Freestyle Libre - huge reading errors

[cairntoul]

From what I can see they only recommend/instruct finger pricks if your blood glucose is changing rapidly - as indicated by the arrow when making the measure - due to the lag in interstitial vs. blood glucose measure. The actual slow moving data is represented by abbott as being accurate. If it is not then the use of the thing is becomes very limited - finger tests needed over the first 1-2 days to check accuracy then a test needed before adjusting any dose - shades of the glucowatch and certainly not what abbott portray it as.

For those people using it, do you have confidence in the numbers to an accuracy of 1-2 mmol?

Cheers

 

[DeusXM]

O2 charge me for ringing the number and I am on a business contract. I am going to ring them immediately and question why they insist on charging me and not you?

As I said, I believe it's free but worth double checking. You might actually find that private contracts offer calls to 00800 numbers free, but biz contracts don't. I don't know, I'm not on O2, I'm just going on what I could see on Google and other discussion forums, which is why I said check.

The other options are of course to try the 0800 number I posted or (and here's a wild and dangerous idea) use a landline.

 

[DeusXM]

For those people using it, do you have confidence in the numbers to an accuracy of 1-2 mmol?

Absolutely. Generally the accuracy is within 0.5 mmol/l for me. As I said, I don't actually even bother with fingerstick testing anymore unless the Libre reading does not match up with my expectations.

 

[Diabeticliberty]

As I said, I believe it's free but worth double checking. You might actually find that private contracts offer calls to 00800 numbers free, but biz contracts don't. I don't know, I'm not on O2, I'm just going on what I could see on Google and other discussion forums, which is why I said check.

The other options are of course to try the 0800 number I posted or (and here's a wild and dangerous idea) use a landline.

I do like to live on the edge sometimes but using landlines is just a bit too much like naked parachuting. You can end up with someone else's equipment in your mouth. If you do wild and dangerous yourself I don't suppose you've tried this have you? 😉

 

[Robin]

I'm with Deus XM here, once I've done a few spot checks over the first few days of the sensor, if they accord with my meter, (and they usually do in the mid range) I don't bother to finger prick unless I'm driving ( you still have to finger prick by law every two hours). I find my Libre usually reads lower than my meter at the bottom end, and higher at top end ( over 10, say) but only by about 10% or so. I've just been using a sensor ( I use one for holidays, and sometimes in between times just to keep a closer eye on things) and I did have one reading that was surprisingly different, but I scanned again ten minutes later, and it was spot on with what my meter had said. You get used to the time lag.
I found mine invaluable for sorting out my nighttime readings. No 3am alarms needed, and I got far more useful data from just a few nights than I'd have got with months of waking up and spot checking with a meter.

 

[Northerner]

For me, I wouldn't be that interested in the numbers - I'm pretty comfortable with my awareness and general control. I probably wouldn't use it full time either as my diabetes and predictable lifestyle wouldn't warrant it, but I would be interested in seeing rise and fall, and extent, which might inform my insulin dosage timings. Whatever you think about them, and even if they are only reliable for 50% of people, they are a step forward and we've come a long way from boiling up your urine in a pan and sending it off to a lab to find out if you can have a second Rich Tea with your cocoa 🙂 I wouldn't adjust insulin dosage on the basis of any readings because I don't need to (due to 'weird' diabetes! 😉)

 

[Radders]

My initial idea was to get the starter pack, which is a reader and two sensors, to help in testing my basal rates and get some insight into how to adjust my pump during exercise. However subject to the same issues as described above in the first 16-24 hours of a new sensor, and the time lag, I have found it on the whole to be pretty accurate. I made a spreadsheet comparing finger prick and Libre readings and the average difference was less than 1. I now do a finger prick before correcting or if the Libre reading is out of target range and before going out on my bike. This has reduced the number of finger pricks drastically and given me some very useful insights into the mealtime spikes, the timing of boluses, and how protein affects my levels, to name but three. I am hooked.

 

[cairntoul]

Well after 26 hours the latest is Libre 9, Finger 5. The scale factor is 0.6 (multiply Libre reading by 0.6 to get the finger reading). This increases to 0.75 as the libre reading drops towards 4 (gets more accurate).

So if it doesnt get better after another day then it'll be back on the phone.

Even if it does improve it is a big concern that this is not clearly publicised by Abbott in terms of accuracy/safety, never mind that the sensor is sold as a 14 day part and may need a 1/2/3 burn in - 3 days is 20% of its advertised lifetime(!)

 

[AndBreathe]

Well after 26 hours the latest is Libre 9, Finger 5. The scale factor is 0.6 (multiply Libre reading by 0.6 to get the finger reading). This increases to 0.75 as the libre reading drops towards 4 (gets more accurate).

So if it doesnt get better after another day then it'll be back on the phone.

Even if it does improve it is a big concern that this is not clearly publicised by Abbott in terms of accuracy/safety, never mind that the sensor is sold as a 14 day part and may need a 1/2/3 burn in - 3 days is 20% of its advertised lifetime(!)

Not everyone uses or needs to apply then wait, or apply then accept some wonky levels. As I said earlier, I think some people's immunse system is just a bit frisky. I'd count myself in there. Once you've used a small number of sensors you will likely find it easier to ignore the sensor for a while before getting scan-tastic.

 

[Robin]

If you are one of the people for whom it needs 24 hours to settle ( and I am) then inserting the sensor but not activating it for 24 hrs means you still get the full 14 days out of it.

 

[everydayupsanddowns]

Folks, thanks for the input.

I was aware, anecdotally, of people having a 24hour bed in time. However this it's not mentioned anywhere in the manual (from what I can see), and there's a big difference in an error of 1,2 or even 3 mmol/L and one of 8. Even after 15 hours the error was huge (libre 9, finger 5). Then after 21 hours Libre 14, finger 8.

I did phone. The advisor did say that this could happen, but acknowledged that it was not explicit anywhere.

It's really odd... I've seen presentatinos where Abbott have recorded different MARD (mean absolute relative difference) for the first 24 hours and felt sure it was mentioned in the manual, but like you I cannot find it.

I am another who has always had really useful information from Libre sensors over the past 2 or 3 years. I only use them occasionally for a bit of a 'reset', but I find that my BGs and range always significantly improve during the course of the 2 weeks from all the extra information.

For me it boils down to taking decisions based on information, rather than guesswork - and being able to see what is going on 20-30 times a day rather than 6-8. But as has been suggested, this only really applies if you are getting a decent data-feed from the device. Like DeusXM I am far more used to differences of around 0.5mmol/L with only a few times in the day when it would be 1-2mmol/L out. Perhaps it has to do with biochemistry?

In your shoes I would certainly be contacting Abbott for a replacement as the sensor you are currently wearing seems to be performing outside of expected tolerances. It may settle in time (I had one that took 5 days before coming into line) but as you say... that is hardly ideal for a £50 sensor with a 14 day limit!

Would be interested to see what happens if you try another one - did you get the starter pack with 2 sensors in it?

 

[cairntoul]

Hi folks, just short of 2 days and still out by a scale factor of roughly 0.6, so a massive error. This indicates that it is not sensor burn in. It also indicates a need to verify sensor performance with finger tests, which is a bit self defeating. I'll give it another day before contacting them which will allow me to gather more data.

I see that the glimp app seems to allow some form of calibration so may try that before ditching this sensor - nothing to lose now.

 

[DeusXM]

Hi folks, just short of 2 days and still out by a scale factor of roughly 0.6, so a massive error. This indicates that it is not sensor burn in. It also indicates a need to verify sensor performance with finger tests, which is a bit self defeating. I'll give it another day before contacting them which will allow me to gather more data.

I see that the glimp app seems to allow some form of calibration so may try that before ditching this sensor - nothing to lose now.

My maths isn't great - by scale factor, do you mean your readings are out by 0.6mmol/l, or something different? If it's 0.6 mmol/l, that's perfectly acceptable - you'd likely get this variance by using a different finger on one blood sugar meter.

Also, I know it's a nitpicking point, but Abbott have never said the Libre replaces finger tests, it's simply a way of more effectively gauging trends. There is a school of thought that runs it doesn't matter if the Libre is inaccurate as long as it is consistently inaccurate ie. as long as the margin of error is the same.

I really wouldn't bother giving it another day. Abbott tend to be very good at replacing duff sensors, so rather than spend another 24 hours getting frustrated at something that is obviously broken, I would just call Abbott from a landline, get a new one sent out and chalk this one up to bad luck. If you keep it in for too long, all you're going to do is give Abbott the arguement "well, you stuck with it for this long so evidently it wasn't that much of a problem." You're also, as I said, just making yourself frustrated, which won't have a positive impact on your blood sugar.

I would also add that Glimp is not your friend in this, I found that it could read anything from exactly what was on the 'official' reader to 10mmol/l higher. Glimp is a third-party app and not endorsed by Abbott and so any readings taken with it should be interpreted as dubious at best. If you're using your phone as a reader, stop and use the proper reader first.

 

[cairntoul]

Hi there, the scale factor is what I need to multiply the libre reading by in order to get the finger reading.

So libre reading 10 = finger reading 6.

The scale reduces as the libre reading increases. It becomes more inaccurate.

Libre reading 16 = finger reading 8.

The 0.6 scale is the average.

 

[sacol4940]

I'm trialling a sensor at the moment.. Sometime the Libre readings match the finger prick test, and sometimes they're way out... I only bolus based on the fingers prick test so I'm not too concerned. I'm just using the Libre to look for trends etc...

 

[Thomas Hill]

Sorry to dig up this old thread but google searching seems to bring this to the foreground mainly because Abbot Support staff are quoting people's experiences rather than their own documentation.

I'm on the 8th sensor and it's consistently reading 3-5mmol below my blood sugar after 14-hours.
So 2.2 after the first hour but my finger is reading: 6.5
6 hours later a reading of 3.8 was reporting: 8.7.
I appreciate there is a 15-minute delay, but previous readers have been 0.5-1mmol out previously.

Contacting Abbot support their first operative could not find my account, which is odd because they've sent me a replacement before.
The second operative I spoke to said that the device takes 24-hours to 'get used to the body'.

I actually think the '24 hours to settle down' myth has occurred because of forums and posts like this one.
In Europe the Libre has a 1-hour 'warm-up' period.
Once it's completed the device must be ready to use.
Otherwise it would need a '24 hour warn-up period'.
In the US, the period is '12-hours' and the device cannot be used in this window.

No where in the manual nor user-guide does it say it will be inaccurate for the first 24 hours.

In fact the Operating Manual provides the clinical trial results which says the opposite.
Stating the following: Page 47 - "Agreement on Day 1 against YSI Reference"
At 8-12hours 0.8% of readings were outside the +/-40% YSI comparison

Page 58 reports the Mean Absolute Relative Difference of Day 1 to be 13.8% - Changing to 13.3% on Days 2-5.
Page 59 reports the Mean Absolute Relative Difference for Blood Glucose readings for Day 1 15%.

So the device shouldn't be any more than 15% out and the results show there is a a small percentage difference between the first day and later days.
My current device roughly -60% out!

Interestingly the documentation also says: 167 sensors produced glucose readings and are included in the analysis. There were 35 sensors that failed at insertion. I wonder what classes a 'failure' in their study.

I'd also like people to consider how your body will acclimatize to the libre site.
If the bruising is affecting reading - it will take 3-4 days the the tissue to recover, in which case the device is inaccurate for much longer than 24-hours. But this isn't documented.
If your body is reacting to the sterile filament like a splinter, it will get worse over 24-hours, not better. Have you left a splinter in for more than 24hours? Your body doesn't forget about it after 24hours, it will continue to fight against the foreign body. But again that's not documented.

I believe the Abbot support staff are simply telling people to call again in 24-hours and accept the inaccuracy, even though Abbot's clinical trials document the acceptable ranges.

Anyway.... I'm going to call support again. But don't want others to accept faulty devices!