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Graph Differential: Libre, Phone & Meter

LionChild

Well-Known Member
Messages
325
Location
Birmingham UK
Type of diabetes
Type 1
Treatment type
Insulin
Dislikes
whisky
Has anyone noticed with the Libre (both 1 & 2), that the graph depiction of blood glucose level is always set higher on the libre meter than the phone app? It can make a difference when a hypo is indicated on my phone reading and graph, but does not show on the actual Libre meter. Often this then means that magically, a hypo registers on the phone account of things, when doing the scan, but afterwards, still maintains that I am compliant with 100%.....which is nice, as I feel I get away with it!
What this means I do not know, however. I suppose the sensible thing would be to do a finger prick...which I do, sometimes..
 
I don't know about the difference between the reader and the phone but there have been discussions about a hypo (or a high) appearing when scanning but not on the graphs.
My understanding is that the readings from interstitial fluids are about 15 minutes behind true blood readings. The algorithm that Libre 2 uses to convert interstitial fluid readings to blood sugar readings attempts to predict the value in 15 minutes time. If our levels are trending in a straight line (whether flat, up or down), the prediction is not bad. If the trend changes direction, the prediction will be wrong and the graph will be updated in 15 minutes time so the hypo (or high) will "disappear".

For example, if you have a hypo (which you check with a finger prick because Libre is not as accurate at low levels) and you treat it, the trend will change but Libre will take 15 minutes to notice so may temporarily show your hypo levels lower than they actually go.
 

Thank you IN Response, very helpful as usual!!
 
The sensor takes a reading every 15 mins. You can scan every min during that period but the reading may be an interpolation depending on the previous reading & where it was going at that time. So it looked back at your 150 & saw you were rising say 5mg/dL per min. So 6 mins later you scanned & it gives you 180. The actual reading which it took 9 mins later was in the about 150 so your graph follow this profile. The 180 remains an outlier which you most likely never achieved. That's my understanding anyway.
 
@Ronancastled whilst your comments about interpolation are correct, the sensor does NOT take a reading every 15 minutes. The significance of 15 minutes is that interstitial fluid is 15 minutes behind blood sugar readings.
The sensor takes a reading at least every 5 minutes. I know this for certain because I use an alternative app which takes the readings the sensor makes and updates them every 5 minutes.
 
Keep in mind that there is an error factor with ALL blood glucose measurements (whether blood from the finger or the Libre)
 


I often have this. I've not noticed consistent trends, however quite often the libre app scanning on the phone and the libre handheld reader will give quite different results when scanned no more than seconds apart. I assume it is a difference in the software the app and reader run. But why should the software be different? Has the theory behind converting interstitial fluid to represent blood glucose changed? Confusing.

The difference compared to the test strip reader is more understandable, given the lag (whicg by the way can vary more and much less than 15 minutes) but even the test strips can give quite different readings depending on which finger you use. To make things worse, a couple of journals I've read seem to have the opinion that with increasing technology modern cgms are now as reliable if not more reliable than more traditional blood glucose strip reading metres. So when all 3 methods give different results, which happens at least a few times a month, is it spin the wheel?
 

Ha ha, yes it sometimes seems like it. I have read that any kind of BG test is only a rough guide, even the A1c test is not totally reliable. My partner worked in the hospital lab in biochemistry, and measured these things, and he says there can be a number of reasons why it might be 'out'. So, there you are!
 
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