There was a thread recently, which I wasn't able to find, that discussed the calibration frequency for the Dexcom. There were a number of suggestions in the thread.
I couldn't remember what I was told during my 7+ training, so I asked Dexcom support. The response I got was the following...
7+ and G4
Calibrate with 2 meter readings at startup, as prompted.
Never enter two meter readings within 5 minutes, except at startup.
Calibrate when prompted, normally every 12 hours.
If you happen to take additional meter readings, like prior to a bolus, enter the additional readings only if the 7+ reading is more than 20% off from the meter (plus or minus).
Additional meter readings can be entered into the G4 at any time, even if the G4 is within 20% of the meter. However, it is still necessary to follow the "not within 5 minute rule" mentioned above.
I have a 7+ and never actually do two calibrations for startup. I tried the first few times, and it was just a waste of a strip since they were always within a point or two. I only enter a calibration when it's not trending right. Sometimes that can be days. Why tell it new information if it's doing fine without it?
The 2 within 5 minutes is annoying. I've still never heard a reason why when you enter a number, it spits out something 5 below typically. Entering the number again will bring it a little closer, though maybe the next reading will not have changed because of it. But please, just show the number I actually calibrated to!
I thought the same when I was told to do it during training. At that time, I was told to check my left & right hand. I was quite surprised to see the difference in the readings. I forget the actual numbers, but I was literally shocked - having never tried to check both hands at the same time.
Since I've seen different meter readings from each hand, I don't question a little variation in what the Dexcom shows. I assume the reason that the Dexcom doesn't simply match the meter reading is because it isn't measuring blood. It has to read interstitial fluid and calculate blood glucose. It has to do some prediction, since the interstitial reading lags blood glucose.
It doesn't matter how it's measuring it, if you enter 120 it should then be showing 120 until 5 minutes passes and it can show a few higher or lower. But inevitibly I will enter 120 and then it shows 115. :/
Tech support told me the same thing for 7+, with one exception. They told me if the meter was 80 mgdl or lower, only to calibrate if the the meter was more than 20 mgdl different, not 20%.
My CDE told me to take two separate reading at start-up because the meter can be ± 20%. My strips are covered by insurance with a small copay, so I don't mind "wasting" a strip. I also take two readings if the a reading differs from the CGM by alot and I don't feel the way I should based on the test result.
I expect there to be a difference between the meter test and the CGM because the CGM is approximately 20 minutes behind the meter test. That is why, when I calibrate, the CGM reading usually doesn't match the meter reding
Thanks for the info! I am switching from the 7 to the G4 in nine days (but who's counting lol) and did not know that you can enter all of your finger sticks in to the G4. Yet another reason I am excited to get started with it. :)