Dexcom - Point Difference Between CGM and Meter

When testing your sugars using the meter and comparing to CGM… how many points do you want it to stay within?

For example, my meter had 206 but CGM had 230 so it was off by 24 points. Do I calibrate it or let it stay as is? I don’t always see a huge difference, maybe 10 - 15 points off and I let it slide but 20+ points should I go ahead and calibrate it?

The guidance is to enter a calibration if your meter is 20% away from your CGM. A meter that says 206 and a CGM that says 230 is off by (230-206)/206 = 11%. I would not calibrate. I am also careful to try to calibrate with a totally flat arrow and prefer to calibrate in a normal blood sugar range (i.e. 70-140 mg/dl).

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I agree with Brian. Good advice.

Also agree. Also, if you have the extra strips, take two of three measurements and average or adjust your cgm calibration accordingly. There are lots of other threads on strip accuracy but by regulation they are considered to be perfectly good as long as they’re within 20% of actual bg – even within the normal bg range.

Right, I assume that 20% rule is based on the 20% accuracy of meters. To give an example:

A meter reading of 230 could easily reflect an actual/true blood glucose (TBG) of, say, 200 (within that 20% blood glucose meter accuracy range), in which case, you could actually be calibrating your CGM reading (206) away from your TBG. Of course, that 230 reading could also reflect a significantly higher TBG (say, 260), in which case your CGM is pretty off. If it’s on the edge or if the reading seems questionable, it can be a good idea, like @truenorth said, to get multiple readings. Although if the issue is your meter is consistently off from your TBG by a certain amount, there’s no way to really prevent that from affecting your CGM as well (unless you either get a new meter).

I also agree with Brian, as a starting point. But then I think each person finds what works for them. In the beginning I think we expect more precision from meter and dexcom. But after a while we each learn how best to use the information in our unique situations.

Hello Everyone,

I too was having concerns about the discrepancy between my meter and the Dexcom G5 reading. I took thee following steps:

  1. I spoke to a diabetes educator (R.N./CDE) at my health care provider and was told that 15-20 % is the acceptable range.
  2. I started thinking about this, and realized that this person was sometimes paid to do patient education for this, and numerous other product, so I weighed her response, and decided it might possibly be a little biased.
  3. I contacted the educator help line at Dexcom, and got pretty much the same answer … 10-20% was what the FDA said was accurate for a medical device which did not directly measure a blood plasma value, which is what a finger-stick glucose value is considered.
  4. I then became away that “Dexcom” became approved by the FDA (US) and their Canadian equivalent for accuracy of values. There are numerous articles around on this. Seemed good enough for me.
  5. So much for this.