Any purpose to calibrating in first 12 hours?

CGM newbie here is now on 3rd sensor. G6.

Definitely see what everyone’s talking about, with the first half day or so on a new sensor. The sensor reading goes all over the place with no rhyme or reason and several times the screen just refused to give me any number at all and calibration attempts just whacked the system out. The wackiest results shown below. In the first hour after the two-hour warmup, the system repeatedly alarmed about impending sever hypo continually although all my finger sticks showed me stable at 140, then when I tried to calibrate the the thing it just went offline. Then overnight crazy stuff happened too.

So, there’s little to no value to me in sensor readings for the first half day, and me trying to calibrate the sensor can’t be good because those readings have nothing to do with where the sensor will eventually settle out and will just confuse the Dexcom brains. Right? Lecture me if I’m wrong and I will learn!

BTW, about 12 hours in, everything did settle in


I calibrate a sensor when it reports false severe lows for a couple of hours. The main purpose is to get rid of the beeping every 30 minutes. Unfortunately this intervention invalidates the factory calibration. I then must check up on the sensor and calibrate until it earns my trust (typically on day 2).


I too tried to calibrate through the false severe low and I’m thinking that was my mistake because I invalidated the factory calibration.

In retrospect maybe I should’ve just turned off all alarms for the first 12 hours. I haven’t done that yet but I think it can be set up that way (maybe the impending severe hypo cannot be turned off?)

Correct. Severe alarm cannot be turned off.

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New sensors often give crazy readings for me in the first 24 hours. I too have not had success with calibrating within the first 24 hours. I read somewhere to insert a new sensor (without transmitter) the day prior to starting new sensor to allow it to get used to your body. I’ve been doing this and it’s helped quite a bit avoid the first 24 hour wonky readings. When I forget to insert a new sensor early and those crazy readings come, I often just turn my phone off and use finger sticks :slight_smile:

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I haven’t had much trouble during the first 24 hours, but I also don’t check the accuracy anymore. I just let the pump and sensor do it’s thing.
I did once try to calibrate while I was participating in a clinical trial and I wanted the numbers to be in-line. So I calibrated and than lost the sensor. I am guessing, it doesn’t like being messed with. So I have learned to let it ride and it comes in line. And yes, I was one who thought OMG if the number is off, the pump will give me the wrong amount of insulin. But I am almost a year into the IQ system and have had no problem. The system is amazing.
So maybe just take a deep breath and let it ride and see what happens?
One of the endocrinologist I work with in some trials (who also has type 1) has been very helpful in getting me to let go. And another psychologist who has gotten to that “good enough” state.

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As many have suggested, as soon as I start to get questionable readings from my sensor I put in a new sensor for anywhere from 24 to 36 hours before I start using it. I also leave the questionable one in. From what I can gather this is referred to as “soaking”. I put a used transmitter in the soaking sensor to cover it. Since I have been doing this, I no longer have to worry about the first 24 hours. I still calibrate the soaking sensor when I calibrate the one that is working on my body so no additional finger sticks are necessary.

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I don’t have too much trouble with it, first I learned, don’t calibrate more than once in the first few hours? I calibrate at the beginning only to get rid of those obnoxious very low numbers. Then the second day once in the morning and once in the evening. Usually it is pretty close by that evening and I am just finessing it at that point. I like it to be closest in numbers at around the 95-100 mark as that is when I most care about accuracy for dosing.

As I just started a new sensor a couple of days ago, it reminded me how much I like to restart my sensors, so much more accurate and less work. I might have to try soaking so the new ones start out better.

I pulled one G6 sensor after 8-12 hours and at least four excursions. The site oozed blood after pulling, so I figure the sensor wire had some contact with blood. Other times, day one calibrations have put the sensor close or on the money,

That helps some get a good start and not lose a day, It adds up over the year.

@jack16 Restarting is the best way to gain days lol, They not only work much better, but you can gain a pretty good back up supply.

They just aggravate me at the beginning because they will vary for several hours before they settle. I have plenty of extra days as I average 26 days plus on each one. I’m dreading when I get a new transmitter number! Hopefully by the time I do, someone figures out the way around it!


Jack16, although I now soak a new sensor, I restart my sensor as often as I can. My sensors last for anywhere from 3-6 weeks. As you can imagine I have accumulated a good supply of sensors.


I avoid calibrating. I also put new sensors in in the morning to hopefully get some of the false lows out of the way before I go to sleep. (Not always successful as I can still be getting false lows after 12 hours but not usually after 24.)
Calibrating when it’s (falsely) showing a very low blood sugar has caused me, I think, to lose a sensor or two. (Not sure what goes on, but it just seems to get confused and will keep on asking for a new calibration in 20 minutes only to ask for it again when those 20 minutes are up.)
I do sometimes calibrate when the sensor is steady and not too low but wrong by a significant amount. For example it might show 110 and steady when a finger stick shows 180. That kind of calibration doesn’t seem to mess things up and even seems to bring them back into accuracy. However, that situation doesn’t come up that often. When the sensor is wrong, it also seems to bounce around a bit and in that case I don’t calibrate.

Overtime I’ve learned that in general you don’t want to calibrate. The tough thing is the CGM lags behind blood readings so its not that its wrong is that the readings are not as fast as a finger prick to track changes. The CGM will use algorithm to try to account for that lag with some success.

Personally I went from doing 1 calibration every day or two to basically never. I’ve found that doing a calibration generally causes me to less accurate results over time.

I usually calibrate like normal during the first 12 hours. I find I have almost no issue after the first 6 hours. I like to calibrate at each meal and before bed.

Note: I am a Medtronic ambassador. My opinions are my own. They did not pay me to say nice things about Medtronic devices or the company. In fact, they do not pay me at all. OK, they sent me a shirt and a cup but even I am more expensive than that.

I was reading 100 points off after inserting last night. Alarms all night long. I do not like the G6.

It really unnerved me too, when I saw my third and last (!!! Only get 3 every 30 days) sensor go completely nutso with false alarms for the first 12 hours. But it settled down 12 hours later and then I get 9.5 days of good data.

I think Dexcom is in this tough place between FDA requiring total shutdown after 10 days with no chance of restarting a sensor, the technology not capable of returning good data for the first day it half day, yet still marketing it’s products as being “continuous” when us real T1s sorely miss losing most of a whole day of data on each required sensor change.

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Regarding “soaking”: my recent transmitter is one of the new “8Gxxxx” ones that are programmed to invalidate a sensor if they detect a restart attempt. It does this based on the data during the initial 2hr warm-up. If it doesn’t fit the “insertion trauma” profile, i.e., if it’s too smooth, it invalidates the sensor and throws a “No restarts allowed” error.

I’ve been concerned as to whether this test would also invalidate a legitimately new but pre-soaked sensor, rendering the pre-soak technique for ameliorating the first-day bugginess unusable. I actually called Dexcom to ask about this, but of course it’s not an officially approved technique, so they can’t say anything besides what the book says, that you should allow no more than 1/2 an hour after sensor insert before attaching the transmitter. He did suggest that if your sensor was invalidated for this reason they’d replace it, but I’m not sure that’s ironclad.

Anyway, I decided to try a presoak as an experiment. I only gave it 12 hours, because in the past that has been sufficient to make a difference, though I confess I haven’t done the presoak thing too often because for various reasons it hasn’t been convenient at the time when the sensor change requirement is immanent. Result in this case was that I didn’t get the invalidation message (yay!), but it also didn’t have much effect on my BG track (boo!), which was too erratic to be much use for almost exactly 12 hrs before it settled down (kinda wondering if there’s something magical about that time period, it’s so suspiciously exact).

I’m due for another change tomorrow and my intention is to give a longer pre-soak a try and see what happens. May post a separate thread on the results.


Thanks for testing this out. After reading your initial post concerning this I opted to skip my soak when I used this new transmitter. I had started the new transmitter and sensor around 9pm and when i woke up the next morning around 5am calibrated and so far no issues
(that was Sunday nite/Monday morning). I did get one low alert over the first night.

Awaiting what you find out. I too had called Dexcom Tech support but unfortunately got someone who was clueless and clearly overseas.

I spoke with Dexcom’s regional manager last Thursday. He didn’t know whether the new algorithm would prevent presoaking. He was aware users were presoaking, but was under the impression most were doing it for only 2-3 hours. My personal experience so far is I need minimum 6 hours. That works most of the time but still not enough time for some sensors.

Anxiously awaiting @DrBB’s next report!

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