if I told you to show me some particular amount of insulin, let us say, 47 units, I guarantee you if you did it enough times some would be 46, some would be 47, some would be 48, etc. . . and that is more than a 2% variation just for this. Also site have different characteristics, some are better and some are worse than others. So, 47 units in one site might be different than 47 units in another site in terms of response. And then, do you wish to assume every vial or pen of insulin has identical activity – because they do not. Everything is in a range and has a certain error.

Basically, your two readings of different values are reasonable and within the error range. 134 and 124 might be considered the same value for practical purposes here. it’s almost like saying 129 +/- 5. It’s not the same as that but you get the point. That’s about a 4% error in this example. I do not know the error range on your meter. It is available information. There are different methods and practices to evaluate statistical significance of particular errors. I wouldn’t be surprised at all if a meter has a 3 or 4% error rate that they state in the literature. In fact, I would expect it.

This presentation only discusses one aspect of the CGM issues, not the whole story. BTW, I have a new G6 and haven’t used it yet. I hope to set it up today. I am not expecting perfection.

Do not let it drive you crazy.


This sounds a little obscure, but I imagine it is a more prevailing issue than it seems. I can totally relate to what an improvement this is - must make for a much more relaxing experience with your car! (I’m picturing myself making meatballs or chicken cutlets with crumbs and meat on my hands and how frustrating that can be and it’s only for a few minutes! - not an apples to apples comparison, but it’s what I have to pull from :upside_down_face:)