Libre sensor activation time

Scott-C

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Hi all, have been using the libre for about 8 months now, love it for all the usual reasons.

I've been inserting it a while before activating it to give a bit of time for the local damage to settle down, certainly sorts out some of the first day eccentricities, so my thanks to the various posters who figured that tactic out - it's helped a lot.

What I wanted to ask, though, is, are people finding better accuracy based on the time or conditions in which they activate a new sensor?

I know that Dexcom/Medtronic gadgets are best calibrated when the user is running stable.

Libre, of course, is factory calibrated but as with Dexcom that didn't seem to me to mean much if I was to go start switching it on if I wasn't stable at the time.

So, for my last three sensors, I've made a point of activating it when I wake up, while I'm still in bed (I get "foot on floor" rise big time) on the basis that after a night sleeping, no bolus or food to speak of, that's the time when blood and interstitial are likely to be closest. Might as well give that wee disc the best start in it's short life!

Anyway, so that was the theory, and it seems to work for me. These last three sensors have been impressively accurate, to the point where after checking the accuracy with my normal number of bg tests over a few days, I've had days with one or two tests, and for the first time trusted the little plastic f***er enough to eat/bolus from it (don't drive so there's no dvla issues).

So, rambled on a bit, but there is a question tucked in there: have you noticed any difference in accuracy if the sensor is activated just after waking up after a stable night?
 

Snapsy

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Ooooh, not ever thought about how what's going on at the activation time might influence the accuracy, @Scott-C - that's a really interesting question! I start my new sensors usually around 7am on a Sunday, before getting out of bed, so I guess that fits with the circumstances you're talking about.

Speaking of accuracy, though, mine always reads higher than my blood does. It's so consistent though by the amount it's out by that I figure the issue is with the reader rather than the sensors.

That's really not a problem though, as I live my life by the shape of the line and the direction of the arrows - and it's a brilliant piece of kit!

Am sticking around to see what others say in answer to your question.

:)
 

AndBreathe

Master
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That's an interesting theory I hadn't heard before.
 
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Scott-C

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mine always reads higher than my blood does.

That's one of the puzzles, @Snapsy , that's one the puzzles!

Mine tend to read lower (accounting for lag) but consistently so, so it's a bit of head calibration. Only one of them has read higher, which took a bit of getting used to.

These wee things have really changed my approach to T1. I've sometimes felt like it's a constant war against hostile forces, but now I'm seeing it more as my beta cells accidentally got a bit of a kicking from my defence mechanisms, maybe it was friendly fire, maybe things just got out of hand when the defence cells were having their version of a Friday night out, so I'll say RIP for the betas, pick up what they were doing with some libre/strip assistance, give the defence cells a bit of a row, tell them, "you guys screwed up back there", but still say, ok, you're still doing some nice work for me. Bits of my body have fallen out with each other but I don't think any of them meant deliberate harm to me - I can live with that.
 
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CherryAA

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I have very stable blood sugars in the evening. since I started activating my sensor in tje evening. I have found the transition from one to the next to be very consistent in terms of the readings being exactly what I would expect. I uses to.activate them much earlier and I did have a lot more consistency issues. I had not connected the dots until you mentioned it
So thank.you
 
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I have just returned a faulty sensor and fitted a new one. As a result of this thread I will activate it tomorrow morning to see if it helps. The last one has gone back in a bio hazard bag.
 
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Books1

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LADA
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Insulin
Great thread thanks all - activating this am so will be interested to see what happens.
 

Mbaker

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Some goòd things said, but I have concerns with accuracy compared to One touch Select Plus; morning readings were evenly matched, but during the coarse of the day, I would often have to cross check, only to find my Libre was out significantly. It might just be my particular makeup, but I would urge caution if relying on the readings to make medication decisions.
 

Brunneria

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I'm completely open to this idea (I always start a new sensor when I am stable, because I do it sitting at my desk while working, usually for extended periods).

- and my sensors always seem fairly accurate - more so than a lot of the comments made on threads here. I have never needed to return one, which seems extraordinarily lucky, when I read other peoples' experiences.

But can anyone offer an explanation as to why this 'steady when activating' may be effective? Enquiringly mind wants to know! :D
 
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But can anyone offer an explanation as to why this 'steady when activating' may be effective? Enquiringly mind wants to know! :D

No, I can't see any logic in it at all but that doesn't mean it's not worth trying. After all, I don't understand how the sensor works at all so I can't knock a potentially useful idea.
 

Scott-C

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2,474
Type of diabetes
Type 1
But can anyone offer an explanation as to why this 'steady when activating' may be effective?

No, I can't see any logic in it at all but that doesn't mean it's not worth trying. After all, I don't understand how the sensor works at all so I can't knock a potentially useful idea.

I decided to try it after reading this article which explains a lot, even though most of it is way above my O grade and Higher chemistry!
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2903977/

Here's why it's a good idea to wait for a while before activating:

"Despite the advances in the making of sensors with new and improved designs and materials, sensor insertion causes trauma to the insertion site. It can disrupt the tissue structure, provoking an inflammatory reaction that can consume glucose followed by a repair process. The interaction of the sensor with the traumatized microenvironment warrants the need for a waiting period for the sensor signal to stabilize, and that period varies depending on the sensor type."
That explains why people complain of low readings in the first dayif they activate just after insertion: the wounded cells, repair cells and defence mechanisms which come along to attack the sensor as a foreign body eat up glucose around the sensor so the sensor is accurately reporting low glucose in that area even though glucose elsewhere is fine.

And here is why starting it while stable matters:

"Such calibrations transforms the sensor signal into a glucose value and assumes that the plasma-to-IF glucose gradient remains relatively constant. This assumption will not be valid if sensors are calibrated during rapid changes in plasma glucose, which is a major source of sensor error."
It just seemed to me to make sense that the "plasma-to-IF glucose gradient" was likely to be closest when I'd been sleeping all night with no food/bolus, stress, steady heart rate. The gradual seepage of glucose from blood to IF would be most likely to have balanced out, so if we're asking the sensor to make guess about what BG is, why not start when the two are most closely aligned.

After all, I don't understand how the sensor works at all

Next time you take a sensor out, have a close look at the filament. There's some black stuff on it and some metal. The black stuff is an enzyme, glucose oxidase,which breaks passing glucose down into other chemicals. When the glucose breaks down, it gives off electrons. That's basically the same as an electric current, which the metal bit picks up.The more glucose there is to break down, the more current there is, so the computing bit does some sums and says with this much current, my guess is that there's this much glucose. It's not measuring the glucose as such: it's measuring the current, and inferring what the glucose is. When I first read about this, my first thought was that it's extraordinary that we get any useful reading at all, so I've not got a lot of patience for people who say, ooh,it's not the same as my meter!

When I was a kid, I wanted to be an "inventor" (look, dad, I've built a robot!), didn't work out that way, but I've always been curious about things (especially when I'm forking out a hundred quid a month for them!), so I picked up a cheap copy of this book off Amazon: https://www.amazon.co.uk/Vivo-Glucose-Sensing-Chemical-Analysis/dp/0470112964

It gives a full history of glucose sensing with a focus on cgm for the people who develop them. Highly technical and way beyond me, but it's deeply impressed me with the way developers are dealing with some incredibly complex problems. It starts off by mentioning the Ebers papyrus from, get this, 1550 BC, which is (disputed) as being the first analysis of diabetes. So, it can't all be blamed onn the eatwell plate! Brief reference to "water tasters" - a guy must have had some bad karma in his life to get that job!


 
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@Scott-C. When just waking is about liver dump time shortly preceding breakfast. The sensor takes an hour ruminating before it is available for use. I assume that if any calibration happens then it happens during this time but are glucose levels really stable at this time?
 

Scott-C

Well-Known Member
Messages
2,474
Type of diabetes
Type 1
@Scott-C. When just waking is about liver dump time shortly preceding breakfast. The sensor takes an hour ruminating before it is available for use. I assume that if any calibration happens then it happens during this time but are glucose levels really stable at this time?

It depends on the individual. I chose the mornings because I've been lucky enough to have never really had Dawn Phenomenon in the sense of rises around 4am to 7am, but do get a fair rise just by getting up, so starting before I got up made sense for me. If others are not stable at that time, I suppose they might want to think about other times when they are stable. Actually, that bit you mention about the hour start up has got me thinking. I'm not sure what it's actually doing in that hour - is it measuring but not reporting, is it just rubbing the sleepy dust out of it's eyes? Good argument for staying in bed for another hour!
 

Scott-C

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Messages
2,474
Type of diabetes
Type 1
The waking rise has often puzzled me. There's such a sudden and prominent spike on the libre graph, a sharp tick up much quicker than the blood/IF lag that I'm not convinced it's a liver dump, at least not in my case. Liver presumably dumps into the bloodstream and that would then take time before it shows in the IF, whereas the libre graph uptick shows way sooner, usually. Maybe it's just that the fluid has been relatively static while resting and getting up just moves it around more? Maybe my geek book referred to above will provide some answers!
 
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6,107
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I have a cunning plan. I wake a few times during the night and the last time is usually when my Garfield trained cat decides he wants food. Overnight is a stable time for me usually so when the cat begins to cut up rough I will start it up and stay in bed. I love it when a plan comes together.
 

CherryAA

Well-Known Member
Messages
2,171
Type of diabetes
Type 2
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Diet only
@Scott-C. When just waking is about liver dump time shortly preceding breakfast. The sensor takes an hour ruminating before it is available for use. I assume that if any calibration happens then it happens during this time but are glucose levels really stable at this time?

I have chosen to do mine in the evenings becasue of this. My liver dump cause smuch more sever fluctuations early in the morning. If I truly wanted " stable" the best time for me would be around 1.00 am and five hours after any food.
 

Scott-C

Well-Known Member
Messages
2,474
Type of diabetes
Type 1
I have very stable blood sugars in the evening. since I started activating my sensor in tje evening. I have found the transition from one to the next to be very consistent in terms of the readings being exactly what I would expect. I uses to.activate them much earlier and I did have a lot more consistency issues. I had not connected the dots until you mentioned it
So thank.you

Cheers, Cherry, that's clear proof of my theory, but I know I'll not get a Nobel prize anytime soon (just kidding)!

I've always taken my T1D pretty seriously, because I have no intention of going blind or having stuff amputated, but I've never let it rule my life.

I know the rules, play by them, but really didn't bother exploring what was happening in the D community. That all changed after going on a DAFNE course, which inspired me to get a libre.

There's some people doing astonishing things out there: Abbott says not to wait before activating, yet some random internet punters show it's better to do so, hackers have hacked sony smartwatches and built their own transmitters to turn libre into a cgm, guys have tentatively figured out HDV to make insulin go find the liver, smart insulin which switches on and off depending on glucose levels, and wrapping beta cells in seaweed!

I'm a bit of a cynic, I know there's not going to be a cure any time soon, but when I see the sheer ingenuity of what people are doing for us, I am optimistic about the future.
 

CherryAA

Well-Known Member
Messages
2,171
Type of diabetes
Type 2
Treatment type
Diet only
It seems that there is skill out there to do amazing things with practically all technology, one lady on here had her husband connect a sytsem to Aleksa so it told her when changes were afoot.

I do find the libre is very useful as a built in will power angel !
you can't trick it !
 

Tubzi

Well-Known Member
Messages
55
Type of diabetes
Type 1
A bit late to this thread but...

How long before activating the sensor would you recommend actually putting it on your arm to allow the damage round the insertion site to repair?

Ive been getting readings lower than my meter shows
 
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