Demo Libra is not 15 minutes behind

[Vamppir8]

They say Libra is 15 minutes behind as it's in skin fluid so somebody explain how diabox shows it live? 2 hours post breakfast, insulin worn off, rising 0.2. inject 2 units, 1 minute later down at 0.2. it can only be the Libras apps algorithm slowing it up.

 

[Robin]

I don’t think the injection and the reduction in the amount of glucose in your interstitial fluid can really be linked. It’s unlikely that insulin would have had an effect that quickly. The amount of glucose passing through the capillaries and interstitial fluid must vary all the time, your blood system is not homogenous, and this probbaly accounts for the tiny change in the reading.

 

[helli]

NOOOOOOOO!

Libre 2 is NOT 15 minutes behind.
Interstitial fluid readings are 15 minutes behind finger pricks but Libre accounts for this delay.

Whilst Libre reads interstitial fluid, it applies an algorithm to convert this to blood glucose readings. As part of this calculation, it takes into consideration the delay. It does this by extrapolating the current trend and "predicting" the current level.

It is useful to understand how this is done because you may observe some "oddities" if the direction of the trend changes in the last 15 minutes. If this happens, you may see higher or lower values which then "disappear" as the "real" data overwrites the prediction. This becomes most obvious for those of us who may experience hypos. When we treat a hypo the downward trend in levels should quickly change to an upward trend.

I do not know how Diabox accounts for this delay as it uses its own algorithm (I believe Abbott are protective of theirs). However, as @Robin explained, this does not account for your observation. You can only tell the delay when comparing CGM results with fingerpricks.

 

[Vamppir8]

I'm not saying reading is correct lol it was the usual 2.5 out as it always is on way down or up. But the actual injection shows everytime minute or two later turns on a sixpence. How could Libra even know to send signal.

 

[Proud to be erratic]

They say Libra is 15 minutes behind as it's in skin fluid so somebody explain how diabox shows it live? 2 hours post breakfast, insulin worn off, rising 0.2. inject 2 units, 1 minute later down at 0.2. it can only be the Libras apps algorithm slowing it up.

Several thoughts:
As @helli says the 15 mins is the differential between actual and interstitial. Presumably that is also a generic number, since not only are we all different, but that generic difference must be affected by our degree of insulin resistance at any one moment in time.

However the Libre 2 algorithm attempts to predict where it is, in relation to actual, thus provide a shortened time gap - this is claimed to be as little as 2 1/2 mins, but it feels nearer to 5 or 7 mins for me - with or without Diabox. [Realistically I don't think any tighter estimation of that lag is possible by me from flash scans and LibreLink alone]. Then you have a Diabox algorithm taking the Libre 2 output and making its own predictions! I didn't find any detail about Diabox translation of the interstitial to actual relationship (and I got bored and slightly lost following links when doing that research). So I just accept the principle that there is some lag.

While your BG is changing, then any difference between actual and interstitial is essentially much more complex anyway. Comparisons can only be of value when in steady state, ie horizontal trend or 0.0 mmol/L/min change.

Even when at steady state one set of comparison readings is fairly irrelevant. There is still the "randomness of Diabetes" which can make any one reading or any few hours of readings inexplicable! I have found it takes time and lots of "trial and learning" to get comfortable with interpreting the trend visible from Libre 2 on Diabox.

The Diabox app shows just how much interstitial change is going on minute by minute. And if in the Diabox settings you are updating minute by minute, then after a while the app algorithm struggles to just keep up and the individual readings become less reliable; but the Diabox graph does smooth these apparent blips out into the 5 minute plots.

I still have to remind myself to not "overreact" to an isolated reading - yet still to definitely react to a high downward trend. I have my lower downward alert (in settings / more alerts) set for changes at or greater than 0.3mmol/L/min with both vibration and sound. I just monitor only if the downward trend is at 0.2 or less and then make a judgement if that drop continues every 5 minutes. But I'm retired and can "make the time" to do this; also it's much more difficult to respond or even diligently monitor when I'm driving since I am potentially playing with my phone and thus at risk of being prosecuted ... this is one of those conundrums where it makes sense to head off a hypo while driving but with my tech I'm in the zone of "driving without due care and attention!!"

 

[Vamppir8]

Several thoughts:
As @helli says the 15 mins is the differential between actual and interstitial. Presumably that is also a generic number, since not only are we all different, but that generic difference must be affected by our degree of insulin resistance at any one moment in time.

However the Libre 2 algorithm attempts to predict where it is, in relation to actual, thus provide a shortened time gap - this is claimed to be as little as 2 1/2 mins, but it feels nearer to 5 or 7 mins for me - with or without Diabox. [Realistically I don't think any tighter estimation of that lag is possible by me from flash scans and LibreLink alone]. Then you have a Diabox algorithm taking the Libre 2 output and making its own predictions! I didn't find any detail about Diabox translation of the interstitial to actual relationship (and I got bored and slightly lost following links when doing that research). So I just accept the principle that there is some lag.

While your BG is changing, then any difference between actual and interstitial is essentially much more complex anyway. Comparisons can only be of value when in steady state, ie horizontal trend or 0.0 mmol/L/min change.

Even when at steady state one set of comparison readings is fairly irrelevant. There is still the "randomness of Diabetes" which can make any one reading or any few hours of readings inexplicable! I have found it takes time and lots of "trial and learning" to get comfortable with interpreting the trend visible from Libre 2 on Diabox.

The Diabox app shows just how much interstitial change is going on minute by minute. And if in the Diabox settings you are updating minute by minute, then after a while the app algorithm struggles to just keep up and the individual readings become less reliable; but the Diabox graph does smooth these apparent blips out into the 5 minute plots.

I still have to remind myself to not "overreact" to an isolated reading - yet still to definitely react to a high downward trend. I have my lower downward alert (in settings / more alerts) set for changes at or greater than 0.3mmol/L/min with both vibration and sound. I just monitor only if the downward trend is at 0.2 or less and then make a judgement if that drop continues every 5 minutes. But I'm retired and can "make the time" to do this; also it's much more difficult to respond or even diligently monitor when I'm driving since I am potentially playing with my phone and thus at risk of being prosecuted ... this is one of those conundrums where it makes sense to head off a hypo while driving but with my tech I'm in the zone of "driving without due care and attention!!"

Diabox don't use algorithm unless you select it (only for trend arrow). I've spent day comparing with reader, at most they were only .3 difference between the two. Only thing reader algorithm seems to do is just smooth the graph out. I've been having hell of week, turns out faulty sensor it's 4 over blood monitor continuously. Stuck another one on other arm, after a day its 2 out as well. Like you say its only really useful to know if your going up and down, what you are could be 2 to 4 out. Even says on instructions check with blood monitor. But my drs won't let me have them as got libra. I pointed out I am legally bound to use them before I drive so need 4 to 6 just for that.

 

[trophywench]

Hells Bells !!! Libre readings are quite frequently unreliable at figures either way outside the chosen band of 3.9 to 10. It's so far adrift of my actual BG readings there is no way I could ever trust it enough to base my insulin doses on it, so the only thing I really can rely on it for, is trends, and short term seeing if either a correction dose or hypo treatment is working the right way yet. Occasionally I get a sensor that is pretty accurate but this is the exception. If I had to chose one or t'other it would have to be Libre that goes, since only the meter talks to my insulin pump.

 

[Proud to be erratic]

Diabox don't use algorithm unless you select it (only for trend arrow).

I'm very sure that Diabox do use their own algorithm to translate the signal coming from the sensor into a reading on a phone screen. I am confident that Abbott would not share their commercial and confidential algorithm with anyone else, since, apart from the commercial angle, they don't want to attract any legal liability for anybody else "misusing" somehow their sensors and that data. I understand and accept that risk assessment from Abbott's perspective.

I've spent day comparing with reader, at most they were only .3 difference between the two.

I'm moderately happy with both pure and applied maths and did quite a lot within both my degree and subsequently when I got tangled up in error theories for Engineering Surveyors - where cumulative errors could cause havoc. But I think, with only a moderate confidence in this thinking, that to deduce any real trends or differences from the Diabox output, without iAlgorithms or with one of the 2 iAlgorithms offered, needs a substantial set of results over many days. Also it needs the user to be in a fairly steady state as well, not behaving irregularly from the very many factors that can affect diabetes - which can seriously skew results ant the interpretation of those results.

Only thing reader algorithm seems to do is just smooth the graph out.

The iAlgorithms that you refer to are extras offered by Diabox in their settings, for further smoothing of results.

I've been having hell of week, turns out faulty sensor it's 4 over blood monitor continuously.

Sadly, this does just "happen" and frustrating as it can be I've accepted this is so and "roll with it" or muddle through - until the sensor just becomes unworkable.

Stuck another one on other arm, after a day its 2 out as well. Like you say its only really useful to know if your going up and down, what you are could be 2 to 4 out. Even says on instructions check with blood monitor. But my drs won't let me have them as got libra. I pointed out I am legally bound to use them before I drive so need 4 to 6 just for that.

I did originally have a problem with my GP trying to constrain my use of test strips. I emailed with my rationale for why I should not be Rationed ... which worked for a while. There is an expectation (false expectation as far as I'm concerned) that once someone has Libre prescribed their test strip usage should reduce - a lot. That is not the case for me. I've made sure that my Endocrinologist is aware of my high failure rate with Libre and thus I need to still fp a fair bit. He has recorded this in his reports and I used that record when I needed extra test strips; I'd literally run out.

I would suggest an email to your GP spelling out that: Libre is not always reliable (fact) and even when it is Abbott themselves tell you to meter test when out of range; that driving has its own challenges, needing regular confirmation that you are in range; and once hypos and hypers are factored in you could still need, in a week of difficult D management, to meter test many times daily. Failure to provide this vital medication for your diabetes is not only in contradiction of the NICE Guidelines for managing T1, but could have serious consequences.

 

[Proud to be erratic]

Hells Bells !!! Libre readings are quite frequently unreliable at figures either way outside the chosen band of 3.9 to 10. It's so far adrift of my actual BG readings there is no way I could ever trust it enough to base my insulin doses on it, so the only thing I really can rely on it for, is trends, and short term seeing if either a correction dose or hypo treatment is working the right way yet. Occasionally I get a sensor that is pretty accurate but this is the exception. If I had to chose one or t'other it would have to be Libre that goes, since only the meter talks to my insulin pump.

Thank you - interesting comment and useful to know I'm not alone in not overly trusting Libre for insulin dosing.

By meter I presume you mean your finger prick meter or is there something else? If this is from a finger prick, may I ask roughly how many times a day do you need to test? I can imagine that you have been T1 for sufficiently long for your GP Surgery to know to not try and meddle with your prescription needs.

 

[trophywench]

You would think that they wouldn't do things for the sake of it, but these days, no GP can be reasonably expected to know their patients since they have so very many - but we also have to appreciate all the ruddy waste of their time boxes they have to tick in order to keep their surgery open, ie to continue getting NHS funding in order to keep treating 'us lot' - the public. It is indeed a complete PITA usually - but I'd be very happy if they told me there was a better medication to treat anything I happen to need medication for and wanted to discuss it. Plus the fact they do check your BP and other stuff - even though the diabetes clinic at the hospital checks mine and even though they don't/can't prescribe meds for that, if they knew damn well I'd be better off trying Y or Z instead of the X I'm using I'd still expect them to tell my GP that. However, these days it's ME that would have to chase my GP up when nothing heard from them thereafter.

 

[Proud to be erratic]

You would think that they wouldn't do things for the sake of it, but these days, no GP can be reasonably expected to know their patients since they have so very many - but we also have to appreciate all the ruddy waste of their time boxes they have to tick in order to keep their surgery open, ie to continue getting NHS funding in order to keep treating 'us lot' - the public. It is indeed a complete PITA usually - but I'd be very happy if they told me there was a better medication to treat anything I happen to need medication for and wanted to discuss it. Plus the fact they do check your BP and other stuff - even though the diabetes clinic at the hospital checks mine and even though they don't/can't prescribe meds for that, if they knew damn well I'd be better off trying Y or Z instead of the X I'm using I'd still expect them to tell my GP that. However, these days it's ME that would have to chase my GP up when nothing heard from them thereafter.

Even though I am pretty unhappy with the attitude and responsiveness from my GP Surgery since Covid - I do recognise that the Surgery has any number of constraints and contradictions constantly going on. This does mitigate my perspective of their poor performance. I have no doubt about your box-ticking remark.

But I do find there are also times when common sense has completely gone, times when we the public should be sheltered from whatever bureaucracy is creating problems for the Surgery and they should just "suck it up" and not burden us, plus times when my nominated GP needs to use that clever brain and wide general medical knowledge to think a bit more. We are hoping to move to a different County (but by chance within the same ICS) so I've lost motivation to politely yet robustly push back at some of the nonsense. I remain polite, but no longer so prepared to give my time for providing constructive comment; I feel a bit bad about this .... but. I'm putting some time into finding out how the ICS actually works ( or should work!).

Anyway, this has become a big digression from the Post about Libre lag.

 

[Vamppir8]

I'm very sure that Diabox do use their own algorithm to translate the signal coming from the sensor into a reading on a phone screen. I am confident that Abbott would not share their commercial and confidential algorithm with anyone else, since, apart from the commercial angle, they don't want to attract any legal liability for anybody else "misusing" somehow their sensors and that data. I understand and accept that risk assessment from Abbott's perspective.

I'm moderately happy with both pure and applied maths and did quite a lot within both my degree and subsequently when I got tangled up in error theories for Engineering Surveyors - where cumulative errors could cause havoc. But I think, with only a moderate confidence in this thinking, that to deduce any real trends or differences from the Diabox output, without iAlgorithms or with one of the 2 iAlgorithms offered, needs a substantial set of results over many days. Also it needs the user to be in a fairly steady state as well, not behaving irregularly from the very many factors that can affect diabetes - which can seriously skew results ant the interpretation of those results.

The iAlgorithms that you refer to are extras offered by Diabox in their settings, for further smoothing of results.

Sadly, this does just "happen" and frustrating as it can be I've accepted this is so and "roll with it" or muddle through - until the sensor just becomes unworkable.

I did originally have a problem with my GP trying to constrain my use of test strips. I emailed with my rationale for why I should not be Rationed ... which worked for a while. There is an expectation (false expectation as far as I'm concerned) that once someone has Libre prescribed their test strip usage should reduce - a lot. That is not the case for me. I've made sure that my Endocrinologist is aware of my high failure rate with Libre and thus I need to still fp a fair bit. He has recorded this in his reports and I used that record when I needed extra test strips; I'd literally run out.

I would suggest an email to your GP spelling out that: Libre is not always reliable (fact) and even when it is Abbott themselves tell you to meter test when out of range; that driving has its own challenges, needing regular confirmation that you are in range; and once hypos and hypers are factored in you could still need, in a week of difficult D management, to meter test many times daily. Failure to provide this vital medication for your diabetes is not only in contradiction of the NICE Guidelines for managing T1, but could have serious consequences.

Thanks for that, had to ask for test strips 3rd time! Got quite personal this time as begging is not working, at the end of my tether. They deleted my request for insulin, took 2 days, 4 visits, was down to last 10mm on a Friday... had vial left when put in request. Now trying to contact hospital see if they can put pressure on.

 

[Proud to be erratic]

Thanks for that, had to ask for test strips 3rd time! Got quite personal this time as begging is not working, at the end of my tether. They deleted my request for insulin, took 2 days, 4 visits, was down to last 10mm on a Friday... had vial left when put in request. Now trying to contact hospital see if they can put pressure on.

I truly wish you the best of luck in pursuing this through your Hospital team. I'm retired, so can choose where I waste my precious time. But if I had your current challenge and felt I'd explored options with my GP Surgery, I might well turn up at Reception and insist on speaking (most politely, but robustly) with the Practice Manager in person, to explain why and how the Surgery is playing Russian Roulette with their routine prescribing process and my life.

Another route that might help is to seek an Urgent referral to the Surgery's Pharmacy Team. My surgery does not have its own Pharmacy, but does have a Pharmacist - or more accurately has the services of a Pharmacist Consultancy. Thinking about this, I realised that such a service is essential for any GP Surgery and in my case our local Surgery shares a sub-contract with a Consultancy that covers a number of GP Practices locally. In my case this outsourced agency is doing the periodic prescription reviews and when they phoned me recently (about the Dexcom One fiasco) they introduced themselves as my Surgery's Pharmacist. Knowing that office didn't exist within the Surgery building, I probed and found out they were really sub-contractors for my Surgery. I was able to have a sensible discussion with the person who in effect is approving the medicines that the GP is prescribing - approving in the sense that the written prescription complies with what is approved by our ICS and know precisely what the Formulary does and doesn't allow. In my case they have now liaised with the ICS Clinical Pharmacy Team to sort out a nonsense with the Formulary detail - as a result of my prodding the sub-contractor and politely telling them I shouldn't have to be dragged into their internal nonsensical processes.

Again, good luck. Polite but robust dialogue does often succeed.