If your Dexcom is close to your meter reading, does it matter if you calibrate?

I just did a meter reading for the first time in a couple of days. My Dexcom G6 reading was one point off what my meter said. That made me wonder if there was even any reason to enter a calibration reading in my phone app. Does it make a difference going forward to enter a calibration that is pretty much exactly what the G6 says?

I think Dexcom’s instructions are only to calibrate if the readings are off by a lot – 30%, if I remember right.
With previous Dexcoms, excess calibrations could throw the readings off. I think the G6 has the ability to ignore some calibrations so it might not do any harm, but I would ere on the side of caution and not calibrate.

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I calibrate mine when it is more than 5 points off. I do try to always calibrate it in the same range of 95-105. I have found that it becomes more inaccurate at the higher and lower ranges but will stay pretty close to the accurate numbers from say 80-120 then?

I believe Dexcom says somewhere if it’s within 5 points? Maybe it was 10 points don’t calibrate it? But they also think 20-30% off is okay sooo…

I try to never calibrate because a single calibration voids the manufacturing calibration. I only calibrate if on day 2 the G6 is consistently off by more than 15%. This happens so rarely that I not even remember when it happened last. From day 2 forward the G6 is always spot on, whether I calibrate or not. My reasoning is that any calibration on day 1 is most likely harmful and has to be corrected later with another calibration. I accept that I have to take day 1 readings with a grain of salt and there will be sunshine from day 2 to 10.


I agree with @Helmut. I try to never calibrate on day one of a new sensor. Of late however, I insert a new sensor (with no transmitter) 24 hours before I switch the transmitter over to the new sensor. This "pre-soaking’ the new sensor has virtually eliminated my experience of day 1 inaccuracies.

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I also don’t calibrate very much. I did one time on the first day and I lost the sensor. Most times, I find if it is off I just watch it and it eventually comes in line. The big joy to a G6 is not having to calibrate!

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Same for me, but I still BG test to make sure its on track. I wish meter bg could be entered, without it being considered a calibration.

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Question; how do you know it is “off”? I was told that, once I switch to a G^, it is more accurate than a finger stick? That true?
My experience with the G5 doesn’t justify that kind of confidence I’m afraid. Oftentimes, it will stop giving any readings, for 30 to 120 minutes, then when it comes back alive it’ll back fill all the missing readings

The being accurate was a huge concern for me when I switched to the G6 with Tandem IQ. I was always testing when using the G4 because the numbers just were not as close as I thought they should be.
But with so many people using the DIY systems and having the pump raising and lower insulin levels based on CGM results, I figured it was good to go.
I am pretty sensitive to insulin, currently running 1:90 and use about 25 TDD. So my worry was, it doesn’t take much to swing me one way or the other. And I must say, since removing myself from the system and wigging out over every number, I just let the system do it’s thing. My old time in range goal was 70% now I have pushed it to 80%, my deviation was 50 now it’s 40 and I want my urgent lows under 1% and lows in single digits. This system has made all that happen with no work.
One of the endos I work with at UCSD on clinical trials (has diabetes) told me to just relax. The sensors will catch it and he is right. I have had no problems with the system turning down the insulin rate based on my sensor and my numbers have gotten better on a time in range standpoint. My a1c is the same but I am more in range, less deviation.
It’s not my call. This rests with you and your medical professionals, but I say let go a little. See what happens if you don’t test for a week. Diabetes, it’s all about daily experimentation!

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I agree. I don’t worry about it at all unless I have symptoms that don’t match the number. Even in that case, I generally find the meter is right and my instincts are wrong.

Now, as far as day-1 is concerned, I’m presoaking so the day-1 hystereses is a thing of the past for me. I do find that in the first couple of hours the G6 readings are high, but it drops back in place thereafter. I think that’s because the calibration curve has a steep slope initially and the higher signal after presoak vs without maps to a higher BG number on the curve. Once you reach the time where the calibration curve has a lower slope the stars align again.

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Paytone - quick question - how long do you typically presoak for ?

Generally I start the presoak before bed the day before the current sensor is set to expire. Then a place the transmitter shortly before the current sensor expires. So generally the presoak is between 10 and 20 hours. I tried 6 hours once and that also worked. I’d say experiment and find what works best for you.

Thanks - I’m just a little shorter than you I think, typically start after showering the morning of the change and change at night so I’d say 12-14 hrs give or take.

Interesting, my G5 does the same thing. I shave area in the morning and then insert sensor. Sensor soaks all day until next morning 5:45 AM so my pre-soak is about 21 1/4 hours. When I swap the transmitter to the soaked sensor, my readings are about 15 - 20 points high and then come back to normal within 1-2 hours.