How long should I give an inaccurate CGM sensor?

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Vectian

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I started a new Libre 2 sensor Sunday night as usual so that it would start overnight on regular BS. I had put the new one on in the morning so it had all day to adjust. The readings have been way above actual, 2 or more higher checked with fingerprint and against the previous days on the old sensor. This is very annoying as it has messed up all my averages and time in target! You can't tell it to disregard faulty data.

New sensors always read too high for me in the first couple of days then settle down, but not usually this far above. How long should
I give it before replacing?
 
Sorry to hear you are experiencing problems. Are you well hydrated as that can cause higher interstitial readings. Are you double checking the Libre readings when your levels are stable and in range? It is common for Libre to read higher than BG when you are above range. I tend to just do a couple of checks on the first day or two of a new sensor when I am mid range 5 or 6mmols and have been fairly stable in that range for at least half an hour.
If you are finding the first couple of days are always erratic, then maybe apply the sensor 2 days before you intend to start it.
If you have 3x in range readings where Libre is more than 2mmols out from finger pricks taken at the same time, then report it to Abbott and they should replace it.

If you have lots of problems with Libre being inaccurate, then it may be worth asking to try the Dexcom One sensors instead, because some people find Dexcom suits their body chemistry better than Libre and vice versa.
 
rebrascora said:
Sorry to hear you are experiencing problems. Are you well hydrated as that can cause higher interstitial readings. Are you double checking the Libre readings when your levels are stable and in range? It is common for Libre to read higher than BG when you are above range. I tend to just do a couple of checks on the first day or two of a new sensor when I am mid range 5 or 6mmols and have been fairly stable in that range for at least half an hour.
If you are finding the first couple of days are always erratic, then maybe apply the sensor 2 days before you intend to start it.
If you have 3x in range readings where Libre is more than 2mmols out from finger pricks taken at the same time, then report it to Abbott and they should replace it.

If you have lots of problems with Libre being inaccurate, then it may be worth asking to try the Dexcom One sensors instead, because some people find Dexcom suits their body chemistry better than Libre and vice versa.
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It always reads too high on the first few days of a new sensor, then drops down to the right level for the rest of the 14 days. I usually drink 2l of water a day, and the previous day's readings would also be affected, it's only when changing the sensor. You can see very clearly on the graph that it all sits quite a bit higher immediately after changing.

I try and avoid putting a new sensor on days before, because then I would have to sleep with one on each arm. It's already uncomfortable trying to avoid sleeping pressing on the sensor on one side, both would be too disruptive.

I am very rarely above 10 (in reality, as opposed to incorrect readings) and then only slightly for a short time so yes all double checked readings are below that. It's frustrating because you can't delete data you know is wrong from a faulty sensor, so looks like your control is worse when it isn't and I have worked really hard to keep it in a good range.
 
I understand it is annoying having your stats trashed, but try to remember that Libre is there to help you not for clinician to judge you. As long as you can explain the issue and your results are still reasonably good then it doesn't matter if you are 2mmols high for a day or two.

It does sound like you are having a strong insertion trauma response.... ie your body is having a significant reaction to the filament and perhaps introducer needle being inserted into the tissue. It may be a coating on the needle or filament which is causing this reaction and it is possible that a different system like Dexcom, uses different coatings that you might not react to, so worth trying the Dexcom One Plus. I think they were offering a free trial recently. It was somewhat short lived due to demand, but I think you can still ring up and ask and if you explain your circumstances they will likely send you one to try. Of course it will be important to ensure you have a compatible phone first. I think the Dexcom can also be used elsewhere on the body which you might find more comfortable.
 
Inka said:
Just ignore the dodgy Libre data @Vectian It doesn’t count because you know it’s inaccurate. I’d leave the sensor until tomorrow personally as that’s not hideously out for a Libre.
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I may have to bin this sensor, the entire graph is sitting 2mmol too high so something has not gone right with this one. I don't know if it hits muscle or bone or something when it's inserted it messes up the calibration. They are always too high on the first few days, but not so much as this.
 
rebrascora said:
I understand it is annoying having your stats trashed, but try to remember that Libre is there to help you not for clinician to judge you. As long as you can explain the issue and your results are still reasonably good then it doesn't matter if you are 2mmols high for a day or two.

It does sound like you are having a strong insertion trauma response.... ie your body is having a significant reaction to the filament and perhaps introducer needle being inserted into the tissue. It may be a coating on the needle or filament which is causing this reaction and it is possible that a different system like Dexcom, uses different coatings that you might not react to, so worth trying the Dexcom One Plus. I think they were offering a free trial recently. It was somewhat short lived due to demand, but I think you can still ring up and ask and if you explain your circumstances they will likely send you one to try. Of course it will be important to ensure you have a compatible phone first. I think the Dexcom can also be used elsewhere on the body which you might find more comfortable.
Click to expand...
I didn't know that insertion trauma was a thing, with such a small needle. It would make sense why it's raised just after inserting and maybe when the "wound" has calmed down a bit in a few days it calibrates better. Sometimes there is dried blood on it when I take the old one off, and sometimes it makes the whole area quite sore for a while after inserting.

Quite a bit of clinician judging going on, they don't believe that I can control it with diet and exercise alone, despite proving them wrong and having an A1C of 36, so don't want to give them any "I told you so" material. Just tested again, CGM says 7.6 and it's 5.6 think I will have to bin this sensor.
 
If your BMI is below 25 the FSL won't be reliable, most times it will start high and end low, but it could also be the other way around. The MARD at a BMI of 21,6 is more than twice as high than that at a BMI of 25,6.
 
Bubbleblower said:
If your BMI is below 25 the FSL won't be reliable, most times it will start high and end low, but it could also be the other way around. The MARD at a BMI of 21,6 is more than twice as high than that at a BMI of 25,6.
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Ah didn't know that, my BMI is 21.7. Some new acronyms for me! FSL? MARD?
 
From https://www.freestyle.abbott/eg-en/...q=the-freestyle-libre-system-tab-question-109
The MARD (Mean Absolute Relative Difference) measures the average difference between a device measurement (or test result) and the reference measurement at normal to high glucose levels.​

FSL is just an initialism for FreeStyle Libre. (FGM also used to be used for Flash Glucose Monitor, but it wasn't a great initialism then and CGM is better now anyway.)
 
Bubbleblower said:
If your BMI is below 25 the FSL won't be reliable, most times it will start high and end low, but it could also be the other way around. The MARD at a BMI of 21,6 is more than twice as high than that at a BMI of 25,6.
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Where does that information come from, please? I’ve never heard of it before. I generally find mine accurate for the whole life, and my BMI is 21.
 
Robin said:
Where does that information come from, please? I’ve never heard of it before. I generally find mine accurate for the whole life, and my BMI is 21.
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Neither have I ever heard of it - just used an online calculator which I believe is a USA one since I was required to enter my height - 5ft 1in - and weight - 9st 12 but in lbs so 138lbs and the answer was 26.1. 'Overweight' starts at 132 lbs - hence the Libre could not possibly ever be accurate for anyone at all anywhere in the world, who is not overweight.

That does NOT sound correct, to me!!
 
Robin said:
Where does that information come from, please? I’ve never heard of it before. I generally find mine accurate for the whole life, and my BMI is 21
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It was studied among Japanese non diabetics (by Abbott);

"Assessment of factors that determine the mean absolute relative difference in flash glucose monitoring with reference to plasma glucose levels in Japanese subjects without diabetes" (unfortunately the PDF is damaged now).

Multiple regression analyses revealed that BMI contributed the most to the MARD when FGM-SG and PG level were compared, as lean individuals have a greater MARD regardless of glucose levels.


You are luckier than me, my BMI is also 21 but my FSL is completely unreliable.
At first I never realised this, even when my HbA1c's were more than 33% from the estimated A1c, using the full 90 days, and I always double- and tripple checked with fingerpricks.
Only when my HbA1c suddenly shoot up another 25% while I was doing so perfectly according to my FSL (which predicted 38 mmol/l, while it was 62 mmol/l) I started realising this, that took me 3 years.
 
Satan’s little helper said:
The study is over 4 years old, by the date stamp.
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Too bad you can't actually read it.

You think in the last 4 years "lean individuals" suddenly no longer have a significantly (more than 100%) higher MARD?

It isn’t only BMI that determines this by the way, for example insulin resistance plays a large role too, the lower that is the higher the MARD. I hope you can somehow read this:

1727287078746.png
 
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The PDF works for me in Chrome, I've not read it yet, but it loads correctly: https://www.jstage.jst.go.jp/article/endocrj/67/5/67_EJ19-0488/_pdf/-char/en

My BMI is apparently 22.6, though I am lean and there are very few bits of the back of my arm that appear to have anything pinchable (my non-existent bingo wing location is the only game in town, which means changing a sensor early is a pain, literally, as the new one has to go back near the old site on the other arm), so perhaps that explains why my sensors are often not very well calibrated. Though it doesn't explain why Bluetooth fails on them quite often too!

Before taking the sensor off @Vectian you might try to generate a large and fast BG change, in order to make the sensor go offline and do (I assume) a recal. This sometimes makes my faulty sensors move closer to finger prick values. I see these swings by accident - usually when I go riding with persistently elevated BG, then it drops through the floor and goes offline.
 
Vectian said:
Just tested again, CGM says 7.6 and it's 5.6 think I will have to bin this sensor.
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Do give Abbott a call if the sensor isn’t performing as you’d expect @Vectian

They’ll almost certainly replace it for you.
 
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