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Libre 2
- Thread starter Homer
- Start date
Leadinglights
Well-Known Member
- Relationship to Diabetes
- Type 2
I may depend on how high or low your levels are as to how close each will be. When high it can be way out.
How high are is your BG @Homer?
Accuracy is measured as a percentage - all meters, both CGM and finger prick, should be within 15% accuracy. But bear in mind, your finger prick meter could be reporting on the low side so the difference could be up to 30%.
For example, if your "real" BG is 10mmol/l, the finger prick could be reporting as low as 8.5 and your Libre could be reporting as high as 11.5. And CGMs are designed to be most accurate at "normal" levels. When your BG is in double figures, CGM readings can be erratic - highs are often over exaggerated.
The other thing to consider is "insertion trauma" - our bodies react to having an alien object inserted into our arm. This can also cause erratic readings (at al levels) until it settles down after a day or so. It is common to insert Libre a day before activating for this reason.
Another thing to consider is how much fat you have where you have inserted the sensor. The filament requires at least 5mm fat. Without this, the readings can be unreliable. For me, the readings were low but I guess they may also be too high.
Finally, there are faulty sensors. If you find your sensor fails or reports consistently too high or low when your BG is at "normal levels" and was inserted more than a couple of days ago, you must report it to Abbott (you can do so via their website or phone). They usually replace them but may ask for the old one back so do not throw it out.
Accuracy is measured as a percentage - all meters, both CGM and finger prick, should be within 15% accuracy. But bear in mind, your finger prick meter could be reporting on the low side so the difference could be up to 30%.
For example, if your "real" BG is 10mmol/l, the finger prick could be reporting as low as 8.5 and your Libre could be reporting as high as 11.5. And CGMs are designed to be most accurate at "normal" levels. When your BG is in double figures, CGM readings can be erratic - highs are often over exaggerated.
The other thing to consider is "insertion trauma" - our bodies react to having an alien object inserted into our arm. This can also cause erratic readings (at al levels) until it settles down after a day or so. It is common to insert Libre a day before activating for this reason.
Another thing to consider is how much fat you have where you have inserted the sensor. The filament requires at least 5mm fat. Without this, the readings can be unreliable. For me, the readings were low but I guess they may also be too high.
Finally, there are faulty sensors. If you find your sensor fails or reports consistently too high or low when your BG is at "normal levels" and was inserted more than a couple of days ago, you must report it to Abbott (you can do so via their website or phone). They usually replace them but may ask for the old one back so do not throw it out.
rebrascora
Well-Known Member
- Relationship to Diabetes
- Type 1
- Pronouns
- She/Her
Just to add to all the excellent points made so far, dehydration will also impact Libre more than blood. The body tries to maintain the water content of blood more consistently than interstitial fluid, so if you are dehydrated at all the body will raid fluid from the interstitial fluid to keep your blood right. Dehydration means that the concentration of glucose in your interstitial fluid will increase, so that again can cause disparity between Libre and finger prick.
Unless I am hypo or very hyper I tend to only double check my Libre with a finger prick when my levels are mid range and stable ie. Libre has my readings as being in the 5-7 range with an horizontal arrow for at least half an hour with no obvious carbs or insulin active. If Libre is within 2mmols in that situation I am happy to trust it for all normal diabetes decisions.
At high (above 10) or low (below 4) I usually defer to a finger prick for making whatever diabetic decisions I need to make.
Libre is usually within 1mmol of my finger prick result when in range (4-10) and I rarely check it more than twice in the 14 day period (usually in the first couple of days of use) unless I am hypo or hyper. At those times I don't worry too much if it is out by more than 2 because it is my finger prick which guides me in those situations..... the Libre high or low just prompts me to finger prick.
Also important to know that if you lie on your sensor in your sleep it can cause what we call a "compression low" where the tissue under the sensor that the filament is sampling becomes compressed and causes it to register a false low, so particularly important not to panic about the low alarm going off during the night. Think about your sleeping position when the alarm wakes you up. Were you lying on the sensor arm and does your graph show a sudden dip into the red which is usually caused by a compression whereas your basal insulin will usually cause a slow steady decline. Obviously, if you feel hypo then treat straight away but if you don't feel hypo, double check with a finger prick and always check recovery from a hypo 15 mins after treatment with a finger prick. Libre will almost always show your levels continuing to drop 15 mins after a hypo treatment whereas a finger prick will show your levels recovering. If you rely on Libre for this, you will over treat almost every hypo and end up going too high
Unless I am hypo or very hyper I tend to only double check my Libre with a finger prick when my levels are mid range and stable ie. Libre has my readings as being in the 5-7 range with an horizontal arrow for at least half an hour with no obvious carbs or insulin active. If Libre is within 2mmols in that situation I am happy to trust it for all normal diabetes decisions.
At high (above 10) or low (below 4) I usually defer to a finger prick for making whatever diabetic decisions I need to make.
Libre is usually within 1mmol of my finger prick result when in range (4-10) and I rarely check it more than twice in the 14 day period (usually in the first couple of days of use) unless I am hypo or hyper. At those times I don't worry too much if it is out by more than 2 because it is my finger prick which guides me in those situations..... the Libre high or low just prompts me to finger prick.
Also important to know that if you lie on your sensor in your sleep it can cause what we call a "compression low" where the tissue under the sensor that the filament is sampling becomes compressed and causes it to register a false low, so particularly important not to panic about the low alarm going off during the night. Think about your sleeping position when the alarm wakes you up. Were you lying on the sensor arm and does your graph show a sudden dip into the red which is usually caused by a compression whereas your basal insulin will usually cause a slow steady decline. Obviously, if you feel hypo then treat straight away but if you don't feel hypo, double check with a finger prick and always check recovery from a hypo 15 mins after treatment with a finger prick. Libre will almost always show your levels continuing to drop 15 mins after a hypo treatment whereas a finger prick will show your levels recovering. If you rely on Libre for this, you will over treat almost every hypo and end up going too high
Thanks for that, it puts my mind at rest, never had it like that before.
Will take everything you have said
Cheers Barbara
Very good information, I’m glad I posted, thanks for the help
My HBA1c (blood test) is 65, my Libre 2 indicated 51 mmol, currently my estimated A1c Libre 2 reading has risen to 57mmol and i'm not sure why so i contacted my DN today for some advice as i'm awaiting surgery, the DN has given me an appointment for 30/09/24 i take Levimere (72) and Novorapid (8) along with Metformin & Gliclazide, i am concerned that with a rising HBA1c i will not be able to have the surgery that i have waited 5 years for.