Freestyle Sensors Reading too High!

[Tilly26]

Hi, I have recently come back to using sensors. Following a couple of serious Hypos I have been checking with my Accu Check Mobile fingerpricks & have discovered that the sensors are reading 2 units too hi. Has anyone else found this please? I am really struggling to get things on track.
Thank you!

 

[Eternal422]

I have found that all my sensors tend to read lower than BG, typically between 0.5 and 1 mmol/l lower, never higher. I presume you are allowing for the lag between BG and ISF readings? Also, if BG is dropping quickly then the Libre will read higher until it catches up with BG.

 

[Robin]

I have found that all my sensors tend to read lower than BG, typically between 0.5 and 1 mmol/l lower, never higher. I presume you are allowing for the lag between BG and ISF readings? Also, if BG is dropping quickly then the Libre will read higher until it catches up with BG.

I find quite often the opposite happens. The Libre algorithm that tries to catch up the gap by predicting where your BGs are currently, sometimes tells me I'm higher than I am, because it’s following the pattern of a rise that’s been happening over the course of the last couple of hours, and doesn’t spot that I’m levelling off. Swiping again 15 mins later sometimes shows me that the high reading has disappeared, and the curve has indeed levelled out. (The reverse is also true, a trip into hypo land following a downward trend, sometimes never appears on the daily graph)

 

[harbottle]

When I used Libres I found that there was a window when they were very close to finger pricks, but after around 8 days they started to drift upwards and could give me a reading that was around 3 higher than a finger prick (Finger prick would give 5, and libre was saying 8). I believe that after a while the fibre inserted into the skin gets 'fouled' and this starts to affect readings.

On the few occasions I did eat something carb-y I'd see a high reading, but that was maybe a guess, as when it had got all the readings over time there's be a rogue dot on the graph - usually happens when things are changing rapidly.

 

[helli]

@Tilly26 sorry to read about your hypos and your inaccurate Libre sensor.
What are your levels like when your sensor reads high? I ask because the difference is usually a percentage rather than an absolute number plus CGMs are designed to be most accurate at "normal" levels. Therefore, if you are finish it to be out by 2 mmol/l when your levels are over 10, that is different to if your levels are 2 mmol/l out at 5.
If it is the latter, I recommend contacting Abbott (with proof) and they are likely to replace your sensor.
If it is the former, my advice is to never trust CGMs over 10 and always check with a finger prick when you are at these levels.

 

[khskel]

Currentl showing 10.7 after breakfast. Fingerprick test 7.6. it'll level off in a bit.

 

[Tdm]

Yes, i had that with libre too, occasionally
If you want a replacement i think they ask for 3 readings showing a substantal difference when your blood sugars are level.
Readings are often odd with all monitors first 24 hrs.
Now on dexcom so i can calibrate. I beleive if you use 3rd party apps they allow you to calibrate libre.
When i was on libre i would adjust my alarms if i had a 'high reader' but if its very off you can't set your low alarm high enough

 

[rebrascora]

Like @Eternal422 I find Libre reads slightly lower than my BG meter in range, but if my levels are above range (in double figures) then Libre will usually over estimate. It is important to understand Libre's limitations and if you are going to compare it with a finger prick as a means of assessing it's accuracy for you, then choose a time when you are mid range and your levels are nice and stable. So I am going to do a check now because I have been in the mid 6s to low 7s for the last couple of hours.... so nice and stable. Current Libre reading is 6.8....BG 7.4 on my Caresens meter which I trust. 6.6 on a Libre Optium test strip, that go in my Libre reader and they always seem to read lower than the Caresens and Libre reader.
Those results are all really close enough though and I am very happy with them, but it is important to do that sort of check when your levels are stable and in range. If you are checking because your levels are too high or too low ie. above or below range, then the Libre is only a guide and you need to double check with a finger prick and take the finger prick result as being more accurate to work out corrections or hypo treatment. It is also important to check with a finger prick 15 mins after a hypo treatment because Libre will almost always show that your levels have continued to drop lower, when in fact that is just the algorithm in the app or reader and your finger prick will almost certainly show that your levels have come back up. If you rely solely on the Libre, then you can end up over treating a hypo and going too high afterwards.
Also important to know that if you apply pressure to your sensor like leaning against a wall or more likely lying on it in bed whilst you sleep, it will record a false low due to compression of the tissue under the sensor, when you roll over and release that pressure it will often rebound and go slightly higher than you actually are and then settle back down to where it should be, so do be wary of that.

Unfortunately all that said, there are some people whose body chemistry does not agree with Libre and it is less accurate for them than most of us find and it may be that an alternative system suits your body better, so you could discuss that with your nurse or doctor, but those systems will also have limitations like I have mentioned above, so it is important to understand that before considering a swap.

There are also unofficial apps that you can use and will allow you to calibrate your Libre if it is consistently out when your levels are mid range, so that might be an option to try and there are members here who would be able to advise you on that.... Personally I am a tech dinosaur, so it would be like the blind leading the blind for me to suggest one. 🙄

 

[Inka]

Hi, I have recently come back to using sensors. Following a couple of serious Hypos I have been checking with my Accu Check Mobile fingerpricks & have discovered that the sensors are reading 2 units too hi. Has anyone else found this please? I am really struggling to get things on track.
Thank you!

Yes, my last few Libre sensors were awful for that. They’d say I was 13 when I was 9, for example. Earlier sensors weren’t as bad so do check the batch numbers. As said, the Libre drifts in accuracy above and below the normal range. If in doubt, always fingerprick.

 

[Tilly26]

@Tilly26 sorry to read about your hypos and your inaccurate Libre sensor.
What are your levels like when your sensor reads high? I ask because the difference is usually a percentage rather than an absolute number plus CGMs are designed to be most accurate at "normal" levels. Therefore, if you are finish it to be out by 2 mmol/l when your levels are over 10, that is different to if your levels are 2 mmol/l out at 5.
If it is the latter, I recommend contacting Abbott (with proof) and they are likely to replace your sensor.
If it is the former, my advice is to never trust CGMs over 10 and always check with a finger prick when you are at these levels.

Hi thank you for your replies
. OK so the particular readings are :
Monday.
Sensor Reading 12.2
Finger pick. 10.4

Sunday.
Sensor Reading. 17.4
Finger Prick. 14.8.

This is a new sensor as I changed it after the discrepancy with the highest reading on Sunday.
So it is not a Sensor issue.
Nor is it a MP issue- I have changed back to a new monitor given the random high sugars.

I have also just discovered that ACCU check Mobile no longer provide the cassettes for testing - they only do individual strips.
Anysuggestions- ?
Thank you!

@Tilly26 sorry to read about your hypos and your inaccurate Libre sensor.
What are your levels like when your sensor reads high? I ask because the difference is usually a percentage rather than an absolute number plus CGMs are designed to be most accurate at "normal" levels. Therefore, if you are finish it to be out by 2 mmol/l when your levels are over 10, that is different to if your levels are 2 mmol/l out at 5.
If it is the latter, I recommend contacting Abbott (with proof) and they are likely to replace your sensor.
If it is the former, my advice is to never trust CGMs over 10 and always check with a finger prick when you are at these levels.

 

[Tilly26]

Yes, my last few Libre sensors were awful for that. They’d say I was 13 when I was 9, for example. Earlier sensors weren’t as bad so do check the batch numbers. As said, the Libre drifts in accuracy above and below the normal range. If in doubt, always fingerprick.

The trouble is if I have to check all the yine then it's pointless doing the cgm

 

[helli]

Unfortunately @Tilly26 as these numbers are all above 10, in my experience, I would take the sensor readings with a pinch of salt as they are not designed to accurately read levels this high. This is why the advice is always check highs (and lows) before making a correction.
You also mention this is a new sensor. Many of us find our body takes a while (up to 48 hours) to get used to an alien object inserted in our arm which can affect the readings from the sensor. This is why it is common to apply a sensor a day or two before activating it.

Libre (and other CGMs) are amazing pieces of kit but you do need to understand their limitations. Otherwise, they are just frustrations.

 

[Tilly26]

OK well I have a mixed experience with Libre which us why I stopped using them for the last 18months. I was purchasing them myself. However I stopped when I had the most appalling skin reaction.
I only started again last week ac my DNurse wanted to be able to see my readings .
I have also had appalling experiences with customer services at Abbott so would be happy to try something else!
I am having issues with high readings at the moment as I have an ongoing gynae issue & recurrent infection.
So things are pretty difficult at the moment.

 

[Robin]

The trouble is if I have to check all the yine then it's pointless doing the cgm

I think we all get hung up on accuracy because the decimal point makes us think that we are using a very precise instrument. In fact, blood glucose meters only have to give a reading within 10% of the true figure, so your first reading, 12.2 as against 10.4 could well be within the permitted tolerances for both devices, and be around 11.0. With the 17.4 one, did you scan again 15 minutes later to see if it had come down closer to your 14.8 fingerprick? It may have been a case of the Libre algorithm assuming that your blood glucose was going to co it ue rising, when in fact it was levelling off, as I explained in my post above.
I tend to think of readings at that level as 'too high, need to do something' rather than treating it with pinpoint accuracy. After all, I can’t correct with an insulin dose smaller than half a unit, which gives me some leeway as to where aim going to end up.

 

[Tilly26]

Yes, my last few Libre sensors were awful for that. They’d say I was 13 when I was 9, for example. Earlier sensors weren’t as bad so do check the batch numbers. As said, the Libre drifts in accuracy above and below the normal range. If in doubt, always fingerprick.

What are the festive finger prick monitors at the moment?

 

[Tilly26]

I think we all get hung up on accuracy because the decimal point makes us think that we are using a very precise instrument. In fact, blood glucose meters only have to give a reading within 10% of the true figure, so your first reading, 12.2 as against 10.4 could well be within the permitted tolerances for both devices, and be around 11.0. With the 17.4 one, did you scan again 15 minutes later to see if it had come down closer to your 14.8 fingerprick? It may have been a case of the Libre algorithm assuming that your blood glucose was going to co it ue rising, when in fact it was levelling off, as I explained in my post above.
I tend to think of readings at that level as 'too high, need to do something' rather than treating it with pinpoint accuracy. After all, I can’t correct with an insulin dose smaller than half a unit, which gives me some leeway as to where aim going to end up.

I think it is dangerous to work on the lea-way principle for someone who is sensitive to insulin for myself.
As I had not realised there was an issue I took the insulin on the sensor reading which resulted in a serious hypo.
From what I am reading it us a case of all ways doing a finger prick in that situation

 

[helli]

I think it is dangerous to work on the lea-way principle for someone who is sensitive to insulin for myself.

You have always been working on the "leaway approach" but maybe you were not aware.
Just like CGMs, finger prick monitors have an accuracy tolerance of 15%. There is no home blood glucose testing kit which is completely accurate.
We get used to accepting the meter accuracy and only question it when we have something else to compare it with.

If one meter reads 15% higher and another reads 15% lower, a true (completely accurate) reading of 10.0 could be shown as 11.5 on one meter and 8.5 on the other.

However, as CGMs are designed for accuracy at "normal" levels, they may be less accurate above 10 mmol/l (and below 4 mmol/l). Hence, the advice to always check the CGM reading when making a correction. If your levels are between 4 and 10, there is no reason to double check.

As for the tendency of Libre to drift over their life time, I take one finger prick reading every day when my levels are stable and in a normal range (usually when I go to bed) to check the Libre has not drifted too much.

 

[rebrascora]

What do you have your low alarm set at? Perhaps setting it a bit higher would give you more time to respond to an impending hypo and treat it.

When I do a correction, I always just work off my Libre reading these days on the understanding that it may be high. I then keep a close eye on my levels and have JBs ready so that if it gets to mid 5s with a vertical or slanting downward arrow, I will have 1 JB to steady it and then see how it goes from there.
How frequently do you scan Libre? The more often you scan, the better your understanding you get of how it works and how your body works. I scan about 30 times a day which you may consider excessive and I certainly don't do anything with much of that information but it gives me a really good insight into what is going on and how my body is responding and reassurance that my diabetes is behaving or a tip off that things are going haywire. If I can keep my levels in range (3.9-10) as much as possible my diabetes is much easier to manage. I proactively correct before I hit 10 to maintain that as much as possible, because that makes it easier and my Libre is more reliable at that level.

I appreciate that if you are unwell and suffering with infections then it will be tougher but I would encourage you to perhaps scan more often to get more familiar with your Libre and particularly after a correction to keep a close eye on how your levels are responding to prevent such nasty hypos happening again. No reason why you need to wait until you are hypo before you take action. The huge advantage of the alarms on Libre are that you can head them off before they get below 4.

 

[Tilly26]

What do you have your low alarm set at? Perhaps setting it a bit higher would give you more time to respond to an impending hypo and treat it.

When I do a correction, I always just work off my Libre reading these days on the understanding that it may be high. I then keep a close eye on my levels and have JBs ready so that if it gets to mid 5s with a vertical or slanting downward arrow, I will have 1 JB to steady it and then see how it goes from there.
How frequently do you scan Libre? The more often you scan, the better your understanding you get of how it works and how your body works. I scan about 30 times a day which you may consider excessive and I certainly don't do anything with much of that information but it gives me a really good insight into what is going on and how my body is responding and reassurance that my diabetes is behaving or a tip off that things are going haywire. If I can keep my levels in range (3.9-10) as much as possible my diabetes is much easier to manage. I proactively correct before I hit 10 to maintain that as much as possible, because that makes it easier and my Libre is more reliable at that level.

I appreciate that if you are unwell and suffering with infections then it will be tougher but I would encourage you to perhaps scan more often to get more familiar with your Libre and particularly after a correction to keep a close eye on how your levels are responding to prevent such nasty hypos happening again. No reason why you need to wait until you are hypo before you take action. The huge advantage of the alarms on Libre are that you can head them off before they get below 4.

Thanks Barbara, yes I do scan a lot so am aware of the trends. Unfortunately with my MPhone I wasn't getting alerts & I was needing to scan several times to get a reading. So have now set up with a new monitor.

 

[Tilly26]

What do you have your low alarm set at? Perhaps setting it a bit higher would give you more time to respond to an impending hypo and treat it.

When I do a correction, I always just work off my Libre reading these days on the understanding that it may be high. I then keep a close eye on my levels and have JBs ready so that if it gets to mid 5s with a vertical or slanting downward arrow, I will have 1 JB to steady it and then see how it goes from there.
How frequently do you scan Libre? The more often you scan, the better your understanding you get of how it works and how your body works. I scan about 30 times a day which you may consider excessive and I certainly don't do anything with much of that information but it gives me a really good insight into what is going on and how my body is responding and reassurance that my diabetes is behaving or a tip off that things are going haywire. If I can keep my levels in range (3.9-10) as much as possible my diabetes is much easier to manage. I proactively correct before I hit 10 to maintain that as much as possible, because that makes it easier and my Libre is more reliable at that level.

I appreciate that if you are unwell and suffering with infections then it will be tougher but I would encourage you to perhaps scan more often to get more familiar with your Libre and particularly after a correction to keep a close eye on how your levels are responding to prevent such nasty hypos happening again. No reason why you need to wait until you are hypo before you take action. The huge advantage of the alarms on Libre are that you can head them off before they get below 4.

By the way, what are JBs??