Calibrate, Why or Why Not

Currently I have a G5 but I will be getting a G6 next supply.

Why is it that we are not supposed to calibrate unless arrows are flat (stable)? I know there is a 10-15 minutes time lag. Is it because if it is in a climb or fall it is likely already higher or lower and therefore is already giving you inaccurate readings?

If my CGM indicates 100 and my Contour Next indicates 130 I would tend to calibrate to make it closer.

And if I waited for 15 minutes for it to stabilize, it is likely to go even higher.

I would also calibrate if my CGM indicates 100 and my Contour Next indicates 70 as that would also make it closer. But I would run AFAP (Fast) to the fridge.

So, I am trying to understand the logical, scientific, real reasons why you should wait for the arrow to be stable. NOT looking for because Dexcom guide says that on page xx.

It’s all about reducing variables.

When you have anything other than a flat, pointing to the right arrow, the relatively rapid changing of your BG is going to dramatically increase the chance of having an error in either your fingerstick or the Dex or both!

FWIW, 15 minutes is only 3 Dex readings. As just one example, today my BG was 157 with an arrow pointing up and to the right, while I was looking at it, a five minute window passed and it was 157 with a flat arrow to the right. Five minutes later, it was 153 with a flat arrow pointing to the right. When I first looked at the Dex, I was a bit concerned, but 11 minutes later I wasn’t.

With regard to calibration on the G6, I have recently been doing a fasting fingerstick, and calibrating based on that IF I feel it’s necessary.

I’m doing it this way because my BG is likely to be it’s most stable when I wake up. I am finding this to be really helpful and I will calibrate even if I’m off by 10 - 15%. The vast majority of the time, I don’t have to calibrate. The last two sensors I only calibrated once for each 10-day session.

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Why does it dramatically increase the chance?

Your example is perfectly valid, but I would assume that if your blood glucose is going up, it is more likely to continue to go up than become stable or stop in 15 minutes.

I would think it might be valid to not calibrate if the readings are very close even though you have a warning to calibrate but don’t know if that’s true.

Well, I don’t truly trust the CGM yet and hope the G6 is more accurate. I have heard about the same to much better. So far I haven’t heard the G6 is less accurate so I am hopeful.

Just as a f’rinstance, dunno if it helps, but I did a G6 restart two days ago, and when it came out of warm up the number seemed high. Even with restarts, the first couple hours can be a bit wonky. So I checked and sure enough Dex was about 35 points above fingerstick. So I did a calibration, and the reading came down match the fingerstick and has been within 10pts since. Not the first time I’ve had this same scenario play out this way, so that’s one of the times I go ahead and calibrate. Seems to help rather than hurt.

ETA With a genuinely new sensor I try to hold off through the wonky period but when it’s really zig-zagging I find it hard not to want to intervene and shake some sense into it.


So the G6 can be inaccurate on a restart, I mean more than usual? When I restart the G5, I don’t see inaccuracies such as in the first 24 hours when I first put the sensor in.

It does seem to be a thing with the G6, yes. It’s actually resulting from a feature in the algorithm that’s trying to account for the “initial trauma” of the insertion. The G5 AFAIK didn’t try to make that calculation and it also didn’t have the problem. So go figure. If you want to follow down this rabbit hole, search on “pre-soak,” a technique a lot of us use to minimize this.

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I am a firm believer in pre-soak at least for me. But I heard it is not as effective on the G6. I guess I will probably find out for myself.

Not sure I understand. Do you meant the G6 algorithm results in G6 not being as effective when restarting. I have heard this. What is the “rabbit hole” you are referring to?

It dramatically increases the chance because there are more things going on in your body - BG going up because you are still converting calories into glucose that maybe hasn’t reached your fingertips/interstitial fluid, or BG going down as insulin/activity/metabolism is still in play. Therefore, the odds of fingersticking alone giving you consistent, actionable info is at risk, so how can you utilize that as a calibration device?

My example was just to demonstrate that 15 minutes isn’t much in the eyes of a Dex device.

I’ve completely given up on re-starts for one major reason, lipohypertrophy. By moving my Dex sites more frequently, I’ve been able to get more accurate readings and I have aided the Dex in getting to the full 10-day wear. I had 22 sensors that either failed on start-up, or failed to make the 10-day period over 3 months. Since adopting a “no restart and rotate” protocol, I have had two failures in four months.

Thanks. Good explanation. Good news on your sensors. We all have to figure out what’s right for us. Generally, my sensors work best the longer they are in, until they don’t. I think I had one failed sensor in 18 months and one that lasted into its sixth week (the extremes). We’ll see what the G6 has in store. I’ll have to stop myself from wanting to calibrate the G6. Is their harm in calibrating it.

There’s no harm in doing periodic calibrations, but it’s best to avoid a lot of them in a short period of time.

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Yeah, seems like they were trying to fix something that wasn’t broke. Also seems more pronounced over the last, dunno 8-12 months than when I first started with the G6. I never noticed it at first.

Just a way of saying the pre-soak discussions are ubiquitous and extensive. But if you’re already familiar, no need to go there.

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Yow, that’s a lot! Guess I have to be That Guy who weighs in and says I’ve always gotten the 10 days and beyond, and have only lost sensors due to problems with the inserter, which seems to have become something of a QC issue for Dexcom lately. But once they’re in and settled mine have all been good. But yeah, rotating is essential.

Yep, it was a lot, AND a lot of frustration when I was following all the Dex procedures. Some of the 22 were QC issues, some were because my abdomen was just worn out from sensors, some were due to a premature failure of a transmitter.

Dex stood behind their product at every turn, but wasn’t too helpful in coming up with a solution beyond sending replacements.

Same here.

I prefer restarted sensors as a rule. The last few sensors haven’t lasted quite as long. Plus I have gotten more abnormal numbers after restarts than I used to. This last sensor the restarts were wildly off at first.

My restarts are always WILDLY off at first after a restart, by 100+ mg/dl. Have yet to see a problem after the first calibration, though. Which, by the way is exactly why I calibrate. I also find a big difference between 65 and 75, so will calibrate even for those small differences if it means the difference between my pump taking corrective action or not.

Well, they used to be off, but more like 35-45 points. But the last couple have been off by about 80 points. I hate that, it messes up my nice TIR numbers lol…so I calibrate them pretty quickly but they have reacted to that big of a correction by wanting another 1 or 2 calibrations. I don’t really remember getting that except maybe once before.

I am wondering if it’s this transmitter now or something they are doing to the sensors.

I went from G4 to G6. I was always calibrating my G4. I didn’t trust it at all. I really used it for grands to see patterns on the reports.
But I had a major wow moment when I was talking with some doctors at a meeting. And the reality is no equipment is full prove. I mean back in the day we took manual blood testing strips as gossip or further back we used urine testing to make judgements on insulin dosing.
So with the G6, I did just like the training says, let it go. So first, I don’t test. Like, I don’t test! It is liberating! I was super concerned that with my sensitivity, basal rates and carb ratios, if it was off I could get into a world of hurt. Over a year using the G6 with the Tandem Basal IQ, I have had no major issues! No emergencies, no paramedics called, no one having to help me with lows. Pretty sweet. My time in range has improved, my a1c has stayed the same. It is all good.
Now, I do believe that I am very blessed. Most of the general info works for me. I can follow most guidelines and be fine. I don’t have side effects to most drugs. I just follow the guidelines and things go pretty mich like they should.
But I will say I calibrated once in the past 2 weeks and that was because I was doing a long day clinical trial, and it was off compared to the lab numbers, so we calibrated to make it easier for the medical professionals to see what was going on. And even with the calibration, it took awhile for the numbers to come in line. So most times when I do calibrate, I know it will eventually catch up.
Sometimes when you calibrate too much, it can really mess thing up. So my mantra now is, Let it ride and see what happens.

Do not calibrate during rapid rise or fall because it will mis-calibrate. It will attempt to match your number to something inaccurate. Does that makes sense?

Calibrating a G6 will do next to nothing, unless your running in a mode that requires calibration.

People do see large inaccuracies in G6 that tend to happen throughout a 90 day supply, so you always double check.

I believe you’ve said that before, and it’s absolutely not true. I don’t know why you think that. You can indeed calibrate a G6 and have it matter…

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