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Libre v finger prick

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Smiter55

Well-Known Member
Messages
63
I am currently on a free trial of libre. My readings are way lower than I get with using my contour next. Example just 10 mins ago I scanned at 6 and finger pricked at 12.5. Is this normal? Anyone else trying out the libre and finding that readings are very different.
 
Did you check that 12.5 by repeating the test with a new strip
 
I've also used a Contour Next for most of the time I've been testing. I used the original Libre for a while, and it consistently read 1-1.5 points lower that my meter. BUT, the actual trends and patterns I saw were very similar with both.

If I'd ever seen such a big difference I would have probably suspected a "contaminated" finger, washed hands, and definitely done a re-test with my meter.,
 
Did you give your sensor time to bed in?
It is common to have random readings up to 48 hours after application because our body reacts to the alien object in our arm.
Some bodies are more sensitive to this than others.
I find it is useful to apply my sensor a day or two before starting for this reason.
 
I confess I didn't do that I will try be more patient, unfortunately patience isnt one of my virtues.
 
I did do a retest and got same reading was very odd as someone else suggested it might take time to settle in. I will just keep checking
 
Smiter55 said:
I did do a retest and got same reading was very odd as someone else suggested it might take time to settle in. I will just keep checking
Click to expand...
I'd definitely agree regarding settling in time! For mine, I needed a 48 hour wait before activating , otherwise I'd not get consistently sensible readings for the first couple of days. You can insert a new sensor then not activate it until the old one's expired, so there's no long waiting time involved.
 
I did not realise you could apply the sensor and not activate it. Presumably once activated you would still have your 14 days life left. Could be useful if you know you are going to be travelling when it's time for a new sensor to be applied or in a situation where applying a new sensor would be awkward at that time.
 
It is useful to know that the sensor will always be 5 minutes behind your finger prick test. This is because interstitial fluid, which is what the sensor checks has a time lag of 5 minute from the reading of actual blood. This is why if your level is falling or rising quickly, particularly heading to a downwards low, it's recommended to double check with a finger prick test. Blood levels can sometimes change a lot in 5 minutes. If you want complete and absolute accuracy in the moment, probably best to use finger prick. I've just finished my libre trial and have purchased two more as I'm not eligible for free-funding. I'd be gutted to have to go back to finger pricking I must say. Only check now and again with that.
 
Libre 2 attempts to predict this 5 minute delay. So the value it shows you is what it thinks your current level is (not 5 or 15 minutes ago) based on the current trend.
This is usually pretty good unless your levels are changing direction. For example, when I treat a hypo, Libre will take longe to react to show I have recovered and, typically. "predicts" a lower level than I actually reach.
 
Hi Pip. Not that I am doubting what you are saying. However, I cannot seem to find this info anywhere. Can you tell me where this information comes from. I understand that the the libre shows trends and gives an arrow showing whether it is falling or rising etc. However I have not seen any info on their site that says the reading is not actual and is a prediction. It is a known fact that interstitial readings are approximately 5 minutes behind a blood reading. I know about that fact. Perhaps I've just not spotted that info on the libre site.
 
I assume that question was targeted at me rather than Pip.
Very little of my knowledge has come from the Libre site: it has come from years of experience of using the sensors and chatting with others who have done so.
There are quite a few things which Abbott do not share and comes from "tribal knowledge" from the users which is the great value of a forum such as this.
 
If I may put my 2 cents in.

“Glucose levels can be measured from the bloodstream, or from the interstitial fluid (ISF), the fluid which surrounds the body’s cells, as glucose freely diffuses from capillaries to the interstitial space³. ISF glucose and BG measurements taken simultaneously won’t always match, and, in fact, are likely to be different. There is a 5- to 10-minute delay in ISF glucose response to changes in blood glucose4 which is unlikely to impact routine day-to-day treatment decisions. The average lag time of the FreeStyle Libre system is approximately 5 minutes5 ”

With the newer Libre 2 technology lag-time has been reduced to 2 minutes, which is part of why you can make treatment decisions based on the Libre 2 sensor glucose reading."


Review of Libre / Libre 2 – Waltzing The Dragon Inc.

waltzingthedragon.ca
 
Yes John as I stated in my comment. What I am querying is the post saying that Libre's results include a predicted rise or fall and are not the actual reading. I have rung Libre and they say that this is definitely not the case and if there is too much difference then it may be a faulty sensor. The arrows show trends but are not included as extra readings in the result of the actual scan. According to them.
 




So you can see that from what is said the focus is on the trend that is what the level was what it is and what it may be in the future and so the trend is evaluated and applied to the interstitial reading giving a predictive assessment of what the level is going to be based on the trend it is implicit in what they are saying.
 
I understand all this. So I'm not sure why you keep telling me the same info. I've rung Libre today and asked them the question. Do the trend values get added to the actual readings. They categorically state that no this is not the case. I do understand what a trend is. It's the difference between past and current readings. This denotes which way the arrow is pointing next to the reading. Blood itself is the first thing that registers this change followed by interstitial fluid. Which is what the sensor registers. It has been suggested that Libre use a predicted value based on the trend within the actual reading itself. Libre have said no. That is all I can tell you. I would tend to go with what Libre say as it wouldn't pay them to not fully reveal the truth of how there sensor and app work. Perhaps I'm being naïve.
 
Sorry @onnecar this is not what we mean by "trend". Nothing us "added on".
The line of readings is mathematically extended in the current direction by about 10 minutes and the predicted current reading (the large number at the top of the screen) is thus predicted value. This is not stored. The historical graphs contain the actual reading.
Libre seem to be reluctant to share the knowledge even though it is a common approach for all CGMs.
 
It wasn't me who suggested that anything is (added on). I was actually querying your statement saying that. Either the interstitial reading is current and is the actual reading (nothing to do with the arrows, which are a predicter of trends) or it is not. Libre say the reading is actual although it does lag behind blood as opposed to interstitial. I understand the lag issue. Which is why Libre say to leave 10 minutes between readings to get similar results. I'm only telling you what they've told me.
 
And I am only telling you what I have read and experienced through using CGMs for more than 4 years.
As I said earlier, Abbott does not share some of the idiosyncrasies of the Libre and how valuable it has been to learn from people on the forum who have been through years of experience. There is a kind of tribal knowledge amongst users.

Some people seem to find this difficult to accept. For example, there was a guy once who insisted the battery life of a Libre was exactly 14 days from the point a sensor is applied rather than a software setting that causes the sensor to expire 14 days after activating it. Multiple people on the forum explained how they applied their sensor 2 days before activating to allow it to bed in. But he would not accept this evidence.

Thankfully, we can chose what we want to believe. As I prepare for a 7 hour flight, I believe the early is round but others believe it is flat.
 
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