2 out of 2 Freestyle Libre 2 devices I tried are inaccurate - are CGMs just not for me?

[mouninha]

Hi everyone,

I have gestational diabetes and decided to try to Freestyle Libre 2 CGM at my own cost to reduce the amount of blood testing I have to do and learn more about how my body responds to what I eat.

But so far it's been incredibly confusing: I followed all the instructions on how to apply the sensor to the T (when removing the first one I also confirmed the filament was not bent or anything), but:
- at best - which was the case with my 1st sensor - Freestyle had a >1.1 and up to 2+mmol/L difference with my blood glucose test for ~48h, then it started getting closer to my blood glucose test but frequently the error would still be around 0.7-0.8
- at worst - which is what I'm getting with my second sensor they sent me as a replacement - I'm now at day 4 with the sensor on, and it's still giving me bogus readings eg: telling me I'm constantly at 3-3.9 since last night when I have no hypo symptoms and testing my blood glucose to compare shows it's actually 3.1mmol/L higher than Freestyle is saying

I've contacted Abbott about this and researched extensively online, so I heard all the usual possible explanations (wrong placement, compression error, ...) which I don't think are happening here.

So I'm now wondering: are there people for whom CGMs or at least Freestyle's Libre 2 just doesn't work?

Do they find that alternatives (Libre 3, Dexcom G7) work or it's hopeless to subject yourself to the emotional roller coaster of trying to figure this out?

Would love any personal experiences you've had that could help

thanks a mil

P.S: my diabetic midwife team is providing ZERO help and they're not planning to. Their advice was "follow the manufacturer troubleshooting guides and just stick to one blood testing device because otherwise it's confusing"...

 

[Bruce Stephens]

So I'm now wondering: are there people for whom CGMs or at least Freestyle's Libre 2 just doesn't work?

Yes, certainly some people find Libre 2 doesn't work for them.

Do they find that alternatives (Libre 3, Dexcom G7) work

I think most find that another one works but I think I've heard of some who say they've not found one that does.

 

[Inka]

Welcome @mouninha 🙂 It sounds like your first Libre sensor was good. I found they varied a lot and in the end they just seemed pretty inaccurate. I now use the Dexcom G7, which is fantastic. I hardly ever fingerprick now.

I think you need to decide which option to go with:

- use the Libre in conjunction with fingerpricks and report any inaccurate sensors
- swap to Dexcom (there’s a cheaper Dexcom called Dexcom One)
- stick to fingerpricks

In case you’re dismissing the 3rd option above, I’ve had 3 pregnancies with Type 1 diabetes and I fingerpricked only for all of them (no Libre, etc available then). I did up to 14 fingerpricks a day but they were targeted and allowed me to keep my HbA1C in the 30s. Simple but accurate.

 

[rebrascora]

Hi and welcome

It sounds like your first sensor was pretty good, but you might benefit from applying a new sensor a day or two before you actually start it. This means that the tissue that the filament is embedded in has a chance to respond to this foreign object in it's midst and settle down before it starts sampling the interstitial fluid. I know Abbott don't specifically recommend this but it is a practice that many of us have found helpful.

Libre tends to read about 1mmol lower than my Caresens BG meter, but I have no way of knowing which is nearer the truth. The BG meter is generally considered more reliable but that doesn't necessarily mean to say it is more accurate, and I am fine with Libre up to 2mmols different as long as it is reasonably consistently so ie. always lower or always higher. More than 2mmols out, then it should be reported to Abbott who will usually want 3 comparison tests showing a significant difference in order to replace it.

Part of the problem can be when levels are changing direction, either going up and then coming down or vice versa. This is because the Libre system uses an algorithm to try to make up for the time lag between interstitial fluid and blood. The way this works is to take it's previous readings and extrapolate them to predict 10-15 mins into the future to give an idea of blood glucose actually is. If your levels are rising sharply towards a peak and then coming down the Libre will usually continue to predict them rising until it sees progressively decreasing levels. It then plots the graph and you may see some readings you have taken hanging above or below the line of the graph although now with full CGM you probably only get that if you actually scan or log a reading with a note attached. So you might have a reading of 9.3 with a vertical upwards arrow like I did yesterday but I had insulin on board an I did a bit of exercise and my levels came straight back down and the graph shows that I actually didn't go above 8, so the algorithm overpredicted that 9.3 and then corrected when it realised that my blood levels were coming down.

Generally I compare Libre with a finger prick when my levels are mid range 4-7 and have been stable for at least half an hour with no carbs or insulin active. That way I get a reasonable comparison. Above 10 and Libre is more likely to be further out and as I said, it usually reads about 1mmol lower than BG for me generally so if I am 4.8 it might show me as 3.8. If it is within 1-2 mmol I am still very happy to calculate my insulin doses and correction from it and apart from a couple of tests on each sensor in the first couple of days I rarely need more finger pricks for that fortnight. The more you use it, the more you get used to it's idiosyncrasies and adjust your thinking and diabetes management.

Your second sensor sounds like it might have a kinked filament. This can sometimes happen if the sensor gets caught on something like a sports bra strap and lifted a bit on one side and then pushed back down. Gradually you become better at not catching it on stuff but in the early days it is quite common. Abbott should replace that second one if you report it.

I appreciate that you are self funding these, so this info is probably too late for you, but for anyone else reading this, there is a free 14 day trial of Libre ie. one sensor if you have diabetes and a suitable phone. In your scenario, getting that trial sensor and then a replacement if it under performed would have meant that you did not yet need to fork anything out of your own pocket at this stage, although I am not sure that Abbott would have replaced the first one as it seems to have been fine from what you have said, but perhaps your expectation was a bit high. I do think there may be an issue with the second one though.

Really sorry to hear that you are not getting much support from midwife team. I think that is quite unusual and I hope that improves for you. As others have said, if Libre doesn't suit you, then sometimes one of the other systems will work better, but adjusting your expectation may be necessary.

Wishing you all the very best with your pregnancy and a smooth and successful delivery.

 

[mouninha]

Thank you all so much for your replies so far, they're incredibly helpful

@Bruce Stephens @Inka it's very reassuring to hear that there's a possibility that Freestyle Libre 2 doesn't suit me but that Dexcom might work better (I just got one to try, fingers crossed!)

@rebrascora thanks so much for that concise explanation of the mechanisms generating the Freestyle readings, I've observed the exact changes in scanned readings vs. final graph (or what I see in the csv I download from Libreview) and I suspected something like what you're describing is behind those but I couldn't easily find those explanations on the Abbott documentation so I didn't trust my guess.

And ack that probably my expectation of accuracy was too high as it sounds like after all my first sensor wasn't so bad. That's a good reality check to have and the tip of installing it 48h in advance is so good and makes sense, I'll try that for the next.

I've had an unpleasant skin reaction when removing the first sensor so I think I need a few more days before I can work up the courage to remove the 2nd one which sounds like indeed it's just faulty because it's still 1.6-3mmol/L different than my blood glucose, so it's not even a consistent error I can just "offset"

 

[rebrascora]

If you are having an allergic reaction to the adhesive then there are options like skin tac spray to spray on your skin before you apply the Libre which essentially forms a barrier.... assuming you aren't allergic to the spray, or use an under patch and and apply the Libre over/through that. Hopefully someone else can suggest options for under patches.
You can also get straps and over patches to give the sensor a bit more protection. I have an arm strap that I got off ebay which is essentially a 3D printed plastic watch face which fits exactly around the circumference of the sensor and an adjustable elastic strap to keep it in place. They come in a range of colours from flesh tones to loud and proud neons and pastels to match outfits etc. I have had mine 2 years now and it has saved my sensors many times when the strap has got pinged but the sensor has remained firmly attached. I think it also gives the sensor support during the initial few hours when the adhesive is bonding with the skin. Plus it acts as a visual reminder to me as to which arm the sensor is on when I get in the shower for a good scrub and towel drying afterwards, as a hot shower or bath can warm the adhesive and make it a little less robust.

They really are a great bit of kit once you get used to them and learn how to get the best from them, but I think most of us had a few teething problems at first and there are definitely some people whose body chemistry just doesn't work with the algorithm it uses. Those people seem to find Dexcom works better but when you are self funding, it can be a more expensive system.

Anyway, I am pleased you managed to follow my rambling post above about how the mechanism works and why it can lead to disparity between BG and Libre readings at certain times and that that has reassured you a bit about the readings you are getting or at least were getting from the first sensor anyway. Many people have a similar issue with finger prick BG readings initially when they start double checking readings a few seconds after the first and find they can sometimes be more than 1mmol difference, from different fingers or even the same drop of blood. Having Libre on one arm and comparing to a finger prick on the other hand can also lead to disparity because our blood is not homogenous. The readings given to a decimal place lead us to believe they are accurate to that level when they actually aren't, so sometimes you just have to accept that near enough is near enough.

 

[Proud to be erratic]

Hello @mouninha, Welcome to the forum. Sorry to hear that your introduction to Libre 2 has been pretty difficult.

I persisted with Libre 2 even though I endured over 50% failures; I had no choice, it was all that was available to me at that time. Then the revised NICE Guidelines allowed me a degree of choice. I moved onto Dexcom One, still on prescription which was a lot more accurate and a bit more reliable, but still not great. I then self-funded Dexcom G7, 10 days per sensor rather than the 14 for Libre 2, initially I bought 1, then 3 at a slightly cheaper rate and then started on a qtly subscription, ie 9 at a time and a bit cheaper again. G7 has been very good. Very luckily for me a plea for help at my 6 monthly Endo consult was accepted and now I get G7 on prescription from the Hospital (rather than my GP). [I suspect

G7 has proved amazingly reliable as a sensor; the phone app has had some "moments" of angst but I have also got a Reader from my Hospital prescription which always works regardless of Internet, phone compatibility etc. Also the Reader works alongside and independent of my phone.

I suggest a possible way ahead for you would be to persist with at least 4 sensors (ie a nominal 2 months) and thus have better certainty that Libre 2 is not working for you. Then if your GP is prescribing CGM for you ask to switch to Dexcom One. This would be a no extra cost than a Libre 2 prescription, but be aware that Dexcom One is a 2 part sysyem with sensors that last 10 days and a transmitter that last 90 days and is transferred from one sensor to the next (9 times).

If your GP doesn't prescribe CGM for you and you are still self-funding then you have the option of trying the lower cost Dexcom One or the more expensive G7. G7 is not dissimilar to Libre 2 in that is a one piece device, ie a combined sensor and transmitter - but only lasts 10 days vs 14 days for L2.

Thank you all so much for your replies so far, they're incredibly helpful

@Bruce Stephens @Inka it's very reassuring to hear that there's a possibility that Freestyle Libre 2 doesn't suit me but that Dexcom might work better (I just got one to try, fingers crossed!)

@rebrascora thanks so much for that concise explanation of the mechanisms generating the Freestyle readings, I've observed the exact changes in scanned readings vs. final graph (or what I see in the csv I download from Libreview) and I suspected something like what you're describing is behind those but I couldn't easily find those explanations on the Abbott documentation so I didn't trust my guess.

And ack that probably my expectation of accuracy was too high as it sounds like after all my first sensor wasn't so bad. That's a good reality check to have and the tip of installing it 48h in advance is so good and makes sense, I'll try that for the next.

Spot on.

I've had an unpleasant skin reaction when removing the first sensor so I think I need a few more days before I can work up the courage to remove the 2nd one which sounds like indeed it's just faulty because it's still 1.6-3mmol/L different than my blood glucose, so it's not even a consistent error I can just "ooffset"

But do persist, I managed to make headway with all my useless sensors and Abbott did replace every failure. CGM is soooo much better than finger pricking if you can work with it. Even when it's not brilliant.

 

[Philip Eckersley]

Hi everyone,

I have gestational diabetes and decided to try to Freestyle Libre 2 CGM at my own cost to reduce the amount of blood testing I have to do and learn more about how my body responds to what I eat.

But so far it's been incredibly confusing: I followed all the instructions on how to apply the sensor to the T (when removing the first one I also confirmed the filament was not bent or anything), but:
- at best - which was the case with my 1st sensor - Freestyle had a >1.1 and up to 2+mmol/L difference with my blood glucose test for ~48h, then it started getting closer to my blood glucose test but frequently the error would still be around 0.7-0.8
- at worst - which is what I'm getting with my second sensor they sent me as a replacement - I'm now at day 4 with the sensor on, and it's still giving me bogus readings eg: telling me I'm constantly at 3-3.9 since last night when I have no hypo symptoms and testing my blood glucose to compare shows it's actually 3.1mmol/L higher than Freestyle is saying

I've contacted Abbott about this and researched extensively online, so I heard all the usual possible explanations (wrong placement, compression error, ...) which I don't think are happening here.

So I'm now wondering: are there people for whom CGMs or at least Freestyle's Libre 2 just doesn't work?

Do they find that alternatives (Libre 3, Dexcom G7) work or it's hopeless to subject yourself to the emotional roller coaster of trying to figure this out?

Would love any personal experiences you've had that could help

thanks a mil

P.S: my diabetic midwife team is providing ZERO help and they're not planning to. Their advice was "follow the manufacturer troubleshooting guides and just stick to one blood testing device because otherwise it's confusing"...

I'm glad you said that because I tried it out after using Dexcom G6 for 8 years and gave up after 2 months and went back. I found that the readings were often way off mark compared to blood tests after 10 minutes. Usually 2 or 3 points higher which is useless for a clinical decision. I'm type 1 so calculating insulin doses on faulty data could have serious repercussions for me. Hope this helps.

 

[Vivi M]

Hi and welcome

It sounds like your first sensor was pretty good, but you might benefit from applying a new sensor a day or two before you actually start it. This means that the tissue that the filament is embedded in has a chance to respond to this foreign object in it's midst and settle down before it starts sampling the interstitial fluid. I know Abbott don't specifically recommend this but it is a practice that many of us have found helpful.

Libre tends to read about 1mmol lower than my Caresens BG meter, but I have no way of knowing which is nearer the truth. The BG meter is generally considered more reliable but that doesn't necessarily mean to say it is more accurate, and I am fine with Libre up to 2mmols different as long as it is reasonably consistently so ie. always lower or always higher. More than 2mmols out, then it should be reported to Abbott who will usually want 3 comparison tests showing a significant difference in order to replace it.

Part of the problem can be when levels are changing direction, either going up and then coming down or vice versa. This is because the Libre system uses an algorithm to try to make up for the time lag between interstitial fluid and blood. The way this works is to take it's previous readings and extrapolate them to predict 10-15 mins into the future to give an idea of blood glucose actually is. If your levels are rising sharply towards a peak and then coming down the Libre will usually continue to predict them rising until it sees progressively decreasing levels. It then plots the graph and you may see some readings you have taken hanging above or below the line of the graph although now with full CGM you probably only get that if you actually scan or log a reading with a note attached. So you might have a reading of 9.3 with a vertical upwards arrow like I did yesterday but I had insulin on board an I did a bit of exercise and my levels came straight back down and the graph shows that I actually didn't go above 8, so the algorithm overpredicted that 9.3 and then corrected when it realised that my blood levels were coming down.

Generally I compare Libre with a finger prick when my levels are mid range 4-7 and have been stable for at least half an hour with no carbs or insulin active. That way I get a reasonable comparison. Above 10 and Libre is more likely to be further out and as I said, it usually reads about 1mmol lower than BG for me generally so if I am 4.8 it might show me as 3.8. If it is within 1-2 mmol I am still very happy to calculate my insulin doses and correction from it and apart from a couple of tests on each sensor in the first couple of days I rarely need more finger pricks for that fortnight. The more you use it, the more you get used to it's idiosyncrasies and adjust your thinking and diabetes management.

Your second sensor sounds like it might have a kinked filament. This can sometimes happen if the sensor gets caught on something like a sports bra strap and lifted a bit on one side and then pushed back down. Gradually you become better at not catching it on stuff but in the early days it is quite common. Abbott should replace that second one if you report it.

I appreciate that you are self funding these, so this info is probably too late for you, but for anyone else reading this, there is a free 14 day trial of Libre ie. one sensor if you have diabetes and a suitable phone. In your scenario, getting that trial sensor and then a replacement if it under performed would have meant that you did not yet need to fork anything out of your own pocket at this stage, although I am not sure that Abbott would have replaced the first one as it seems to have been fine from what you have said, but perhaps your expectation was a bit high. I do think there may be an issue with the second one though.

Really sorry to hear that you are not getting much support from midwife team. I think that is quite unusual and I hope that improves for you. As others have said, if Libre doesn't suit you, then sometimes one of the other systems will work better, but adjusting your expectation may be necessary.

Wishing you all the very best with your pregnancy and a smooth and successful delivery.

This is one of the best explanations on Libre I have read - Abbott should employ you to write their user manual!

 

[rebrascora]

This is one of the best explanations on Libre I have read - Abbott should employ you to write their user manual!

Thanks. I wasn't sure if I had made it clear enough. It is quite difficult to convey just in words.

 

[mouninha]

quick update: I removed my faulty Freestyle Libre 2 (surprisingly the filament looked just fine) and just got my Dexcom G7 today.

Unfortunately the Dexcom is also showing me in a constant hypo since it finished warmup ~3h ago, started at 3.9 ant continuously dropped until now where it's even stopped showing a number and just indicates LOW.

Fingers crossed that it will come to its senses overnight, because I did think the applicator and the app both look better quality than Freestyle, I'll keep this thread updated!

 

[Lucyr]

quick update: I removed my faulty Freestyle Libre 2 (surprisingly the filament looked just fine) and just got my Dexcom G7 today.

Unfortunately the Dexcom is also showing me in a constant hypo since it finished warmup ~3h ago, started at 3.9 ant continuously dropped until now where it's even stopped showing a number and just indicates LOW.

Fingers crossed that it will come to its senses overnight, because I did think the applicator and the app both look better quality than Freestyle, I'll keep this thread updated!

Good luck. Do you drink enough? With any cgm type keeping well hydrated is recommended, so just wondered if that could be an issue for you?

 

[mouninha]

thank you for the tip! I'm drinking loads yes, 3L a day or more!

I keep wondering if I did something wrong at application:
- did I place it wrong? because it's not exaaaactly the back of my arm it ended up slightly away from my body (and the previous erroneous Freestyle was a bit towards the body)
- did I not press hard enough for the 10seconds they asked to do so (I'm so uncomfortable with needles so I hard a hard time with that)
- do I have a bit too much fat at the back of my arm and the sensor doesn't like that?
but it seems unlikely...

Instead I see some things suggesting that some people's bodies have reactions to the introduction of a foreign object that alters the glucose availability around the injection site (like this piece https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3737647/), that increasingly seems like the more likely explanation for me. Maybe I got away with the first sensor, then my body built up this reaction?

We shall see, I'll keep you posted

 

[mouninha]

Documenting my first 48h+ with the Dexcom G7:
- First 24h continued the nonsense I mentioned 2 posts ago: oscillating around 3.9, then crashing so low it stopped showing numbers at all and just indicated LOW (and many times sensor errors where it stopped displaying readings for ~30min at a time)
- Next 24h: it seemed to gradually get closer to my BG readings, with errors starting at 1.7-1.9 mmol/L then gradually reducing to 0.5-0.2, but later I caught 2 more errors at 1.5.

By that point, I called their technical support hoping to get more guidance than I did with Freestyle (Freestyle's responses were invariably "oh this happens let us send you a replacement sensor" - even by the 2nd sensor I had trouble with, they had no interest in avoiding sending me a third by trying to figure out if something deeper was going on. I guess it's good at least that they replace them no questions asked). Turns out they were more helpful: they told me about the calibration feature and said if I still have readings not matching my BG after 3 calibrations, to call them so they can send a replacement.

So that's what I've been doing and this morning Dexcom was within 0.1 mmol/L of my BG, but I guess I'll see how it develops over the course of today and report back!

 

[Tdm]

I find most dexcoms accurate 'out of the box' but occasionally they do take 24 hrs to bed in.
It does seem to take longer in this case for the sensor to get over 'insertion trauma'...it may be a one off or it may be your body chemistry.
On any sensor you will get occasional times where its out if levels are changing rapidly.
I wouldn't count differences of 0.5 as an error...as your blood testing strips aren't 100% accurate either.
Keep at it...your next dexcom may ded in quicker

 

[mouninha]

thank you @Tdm !

Re BG reference: fair point yes! I've also subjected myself to repeat BG tests to check that and indeed, I caught different BG readings (pricking different fingers / sides of the same finger) within ~1min of each other showing very different numbers.
eg1: 7.0, 7.5, 8.3, 7.4, 7.1.
eg2: 8.3, 7.7, 7.7.

Re Dexcom: yes Dexcom technical support mentioned exactly that insertion trauma (it makes sense to me somehow because my experience with piercings is that my body is generally unhappy with those foreign objects, even surgical grade titanium ones, it just never heals around them. Dunno if that makes sense). Will keep at it! I'm hopeful that the calibration is going to help in my case as I'm seeing the readings get closer. I think I have the patience for this sensor + one more attempt (by then I'll have tried 5 sensors: 3 freestyle, 2 Dexcom), if it still doesn't work after that I might declare myself defeated because the stress has been real given I only have 1.5 months left in my pregnancy so not a ton of time to figure things out 🙂 I'd try again after the birth if my diabetes is still there then