Discrepancy between LibreLink scanner and pin prick test.

[mmorgan]

Wonder if anyone else has experienced this: mum's alarm is being activated 6-7 times per day, generally from about 4 pm onwards. It can alarm for low blood sugar within an hour of eating dinner. For example, this afternoon the alarm went off and it was 3.7. When i did the pin prick blood test it was 8.1. It is generally 3-5 above what the libra scanner says. This has only happened for the last 3 weeks. We have changed the arm disc 3 times. And it is still the same. I feel I should be going on the pin prick test result as I find it alarming there is a massive different between the two. Any advice gratefully received. Thanks.

 

[Pam123]

I have had this problem with the last to Libre but the other way round its reading between 2 and 4 higher, i had the first one replaced by Abbott this one i s one week old now and isn't quite as bad as the other one was.

You should report it to Abbott they will replace it for your mum

 

[Inka]

@mmorgan Make sure you mum is hydrated as dehydration can mess with the result. Also, ensure she’s not inadvertently pressing on the sensor eg by the way she’s sitting or having tight sleeves, etc.

Report any persistently faulty sensors to Abbot so she can get them replaced. Always go by the fingerprick if uncertain.

 

[rebrascora]

Is she leaning or lying on the arm with the sensor on it? Libre are prone to what we call "compression lows" where if you apply pressure to the sensor such that it compresses the tissue under the sensor, then it will cause the reading to drop to false lows. This is most common during the night, where you might roll over in your sleep onto the arm with the sensor, but I can imagine it is also possible with someone who perhaps isn't very mobile and leans on it whilst sitting in a chair.
The other thing to understand is that Libre reads interstitial fluid glucose levels not blood and interstitial fluid is usually about 15mins behind glucose. The algorithm programmed into the Libre system tries to make up for this time lag bu taking the previous readings and extrapolating them forward to predict what the Blood Glucose level will be in 15mins time. This works pretty well when levels are changing quite uniformly either going up or coming down, but if they rise or fall rapidly and then tail off and perhaps change direction, this is when Libre will be a bit wide of the mark. So if your mother's levels were dropping quite fast due to injected insulin and then her digestive system started to release glucose from her food, the Libre will often predict her levels dropping for a further 15-30 mins until it realises that levels are now rising. During that time, Libre will be at it's greatest difference from a finger prick, but you are right that the finger prick is the more reliable and therefore to go with what it shows you when you have cause to double check a Libre result, due to an alarm etc. Generally I do a comparison test or two on each sensor when my levels are steady and mid range (5 or 6mmols) and there is no food or insulin actively affecting my BG levels. This tells me how close to my finger prick reading the sensor is and anything up to 2mmols is workable, generally it is within 1mmol and usually slightly lower, but comparing it when levels are changing fast due to food or insulin will result in more disparity between the finger prick and Libre reading. Gradually you learn to take this issue into consideration when you look at the Libre readings and think about if there are carbs that are likely releasing into the blood stream and bringing levels up but Libre hasn't quite caught on yet or insulin which is taking levels down.

The other thing to be aware of is that dehydration can affect Libre because it is reading interstitial fluid, so if someone is dehydrated, there will be less water in the interstitial fluid and the readings may well be higher and if the person has a good drink, then that can drop those levels back down to where they should actually be. Elderly people have a tendency to suffer with dehydration, so that is important to keep in mind, although that will usually cause Libre to read a bit higher.

 

[everydayupsanddowns]

Sorry to hear your Mum is having trouble with alarms on Libre not being helpful.

There are a whole host of reasons why sensor glucose values may be different from capillary glucose

@helli wrote a handy list of factors to bear in mind here:

CGM limitations and precautions

Moderator Note: This helpful reply was copied from another thread as it details some of the commonly experienced limitations of continuous glucose sensors. My blood sugar has been in perfect range for days now, but although I haven't changed anything, I'm starting to get very short periods of...

forum.diabetes.org.uk

If you are finding the results between fingerpricks and Libre considerably different, the difficulty is you don’t really know which ones are most likely to be showing you results closer to lab values. Fingerstick results are likely to be the ones to trust, but that’s not guaranteed, as fingerstick monitors have an allowable margin of error too. Plus some fingerstick monitors are more likely to gove reliable results than others. It can be a very frustrating business!

It might help to contact Abbott, who will troubleshoot the sensor and are likely to replace any that they think aren’t performing as they would expect.

 

[mmorgan]

Thank you all so much for your help. This is invaluable.

 

[mmorgan]

I have had this problem with the last to Libre but the other way round its reading between 2 and 4 higher, i had the first one replaced by Abbott this one i s one week old now and isn't quite as bad as the other one was.

You should report it to Abbott they will replace it for your mum

I've exchanged a few and Abbotts have been really good. Mum's never had a problem like this before. I had no idea the libre was so sensitive to. Thanks for your input.

 

[mmorgan]

Sorry to hear your Mum is having trouble with alarms on Libre not being helpful.

There are a whole host of reasons why sensor glucose values may be different from capillary glucose

@helli wrote a handy list of factors to bear in mind here:

CGM limitations and precautions

Moderator Note: This helpful reply was copied from another thread as it details some of the commonly experienced limitations of continuous glucose sensors. My blood sugar has been in perfect range for days now, but although I haven't changed anything, I'm starting to get very short periods of...

forum.diabetes.org.uk

If you are finding the results between fingerpricks and Libre considerably different, the difficulty is you don’t really know which ones are most likely to be showing you results closer to lab values. Fingerstick results are likely to be the ones to trust, but that’s not guaranteed, as fingerstick monitors have an allowable margin of error too. Plus some fingerstick monitors are more likely to gove reliable results than others. It can be a very frustrating business!

It might help to contact Abbott, who will troubleshoot the sensor and are likely to replace any that they think aren’t performing as they would expect.

Gosh, it is so complicated. I'm hadn't expected so many problems. To be honest we have had no problems such as these in the last year. The odd one that just didn't work from the get go. But that's it. I'll check out the link. Thanks very much.

 

[mmorgan]

Is she leaning or lying on the arm with the sensor on it? Libre are prone to what we call "compression lows" where if you apply pressure to the sensor such that it compresses the tissue under the sensor, then it will cause the reading to drop to false lows. This is most common during the night, where you might roll over in your sleep onto the arm with the sensor, but I can imagine it is also possible with someone who perhaps isn't very mobile and leans on it whilst sitting in a chair.
The other thing to understand is that Libre reads interstitial fluid glucose levels not blood and interstitial fluid is usually about 15mins behind glucose. The algorithm programmed into the Libre system tries to make up for this time lag bu taking the previous readings and extrapolating them forward to predict what the Blood Glucose level will be in 15mins time. This works pretty well when levels are changing quite uniformly either going up or coming down, but if they rise or fall rapidly and then tail off and perhaps change direction, this is when Libre will be a bit wide of the mark. So if your mother's levels were dropping quite fast due to injected insulin and then her digestive system started to release glucose from her food, the Libre will often predict her levels dropping for a further 15-30 mins until it realises that levels are now rising. During that time, Libre will be at it's greatest difference from a finger prick, but you are right that the finger prick is the more reliable and therefore to go with what it shows you when you have cause to double check a Libre result, due to an alarm etc. Generally I do a comparison test or two on each sensor when my levels are steady and mid range (5 or 6mmols) and there is no food or insulin actively affecting my BG levels. This tells me how close to my finger prick reading the sensor is and anything up to 2mmols is workable, generally it is within 1mmol and usually slightly lower, but comparing it when levels are changing fast due to food or insulin will result in more disparity between the finger prick and Libre reading. Gradually you learn to take this issue into consideration when you look at the Libre readings and think about if there are carbs that are likely releasing into the blood stream and bringing levels up but Libre hasn't quite caught on yet or insulin which is taking levels down.

The other thing to be aware of is that dehydration can affect Libre because it is reading interstitial fluid, so if someone is dehydrated, there will be less water in the interstitial fluid and the readings may well be higher and if the person has a good drink, then that can drop those levels back down to where they should actually be. Elderly people have a tendency to suffer with dehydration, so that is important to keep in mind, although that will usually cause Libre to read a bit higher.

As far as I can tell, the sensor is on the same area it always is. It's so strange. I'm getting in contact with Abbotts today. Thanks for the info.

 

[Magks]

I’ve only using these sensors for 6 weeks and until this morning everything seemed ok. However I woke up to a reading of 3.9 and went down even lower after breakfast of poached eggs on soda bread. so I did the finger prick test and that gave me a reading of 12.3 so now I’m very confused

 

[helli]

@Magks how did you feel?
Did you feel like you were having a hypo?
Did you wash your hands and check again?
It is possible you had something on your fingers which affected the results when you did the finger prick test.
Did you have something applying pressure to your sensor for example were you resting up on it or did you have a strap or clothing which was holding it too tight? It is possible that the sensor was reporting a compression low - a false readding from the sensor because the filament was unable to get access to the interstitial fluid due to the pressure applied.
How long a ago did you apply the latest sensor?
If you applied it in the last 24 hours, you could be experiencing "insertion trauma"- false readings as your body gets used to having an alien object inserted in your arm
Is the sensor well attached?
If the filament moves or becomes kinked after you catch the sensor on something, it will report low readings.
How is the sensor now?
If it is still reading a long way different from checked finger pricks, it is possible that it is a faulty sensor.
You can report this to Abbott through an online form or call them.

 

[Magks]

I felt absolutely fine which is why I did the finger test. It has been wavering between 3.4 and 4 all morning and the sensor ends in 8 days and had some jelly babies just in case but it hasn’t changed anything. My finger prick however reacted to the sweets and now shows 14

 

[Bruce Stephens]

I felt absolutely fine which is why I did the finger test. It has been wavering between 3.4 and 4 all morning and the sensor ends in 8 days and had some jelly babies just in case but it hasn’t changed anything. My finger prick however reacted to the sweets and now shows 14

Sounds like it's developed a fault, and I'd expect Abbott to replace it.

 

[Magks]

Thank you I’m going to give them a ring

 

[helli]

I felt absolutely fine which is why I did the finger test. It has been wavering between 3.4 and 4 all morning and the sensor ends in 8 days and had some jelly babies just in case but it hasn’t changed anything. My finger prick however reacted to the sweets and now shows 14

If there is a significant discrepancy between the sensor and finger pricks, the advice is to always take the finger prick reading. So you did not need the jelly baby (as you later worded out).
However, bear in mind that all meters, both CGM and finger pricks, need to comply with a standard with a 15% accuracy tolerance. So, for example, if your Libre is reporting 12 and your finger prick is reporting 14, this is not a significant discrepancy. Your "true" BG could be 13 and they are both within the standard tolerance.

 

[Magks]

Thank you for the info I will remember this if it happens again. New to all this