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Freestyle Libre Calibration

H

HeartBreakHigh

Member
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6
Hi. Yes ANOTHER freestyle libre post. I was going to post in one of the others, but don´t think this has been specifically addressed yet.

So, re the calibration of the freestyle libre reader (and or other ways of monitoring the sensors). I have read on here that people say there is a 20 minute time lag, BUT on the Freestyle libre website itself they claim there is an approximate lag of 5 minutes and on another related post they claim a 2.4 minute time lag for adults:

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Interstitial fluid readings and blood glucose readings don’t always match

Glucose in the blood takes time to make its way into the interstitial fluid so there may be a lag time. The average lag time between the FreeStyle Libre 2 sensor and blood glucose readings is by about 2.1 minutes for children and about 2.4 minutes for adult

https://freestylediabetes.co.uk/freestyle-libre/flash-glucose-monitoring-temp
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And they quote some study (that´s also published on Pubmed amongst others)

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  • 8 Alva S, et al. Accuracy of a 14-Day Factory-Calibrated Continuous Glucose Monitoring System With Advanced Algorithm in Pediatric and Adult Population With Diabetes. Journal of Diabetes Science and Technology. September 2020. doi:10.1177/1932296820958754
https://pubmed.ncbi.nlm.nih.gov/32954812/
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The average lag time of the FreeStyle Libre system is approximately 5 minutes. 3 This is why ISF glucose and blood glucose measurements taken at the same time won't always match - and in fact - are likely to be different. 1. Rebrin K, Steil GM. Can interstitial glucose assessment replace blood glucose measurements?
https://www.freestyle.abbott/ca/en/products/libre/faqs.html
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So ultimately. What´s the evidence and science behind the "20 minute" lag time and where did it come from? Which claim is correct? Can anyone post the reviewed evidence?

I´m sure we can all agree that there is a massive difference between the 2.4 minutes (2.1 for children) or 5 minutes as posted on the websites and the 20 minutes that is often quoted on here.

Have I missed something?


EDIT: Added the links as original posting flagged them as spam.
 
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I think the 15/20 minute time lag refers to Libre 1. What you have posted refers to Libre 2.
 
Hi @HeartBreakHigh

I'm finding the L2 more accurate than it's predecessor.

The "20 minute lag" is with the BG meter.? There has always been one. (Well, twix 15/20.ish.)
Some folk panIc because they have tested & treated the hypo then tested a few minutes later & say they dropped further.. It's a "snapshot in time" 20 minutes back.


I Would concur the Libre is reasonably on the ball. I use Xdrip the graph is a linear series of dots registering every 5 minutes. So, I test count 4 dots back on the Xdrip graph. By tapping on a dot shows that point in time stamp & the BG.
If it comes within 0.6mmol to the meter? I'm happy.

What I have found with both versions of the sensor is comming up off a low is slower than the meter says, which is slightly slower to how I feel..

But yeah, I've been questioned here if I got that right. Either test then wait 20 & scan or count back on the Xdrip graph to 20 minutes ago & compare to what the meter just the threw up on the screen..
 

I'm sure that anyone could Google this and find a number of science papers with different numbers. The answer is not simple.



Source

After having crossed swords with an Abbott person before regarding a claim they were making about accuracy of the L1 I am not surprised to see that they are claiming that their device is better than the conventionally accepted science. For marketing purposes, they will of course use the most advantageous data.
 
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You will have these statements many times on this forum but it is always worthwhile reminding ourselves
- CGMs (and Libre) do not measure blood sugars. They measure interstitial fluids which is a different thing.
- We are all different. Some of us may have a 5 minute delay of finger pricks behind CGMs, some of us have 20 minute delays

The other things to remember are
- the delay is not constant. If our blood sugars are changing quickly, the difference may be more
- CGM manufacturers use an algorithm to convert interstitial fluid readings to blood sugar readings. They include some prediction within this algorithm to minimise the delay. They (believe they) are getting better with their predictions so may suggest they are not as far behind.

And, when I think is the most important thing
- much of what we measure and count with diabetes is an approximation. Finger prick readings and CGM readings are as approximate as carb counting. So, getting worrying about 15 minute, 20 minute, 5 minute or any other delay isn't worthwhile in the overall scale of approximations as long as we realise there is likely to be a delay and to back up CGM readings with finger pricks if we are going to make corrections. (Actually, the OP doesn't say whether they are taking insulin so I don't know if this is relevant)
 
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