Major differences with minutes of blood sugar check

I was worried that my sons CGM was off but when I did a finger poke it gave a # off by over 150. I retested got a number within 15. I retested again and got a number within 5 of my CGM. My spouses glucose monitor was off by 50. I have used controls and it says they are in range. I have made sure he washes his hands before taking a test. Has anyone had this happen or is my Glucose monitor accucheck just junk. We had this happen before and our physician threw it out and gave us a new one. I am glad his CGM is always been less than 5 off, but within 3 minutes period that much change is impossible.

all home BG meters have a minimum accuracy of +/-15% over 75 mg/dl

even with a good control solution check, at a higher number like 200 would put his actual blood sugar between 170 to 230. That’s a 60 mg/dl spread in the actual blood sugar versus what you are reading on your meter.

looking at it the other way, if his actual blood sugar was 175, meter 1 could possibly give you a reading of 148. meter 2 could give you a reading of 201. and both would pass control solution. these tests could be run simultaneously as time is not a factor in this kind of test.

It is sad. Whomever passed all these rules and regulations must have never suffered from diabetic and had to do all this FUN math to figure out insulin for food and correction factors. It is a bit overwhelming and keeps my mind ticking.

Keep in mind Stacey @staceybartleyandrade that what we have now - minimum accuracy standard for digital glucose meters of +/-15% in 15 seconds - is actually a big improvement in both time and accuracy. @Joe and I both remember when a “simple blood sugar test” took a couple of days before we got the results and then depended on the skills of a lab technician. Joe may be too young to remember, but in “the old days”, blood taken from a vein was dribbled over yeast and technicians watched [for a day or two] to see what grew and then made a guess. Yep, no such thing as a re-check within a matter of minutes.

Yes, these digital BG meters of recent years are a wonderful improvement and God-send for us even with the “permitted” inaccuracy of 15%. Keep in mind that the 15% or 15 mg/dl is the maximum variation. I suggest that we all review independent lab-test reports of all major-use BG meters and buy only the most accurate.

Interesting information. I guess I have never taken all of that into consideration. I really appreciate your input.

I’ve read that the Contour Next has an accuracy of 10%

I’ve had that happen occasionally and when I called Dexcom they asked if I had used any acetominophin for pain relief. I can’t recall if that was the problem every time but there have been occasions when I’ve used Tylenol instead of Advil and apparently that caused the issue.

Most important to understand!
The meter can have up to 20% inaccuracy. The usual is 15% , but up to 20% is ok. Then the CGM can have an in accuracy of 20% of the finger stick.
So, a large variation can occur pretty quickly. The best thing to do is use judgement when something like that happens. If it sounds like B.S. then it’s B.S… If when testing it feels about right then it will be close enough to use for treatment.if needed.

I look at it this way. Whoever set this system up set it up for government work. Attitude of ehhh it’s close! Not set up for rock n roll where when it’s right it’s right. Not very scientific, but kinda explains it. You’ll drive yourself crazy trying to get to the bottom of why it’s off, it just is! Retest and go on.

When i test the first one can be way off. As much as you have said or more. I use my inner blood glucose monitor( my brain), if it feels right I go with it. I stopped wondering why this happens, I just adapted, overcame and improvised to get where I need to be.
I’m very analytical and test and asses everything. It drives me nuts that it’s this way, but I had to accept the fact that this stuff happens., and I have no control over it. Kinda like being diabetic! I can eat the same thing at the same time each day. And the results can be different from day to day. In a perfect world it should be repeatable and dependable for results. Our bodies are too complex and different for this to happen. You have to take this into account. I try to explain this to my dad, a retired chemist, who absolutely does not grasp this concept.
He will argue me until he’s blue in the face that this can’t happen! He doesn’t understand or accept the critical problem which his statement. Our bodies are not in stasis! Because of this results will vary. The variation can change from minute to minute or day by day. In order for full repeatability, or bodies cannot change! They must remain exactly the same. It just does not happen. So due to that. Results may vary!

Hope it helps to kinda explain why and what’s happening with the testing issues. It’s an easy explanation, but the concept is very hard to accept. But coming from a biological standpoint, it gives you something to think about and gives you a way to comprehend why the differences can occur.


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Contour Next is what I have always used, even before my CGM . It’s amazing how close the Bg & Sg readings are.

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Hi Joe,

I too questioned the differences between my G6 and my finger stick readings. I started to accept the CGM readings because, I don’t really know which one are actually correct and/or precisely accurate. I determined that the finger stick and the CGM could either be correct and decided to trust the average between the two, since there was not a huge difference. I talked to my doctor about it and we both agreed that just because the finger stick said, for example, 120 and the CGM said 150, we shouldn’t assume the finger stick was always right on and that the CGM was giving me the wrong reading. How do we know that the finger stick is right and the CGM was “off” by 30, or visa-versa? Right?

Hey Pete, for the most part, yes. I do a lot of calibrations for instruments and I always put more trust in the thing I used to calibrate the other thing.

Finger stick machines are pretty good now, Not too long ago, they were +/-20% or more. Now the industry is +/- 5-15%. and if you look at random error for the CGM such as Dexcom… I suppose today I would take either one as “right”.

I just wanted to add that I recently wore two CGMs at once for about a month. (Long story.) My Guardian CGM AND my Dexcom G5 were almost always VERY close to my Countour meter. . I must say that I had had some very big discrepancies with my Dexcom in the past (as much as 100 points off on multiple occasions. At the time using Accu Check Expert Pro meter.) But, so far, the Medtronic CGM and meter have not let me down. I’m sort of surprised, since, I read that problem with others. (No longer have Dexcom, as transmitter finally died.)