Dexcom G6: how is the algorithm affected by calibrations, and why does it take so long to convince it that it's wrong?

Diabetes Technology
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I put the code in my BG meter case, that way I would basically have to lose my meter in order to lose the code. I agree with @Robyn_H , pre-soak your sensors and you just may not have to deal with this anymore but if you still do have issues then calibrate in steps.

I have found that if I have a sensor that is wildly off at start up then it wasn’t inserted quite right either from user error or the inserter flubbed it. When you remove the sensors that start off bad do you look at the wire? I have seen that the wire will be bent or skewed in the wrong direction and sometimes I will even have a bruise under the adhesive.

I think the accuracy of the G6 is dependent on the wire being in just the right place in your subcutaneous tissue. If it goes in too deep instead of just skimming the fatty layers it really throws it off.

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@schleima you’ve gotten so much good advice here; I just wanted to jump in for 2c worth… I consistently have this problem (like, every sensor – it’s crazy-making). The only thing that mitigates it is putting a new sensor on at least 12 hours before the old one runs out. So, when I get the “12 hours left” message on my phone, I put a new sensor on. I don’t put a dummy transmitter in or tape over it or anything. I just let it sit and it’s always been fine. Then I give it at least 12 hours to get used to my body and once it’s gone through the 2 hour warmup with the transmitter in (after the old sensor has finished), my readings are easily within 20% of finger sticks. Good luck! Jessica

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I tried pre-soaking for a few sensors and it does improve the accuracy for first 24 hours or so. But I gave up pre-soaking because (1) I was doing restarts and did not want to “waste” a day of sensor lifespan and then (2) With restarts, and with sensors that fail before 10 days, I was dealing with unpredicted new sensor start days/times. No time for a presoak unless still wearing a working sensor. I gave up on pre-soaks after that.

I have had great experiences with Dexcom replacing sensors that fail before 10 days. They ask for some details (lot number etc.) but seem pretty easy going about sending new sensors to replace any that fail before 10 days. “Fail” for me has meant sensors that totally die but it also means not reading within the stated level of accuracy. If you keep having accuracy/calibration trouble you should contact Dexcom and see what they say about replacing the sensor.

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schleima - I sympathize with your frustration that the Dexcom software has been programmed to not believe your calibration values when quite different from the most recent G6 reading.

It is natural to get frustrated – Dexcom could and should have done better. Blood Glucose meters using test strips have been refined to be quite accurate, and the software should just believe you. But it is what it is.

I mostly run into the problem you describe during the 1st 24 hours of a new sensor – not all the time, thankfully.

I appreciate the tricks people have described, basically to not shock the software with a calibration value that is hugely different from the most recent G6 value. It as if we need to be sure not to offend the persona in that software.

Since I am able to get fairly inexpensive test strips, and when my meter calibration value causes my receiver or app to reject my calibration and more or less shuts down, I just switch to depending on my meter for as long as it takes to convince the Dexcom software it is wrong and my meter is right. Sure, this might be 20 minutes or 2 hours, but I just will not let myself get frustrated, since the meter allows me to manage my glucose levels while Dexcom is down.

I am ok with all this because most of the time, my G6 is reasonably accurate, typically on days 2-10 of a new sensor. And having a good CGM like the G6 is so wonderful, that these occasional problems are ok with me.

I happen to use Medicare for insurance, and I find it strange that they will not pay for BG meter test strips when they fund the Dexcom G6. I could not use the G6, at least during the 1st 24 hours of a new sensor, without a BG meter. Luckily, I use a meter for which accurate 3rd-party affordable test strips are available, so I am quick to let the meter take over if the G6 software goes funny.

By the way, there are times the underlying problem is the sensor did not get installed correctly or the sensor wire has been pulled out, maybe while sleeping – in other words, sometimes, the software is right that something is wrong. In those cases, switching to a new sensor is probably the only solution.

These new technologies are so, so much better than what was available just 10 years ago, that I think we just need to tolerate the idiosyncrasies while enjoying the huge benefits.

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Good point.

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The fact that the sensor will revert to factory calibration is the reason it doesn’t need calibration. Or at least as far as the FDA is concerned.
There are so many factors that effect it,there is no way for dexcom to address them all.

Things like poor lymphatic circulation, people with scarred skin, or very lean people who have little room for the sensor wire.
There also is an issue of dexterity and consistency with insertion.

For me, it works very well most of the time, when it’s off, it’s generally a complete loss, when it’s good it’s pretty spot on

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I have been having this problem the last 4 times I have restarted my G6 sensor. I’m wondering if somehow they have programmed the sensors not to function after a restart. I have done the small step approach without any luck. Just keeps telling me to recalibrate after X time. I do but nothing changes.(I’m involved in this right now.)

Whenever I call Dexcom they just say they will send out a new one. They give NO feedback. They actually sound like some of these machines that we end up talking to anymore. I think next time I will try the suggestion to not enter a code number when starting. I would be happy to calibrate manually if that will work. I like the accuracy when things are working, but the days of insertion are getting very tiresome—not to mention 12-24 hours of inaccuracy.

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Re: customer service not giving any insight, yes this frustrates me to no end. They always send out a replacement; that’s not an issue. It’s that the agents are stuck on a script and don’t seem to have any real insights into how the product actually works under the hood.

Several years ago when I used the G4, I had the problem where multiple receiver speakers died. This ended up to be a manufacturer error and a big recall happened, but every agent I spoke with before the recall I had to go through the same tedious troubleshooting flowchart. Not one time did an agent acknowledge “this has been happening a lot-- I’ll get this taken care of for you.” It was the same robotic dance every time, and nobody acknowledged it wasn’t my fault.

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Think about what life must be like for someone that doesn’t want to take any risk of losing this customer service job. Have you ever been that dependent on keeping a job? What must that be like?

That’s the thought I try to keep in mind when I call the cust svc number. I hope it reminds me to be polite and patient and remember that the person I am talking to is powerless to actually change how the company treats me. :thinking:

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