Libre vs bm

Hi Bunnie60
I have the same problem.

Diagnosed Type2 15th August 2021 HbA1c 72. December 2021 HbA1c down to 40 diet mostly, I couldn’t tolerate Metforman.

Checking BM 5 times per day with Safe AQ glucose meter. Decided to try Freestyle Libre.

I am getting a variation in the readings between finger prick & Libre.

Libre can be between 0.5 & 1.6 above the finger prick.

Which one should I trust & why is there a variation?

The blood test meter is deemed to be more accurate, so should be trusted over the libre.

scot russell said:

Which one should I trust & why is there a variation?

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There is a variation cos the libre (and other CGM's) use interstitial fluid to work out your sugar level rather than your blood and whilst it can get very similar results it is not always - there is extra some info here: https://freestylediabetes.co.uk/freestyle-libre/flash-glucose-monitoring-temp

For me the libre always seemed to show about 1ish mmol/L below my blood glucose meter

Rokaab said:

The blood test meter is deemed to be more accurate, so should be trusted over the libre.


There is a variation cos the libre (and other CGM's) use interstitial fluid to work out your sugar level rather than your blood and whilst it can get very similar results it is not always - there is extra some info here: https://freestylediabetes.co.uk/freestyle-libre/flash-glucose-monitoring-temp

For me the libre always seemed to show about 1ish mmol/L below my blood glucose meter

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Great thanks.

I was also worried about this when I had the Libre 2 on trial. My dietitian said the difference of a whole 1 out wasn't to worry about. She said two BM's could show difference of this. But also the Libre is measuring fluid not blood. I also think the Libre readings are what your BM will show in 30 minutes or so. That's my understanding of it. But I'm new to all this

Ipodlistener said:

I also think the Libre readings are what your BM will show in 30 minutes or so.

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There are loads of threads about Libre (the Search function on the top right of the page will help you find them).

The lag has been mentioned multiple times and the way it is handled is different for Libre 2 compared to the earlier version.
As you say, CGMs and Flash GMs such as Libre read interstitial fluid which is different to blood. There is a lag between these readings ... it 's only 10 to 20 minutes. However, the algorithm Libre 2 uses to convert the ISR to BG takes the delay into consideration by extrapolating the graph.

I highly recommend reading through some of the Libre threads to understand its limitations, It is a fantastic tool but only if you understand what it cannot and does not do. Blindly using it to replace finger pricks will leave you disappointed and wasting money.

In Response said:

the algorithm Libre 2 uses

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That algoritm is so genius it knows in advance when you will be climbing a hill or get up or whatever and decreases the delay to only 2 minutes . In my case even less, if I get up within 2 minutes my BG is raised by at least one point, because somehow the algoritme knows I just got up and it works every time.