Tuesday, February 23, 2016

How Accurate is My Blood Sugar Meter?

I often read other Type 1s comments about the “inaccuracy” of the readings on their Dexcom. But surprisingly, I don’t see all that much complaining about the inaccuracy of their blood sugar meters.

When using a Dexcom, you're suppose to calibrate it two times a day using data from a blood sugar meter, a.k.a, a glucometer. I sometimes get a meter reading that’s way off of what the Dexcom is saying.  When I get a surprising result, I’ll retest, and many times, I get a completely different reading from my meter the 2nd time around. Often it’s the Dexcom that’s right, and the meter that gave me a false number.
WE NEED ACCURACY in our glucose meters AND Dexcom.
Before you even ask, let me answer that yes, I wash my hands prior to pricking my finger for a reading.  This, as you probably know, can make a huge, huge difference.  (I used to NOT know that, and maybe that explains some previously unexplained low blood sugars after taking insulin.

In Steven Ponder’s Sugar Surfing book, he wrote about the current FDA guidelines for glucometer accuracy.  I’m basically copying this from his book and it says:

If the actual BG value is over 75 mg/dL acceptable values from the meter could be 20 mg/dL above or below the actual value and it would still be acceptable. If the BG was under 75 mg/dL, the variance must be 15 mg/Dl.  Most shocking of all--- in 5% of the test cases, the value can deviate from the actual reading by ANY amount.

Wow. That is alarming. And seems like a very dangerous allowance!

Like I said, when the test number seems a little off to me, I retest again.  And sometimes, I test a 3rd time for my tie breaker.  This seems a little ridiculous, but I guess it’s the best we’ve got.  Like Dr. Ponder says in his book, "The reality is that commercial blood sugar meters provide estimates of blood sugar levels."

If we want accuracy with our Dexcom, it’s got to start with the glucose meter readings we get for the calibration. So, I’d like to find out what is the most accurate and precise meter.  I have a few different meter brands tucked away and hopefully I can round up some test strips for them and test them against each other.  It could make a difference in what test strips I ask my doctor to prescribe when I go in for my appointment next month.

I’d love to hear what meter you’re using and how you feel about the accuracy. 


  1. Stripsafely has some links in the Citations section that are really scary. Studies show that some devices fail to deliver the +/- 20% for which they are approved- by a lot. It isn't just CGM calibration, most people who use insulin don't use CGM. Bad numbers means incorrect insulin dosing.

    Dr George Grunberger, President of the American Association of Clinical Endocrinologist spoke in an "Ask An Expert" Webinar with the Diabetes Patient Advocacy Coalition, one of his topics was inaccurate strips.

    See more: http://diabetespac.org/aaecoordinatingpolicy/

  2. Oh absolutely! It isn't just about CGM calibration. I was just making the point that I so often hear complaints about Dexcom accuracy, but not much mention about meter inaccuracy. Thank you for the link, Bennet!

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