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Libre 2 Sensor Accuracy
- Thread starter Eternal422
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Eternal422
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That’s annoying. I think I’ve seen someone on this forum mention placing one on their chest I think? I’m sure someone will comment on what they’ve tried other than back of upper arms.
Eternal422
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Great new on my replacement sensor from Abbott - it lasted the whole 14 days and stayed really close to BG throughout! So pleased it worked and gave me some really useful data to help me adjust my insulin and get better control.
Now onto my third sensor and from the start it is pretty close to BG, and when BG is totally flat the sensor reads pretty much the same, so really happy with that! I now feel confident to base dosing decisions on its readings. Hoping this sensor lasts the course!
Now onto my third sensor and from the start it is pretty close to BG, and when BG is totally flat the sensor reads pretty much the same, so really happy with that! I now feel confident to base dosing decisions on its readings. Hoping this sensor lasts the course!
Proud to be erratic
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When I wasn't needing to comply with DVLA remit I wore mine on my chest, which was fine. I was happy to just use FP for driving requirements.
With readings at 2.4 below FP, I'd ask Abbott for a replacement - that much differential below makes the sensor unfit for purpose in terms of hypo alarms. I've muddled along with sensors reading up to 3 above FP, because the high alarm isn't important to me and I can set the alarm a bit higher should I feel it necessary.
I'm not finding the libre2 accurate at all. Regularly underreads by 2 to 5mmol.
I'm scratching my head to work out possible causes. it's been applied exactly as instructed.
next sensor goes on chest or stomach. it's accurate for about 8hrs on the arm. i probably sleep on it.
I'm scratching my head to work out possible causes. it's been applied exactly as instructed.
next sensor goes on chest or stomach. it's accurate for about 8hrs on the arm. i probably sleep on it.
@void what are your readings like and when did you apply it?
Are you aware of the known limitations of Libre that have been mentioned many times on this forum.
For example,
- any readings above about 9 and below about 4 are totally unreliable. If you are seeing extreme variations when your levels are above 12, I am not surprised.
- some of us find the sensor can take a day or two to bed in. If you are seeing extreme variations within 48 hours of applying the sensor, your body may be reacting to the alien object in your arm
- applying pressure to the sensor causes false lows. If you are seeing unreliable lows at night, this may be the reason.
Once we understand the limitations of the Libre system, many of us find it is a great tool. If these limitations are not understood, Libre feels like a complete waste.
Are you aware of the known limitations of Libre that have been mentioned many times on this forum.
For example,
- any readings above about 9 and below about 4 are totally unreliable. If you are seeing extreme variations when your levels are above 12, I am not surprised.
- some of us find the sensor can take a day or two to bed in. If you are seeing extreme variations within 48 hours of applying the sensor, your body may be reacting to the alien object in your arm
- applying pressure to the sensor causes false lows. If you are seeing unreliable lows at night, this may be the reason.
Once we understand the limitations of the Libre system, many of us find it is a great tool. If these limitations are not understood, Libre feels like a complete waste.
This one was applied 9 days ago. With this one, the first 48hrs were the most in agreement, after that, here's the last few readings where I also took a fingerprick test, 1st column sensor, 2nd one the meter. I don't think my body reacts to the meter as there's no soreness or itching, and it's acceptably accurate at that time.
| sensor | meter |
| 8.2 | 15.0 |
| 3.6 | 5.9 |
| 5.7 | 8.9 |
| 4.0 | 7.8 |
| 9.1 | 13.6 |
| 4.1 | 7.3 |
| 5.7 | 10.5 |
| 4.4 | 7.4 |
| 4.9 | 9.3 |
| 3.4 | 7.9 |
It wasn't mentioned in training. I am aware of the "lag" between fingerprick tests which test blood and are faster than the sensor that tests interstitial fluid. In training, a few minutes was mentioned, but I have seen some people report it can be a lot longer than that.
Proud to be erratic
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As I mentioned in an earlier response, once the sensor is below actual by c. 2.5 - and your readings clearly show this - it really isn't providing you with a reasonable degree of monitoring and certainly not giving you due warning when you are going low. With your sensor readings it's telling you that you are low when clearly not, so low alarms are useless and thus you can't anticipate forthcoming hypos. Also, your sensor to actual readings are very inconsistent; usually I would find my sensor to actual differentials were moderately constant, even if unacceptably big - when my BG was in steady state, ie a horizontal arrow. Even when I had vertical arrows, I can't recall differentials as great as a couple of your figures show; eg 8.2 to 15.0, 9.1 to 13.6 or 5.7 to 10.5.
The lag used to be declared as up to 15 mins for Libre 1, but claimed by Abbott as improved to 2.4 mins for Libre 2. I find it nearer to 5 mins. Knowing that delay exists, stops me from overreacting when Libre shows approaching 4 and I've already taken some response carbs. I can do this because I have my low alarm set for 5.6 and once I get that warning I monitor (ie flash scan) frequently and am ready to start snacking if it drops below 5.
I'd struggle to determine much from your sensor readings and would have replaced the sensor before 9 days - seeking a replacement from Abbott. If my crystal ball was working well I might have anticipated that a replacement was going to be needed and fitted a new sensor very early - prepared to wear 2 sensors while the new one 'bedded in' for more than a day. I would only start (activate) the new sensor once I've finally given up on the errant sensor, which could sometimes mean 3 or even more days wearing 2 sensors.
But, for me, a sensor has become unfit for purpose if I have to finger prick every time I scanned (because I'd lost confidence in the scan reading - evidenced by figures like yours) or unfit because the sensor low alarm, in particular, wasn't giving me due warning of my true BG falling - before I actually became hypo.
yeah I thought maybe it's just me, let it stablise. Out of the six sensors I've had, four have been returned due to this issue. That's why it's not gone back yet. I thought there was a limit on replacement. It's the weekend now, and Abbot won't be there. I'll try on Monday to get this one replaced.
nonethewiser
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Consultant once said to me that libre won't work for everyone for whatever reason no idea.
Those readings posted are way out & can see why your puzzled with results & cause, would be myself.
Tbh find libre 2 very accurate compared to 1 & hardly had any issues with it, wish I could offer some advice mate.
Eternal422
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Just an update on my experiences having read about other’s on this thread. Only on my 4th sensor, but this one is doing well as the others have (apart from my very first sensor which read low then failed after 8 days and my 3rd sensor that read low on its last day).
I know that there are so many variables and people’s experiences will be different, but just in case it helps anyone I have a good example here which hopefully goes some way to explaining differences between BG and sensor readings. This morning I got a sensor reading of 7.7 with rising fast trend arrow. BG was 5.8, but then just 10 minutes later sensor read 6. So just possibly I had a fast rising spike which subsided, meaning the sensor would be lagging behind as the BG fell (and hence reading higher than BG). This may explain some of the differences between Libre and BG that we all experience.
It’s taken me a month of using Libre, but I’m now trusting it and not continually comparing against BG. For me, doing this would make me continually doubt it and worry too much making it not worthwhile for me. However, trusting the readings (unless they do not match how I feel) I have been going along ok and bolus according to the sensor readings without any issues. Of course, my HbA1C will be the final judge of everything, I will get the result next week which will only include 1 month of Libre use but will be a starting point.
On a side note I have just started using the bolus calculation detailed in the “Think like a Pancreas” book, I.e. taking into account correction, trend and insulin on board. So far so good, but wouldn’t it be nice if the Libre app had this built in which would save me having to enter figures on a spreadsheet on my phone to derive a bolus figure then back into the Libre app to record it?
I know that there are so many variables and people’s experiences will be different, but just in case it helps anyone I have a good example here which hopefully goes some way to explaining differences between BG and sensor readings. This morning I got a sensor reading of 7.7 with rising fast trend arrow. BG was 5.8, but then just 10 minutes later sensor read 6. So just possibly I had a fast rising spike which subsided, meaning the sensor would be lagging behind as the BG fell (and hence reading higher than BG). This may explain some of the differences between Libre and BG that we all experience.
It’s taken me a month of using Libre, but I’m now trusting it and not continually comparing against BG. For me, doing this would make me continually doubt it and worry too much making it not worthwhile for me. However, trusting the readings (unless they do not match how I feel) I have been going along ok and bolus according to the sensor readings without any issues. Of course, my HbA1C will be the final judge of everything, I will get the result next week which will only include 1 month of Libre use but will be a starting point.
On a side note I have just started using the bolus calculation detailed in the “Think like a Pancreas” book, I.e. taking into account correction, trend and insulin on board. So far so good, but wouldn’t it be nice if the Libre app had this built in which would save me having to enter figures on a spreadsheet on my phone to derive a bolus figure then back into the Libre app to record it?
Paul Goldie
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Just out of curiosity I have been searching the Freestyle Libre 2 FAQs and web pages to see if they advise what would be classed as an acceptable tolerance between sensor and meter readings but can't see anything. does anyone know if there is one? Thanks.
Eternal422
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I have seen a figure on the Abbott website of 11.4% MARD (Mean Average Relative Difference) against finger prick tests. So I gather this means that the Libre reading could be +/- 11.4% of the finger prick reading. https://freestylediabetes.co.uk/freestyle-thinking/post/accuracy
The one I (was) wearing (up till waking up this morning) stopped with "the sensor has ended" I think this one had 8 days to go. This mornings real glucose was 4.8.
nonethewiser
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Good stuff, I've worn sensor on chest with great results, hope it continues for you.
harbottle
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I've used about 5 of these sensors, and have noticed with all of them:
- Initially (About half a day) they are always very high, but slowly drop down. (Starting by reading 8/9 when finger test reads 5/6)
- they are fairly close to finger prick tests (Using a contour Next) for around 7-10 days (Usually within 1, generally less.)
- after that they start to drift away quite a lot (Sensor reading > 7 when FP reads around 5.)
I tend to ignore the 'value' most of the time and just look at the trends and how different food affects me.
Placement seems important, as moving my arm and doing any sort of activity seems to cause major disruption with the readings.
- Initially (About half a day) they are always very high, but slowly drop down. (Starting by reading 8/9 when finger test reads 5/6)
- they are fairly close to finger prick tests (Using a contour Next) for around 7-10 days (Usually within 1, generally less.)
- after that they start to drift away quite a lot (Sensor reading > 7 when FP reads around 5.)
I tend to ignore the 'value' most of the time and just look at the trends and how different food affects me.
Placement seems important, as moving my arm and doing any sort of activity seems to cause major disruption with the readings.
Have you tried applying them half a day before activating? It is common for our bodies to take some time getting used to the alien object in our arm which affected the readings.
Maybe flex affects perfusion, maybe that's it.
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