New to G6 with BG readings very high

And it should remain roughly 10 points behind your glucometer reading because it is reading interstitial fluid and not blood.

Wow, I was not aware of that at all as an additional idiosyncrasy that has to be dealt with the Dexcom G6 CGM. I am on medicare and still on the G5 until Dexcom moves me to the G6 but at least that is not something we need to take into consideration with the G5. We calibrate the interstitial G5 glucose reading twice a day to our fingerstick blood and the numbers most of the time are identical or near identical when taken with a steady 3 dot (15 minute) steady horizontal arrow. With the G5, the Dexcom algorithm automatically adjusts for the difference.

Another reason then that I am not in any rush to get on to the G6 if the G6 algorithm does not automatically calibrate for the difference between blood and interstitial fluid. It seems weird Dexcom would take a step backwards on that one. Just out of curiosity, is this difference noted in the G6 manual or did you come to this conclusion through some other means?

@CJ114 It doesn’t even matter if the G6 takes it into consideration for the actual calibration as you can’t tell if it’s reading right unless you are comparing the same numbers? So to be able to know if it’s accurate you have to compare a finger stick and wait 10 minutes to compare it with the sensor number, since an interstitial reading is behind by 10 minutes.

In the manual for the actual calibration it wants you to enter the finger stick number within 5 minutes on your reader for the sensor. So I’m assuming it’s doing some kind of adjustments.

This is why you don’t appear to have noticed the lag between blood and interstitial fluid readings. Interstitial fluid lags behind blood, always. If your levels are not changing then you wouldn’t notice a difference. If you test when your levels ARE changing - dropping, or rising after a meal - then you will see the lag.

As far as I know there is no technology that can compensate for the differences in the two completely different types of fluid without just guessing where you’re going based on where you’ve been. I’d love to be wrong, if you have a source for that.

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That is why with the G5 I only calibrate when I have had a steady reading for 15 minutes (3 dots on the Dexcom receiver). That way the interstitial fluid CGM reading and the blood from fingerstick should be and usually are near identical.

Then you won’t need to change that with the G6. You are already compensating for the lag time yourself.

Is this not why Dexcom tells us not to calibrate when levels are changing? We need to always make sure that we calibrate only when the arrow is steady horizontal. Since I am aware of the timing difference between interstitial and blood reading, I always make sure to have 3 dots and a horizontal arrow during those 3 dots (15 Minutes). If individuals are calibrating while their glucose levels are changing, then the calibration error is self inflicted, not a problem with the technology.

Lol…I enter the number I want to enter anyway to get my CGM to read within 5 points of my fingerstick. I guess I cheat and I’m not sure what I am doing to my algorithms?

But since mine is usually within 5 points when I do my comparisons after that it seems to work for me.

PS New people don’t pay attention to me!!! LOL…Do what your are supposed to per Dexcom, because we all respond differently and if you want Dexcoms help you have to follow their guidance!

I’m sorry if I misread your post, it sounded as though you didn’t understand Willow’s comment about the 10-minute lag and that there was some sort of “idiosyncrasy” with the G6.


I have no problem with people cheating the system if it gets them better results. I do have a problem, however, with people that do not follow Dexcom instructions and calibrate while their BG is rising or falling, screw up their algorithm and then claim that Dexcom is a piece of junk and rarely gives them correct BG numbers.

My Shanghai office used to be near the Mercedes dealership and it was interesting to see wealthy folks buy a new car and within a couple of miles, roll it or just have a crash. They had never learned to drive but since they were successful in their business ventures, they assumed they would be successful driving without taking any lessons. After their crash, they would never admit they did not know how to drive as their comments were always about how unlucky they were that day and there must be something wrong with the car.

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Yea, that’s why I added the PS lol…I don’t want to screw up a bunch of new people that messed up their algorithms from entering different numbers. I extend my sensors and always get about 25 days out of them, so I never have the need to call in a bad sensor. So if I mess up mine, I don’t really care except I have to hassle putting on a new one.

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I did dig thru the trash and actually found the little pieces of paper but the number was gone like disappearing ink😯
What a great idea to make taking a picture part of the routine!

Since I restart mine I just keep everything original with the sensor applicator still in it’s plastic container in the cupboard until I switch to the next new sensor. I also write the day I originally applied it. It’s just a habit I started and that’s easy for me.

Dexcom was all set to send me another months worth of G5 supplies, but I wanted the G6 because this month they are supposed to be updating to the closed loop Control IQ.
I had put off using a pump for the first 60 yrs. of T1D, so in 2017 I got my first pump, and now I want every update available.
So I got a new prescription from my MD, and went to Walgreens, and had it in a week. Since G6 has been approved since June 2018, I had waited long enough.

Dexcom has their direct re-ordering process pretty much under control right now so I don’t want to mess with my re-orders. For several months, the monthly would arrive sometimes early, usually a little late, sometimes a duplicate order in other words every month was Dexcom mystery package month. For a while they sent me a new transmitter every other month so I have a stack of unused G5 transmitters. I just got a message on my Dexcom reader to order another transmitter as this one only has 20 days left. Now will see if that automatically triggers Dexcom to send me a complete G6 package or if they will continue sending G5 supplies. Either way I plan to run out as many of my G5 supplies as possible after G6 arrives to build up a little buffer supply of G6 items. I hate wasting my time and Dexcom time on the few occasions a sensor fails so rather keep a small stash so I don’t need to call them. Dexcom packages always seem to come at the most inopportune time as I do a lot of International travel and my monthly package usually arrives 1-2 days after leaving for a trip.

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The calibration curve is built against whole blood so the correction is accounted for.


If anyone wants to, if they are using Xdrip, they should view RAW data.
What you see as three constant numbers, ARE NOT. Or, I should say, RARELY ARE.
What the transmitter actually reads is not the same as what the algorithm shows us.
Point is, what you think is stable is NOT. And thinking that the readings should be perfect, or damn close. Isn’t going to always happen.
If they are close, DON’T SWEAT IT!
Obviously the first 24 hours can be a bit squirrelly for some/most people. The pre-soak thing can remedy this for most people.
Restarting the sensor will prolong the good sensors (you obviously don’t want to restart a poorly performing sensor.)

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I haven’t experienced this.

I’m glad you’re able to get that level of consistency.

If I had been forced to wait for 3 consecutive readings when I was using the G4, I never would have been able to calibrate it. Even with the more accurate G6, I regularly will see readings with 0 COB and 0 IOB that vary by 1 - 5 mg/dl. Yesterday, I happened to be paying attention and had these readings over a 15 minute window: 89-93-89. If a calibration had been required at that time, I would have gone for it.

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I would too. That 15 minute period on the G5 would have shown a steady horizontal arrow during that 15 minute period on the Dexcom receiver. There is some leeway before the G5 shows an ascending or descending trending arrow rather than a horizontal arrow and the 89-93-89 would, I believe, have been within the horizontal arrow range.

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You can see some of this on the G6 app. Look at the reading that appears on the main screen. Wait for the next point to appear, rotate the screen and look at the value for the 1st point. In many (most) cases, it will be 1-2 points different than when it originally appeared. It appears to be a simple smoothing function. The variation is very minor.