CGM Log (how long do they last, why do they fail)

[SimonP]

I thought it might be interesting/useful to log some information about how long my libre2s are lasting, and why they are failing. I assume it's not just me, but without more data it's quite hard to know. It might also be useful for those who self-fund to have a better understanding of how well the devices work (not just the libre, the more the merrier!)

I've added data available from when I started simply emailing the details to Abbott rather than sitting on the phone, but this does at least record all of the failures since then. Once I have a dig through the XDrip+ database I can add more sensors and durations/failure modes to the list (though no promises quite when I'll get round to this!)

I'll keep adding new sensors to the bottom as I use them.

Start Date	End Date	Working Duration	Failure cause	Serial Number	Status	Device location	Notes
~28/05/2024	04/06/2024	~7 days	Calibration (reading low)	3MH00YMMTFH		RH outer arm "Bingo wing"
04/0602024	18/06/2024	~14 days	None			LH outer arm "Bingo wing"
18/06/2024	21/06/2024	~3 days	Bluetooth failure	3MH00ZZU6P4	RW8NEF5305	RH outer arm "Bingo wing"
21/06/2024	05/07/2024 ??	14 days ??	None			LH outer arm "Bingo wing"	Assumed from gap
05/07/2024 ??	19/07/2024	14 days ??	None			RH outer arm "Bingo wing"	Assumed from gap
19/07/2024	01/08/2024	~13 days	Calibration (reading low)			LH outer arm "Bingo wing"
01/08/2024	08/08/2024	~6 days	Bluetooth failure	3MH012EAWMW	V1W9YM3227	RH outer arm "Bingo wing"
08/08/2024	17/08/2024	~9 days	Calibration (reading low)			LH outer arm "Bingo wing"
17/08/2024	21/08/2024	3 days	Bluetooth failure	3MH013U4E8W	TN42MVV857	RH outer arm "Bingo wing"
21/08/2024	04/09/24	~14 days	None			RH outer arm "Bingo wing"
04/09/2024	18/09/2024	~14 days	None	3MH0114W894		LH outer arm "Bingo wing"
18/09/2024	21/09/2024	~ 2 days	Bluetooth failure	3MH011W5Z04	Q6A7GX78X4	RH outer arm "Bingo wing"
21/09/2024	05/10/24	~14 days	None	3MH011X050H		LH outer arm "Bingo wing"	Ended ~12h early; worked pretty well, especially good cal over the last few days
05/10/2024	19/10/24	~14 days	None	3MH011DTVMW		RH outer arm "Bingo wing"
19/10/24	1/11/24	~14 days	None	3MH0176NGT0		LH outer arm "Bingo wing"	Ran with an offset of ~2 mmol/l for much of its life but correctable using XDrip+
1/11/24	3/11/24	2 days	Bluetooth failure	3MH0187RU04	TFTFX7KN32	RH outer arm "Bingo wing"	Replaced late evening. 2h comms failure on first night, then a 9h ongoing failure from morning of 3rd day. Changing now.
3/11/24	14/11/24	11 days	Calibration error (reading too low)	3MH016W5PVM	(NQW618G1E0)	LH outer arm "Bingo wing"	Developed a 3mmol/l linear offset at ~11 days. Uncorrectable, replaced
14/11/24	28/11/24	14 days	None	3MH017YDLND	AAD7GH12N5	RH outer arm "Bingo wing"
28/11/24	1/12/24	3 days	Bluetooth failure	3MH016H5EY4	9LPMJG3KN4	LH outer arm "Bingo wing"
1/12/24	9/12/24	~8 days (though in reality I should have changed it on day 2 once it showed no signs of improving)	Calibration error (~4.5mmol/l lower than actual finger prick)	3MH01807T2H	LP5RP9NWV4	RH outer arm "Bingo wing"	Massive (~4.5mmol/l offset from days 2 - 5 ; now slightly reduced to 3.5mmol/l which XDrip+ can more easily handle. Very noisy sensor throughout, will be glad to be done with this one.) Just had it replaced as it just reverted to an offset which was too large for XDrip+.
9/12/24	21/12/24	~12 days	Bluetooth failed	3MH019K0L9R	WQ6HLDVPX0	LH outer arm "Bingo wing"	Worked well, some drop-outs, eventually Bluetooth gave up completely
21/12/24	01/01/25	~10 days	Bluetooth failed	3MH01C3Z10M	XALKA77932	RH outer arm "Bingo wing"	Worked well aside from a 2 day period towards the end after a rapid rise + fall (and sensor offline) when the calibration went too far out for XDrip+ (4mmol/l lower than reality) - I stuck with it and had another rapid rise + offline event which put the calibration back somewhere useful. Then Bluetooth failed, despite my not scanning with my phone when I had drop outs (and they happened every couple of days)
01/01/25	15/01/25	~14 days	None	3MH01C2V6A8	DNLMML5R05	LH outer arm "Bingo wing"	Worked ok
15/01/25	24/01/25	~9 days	Bluetooth failed	3MH019JYYER	ZN7CMUUGQ1	RH outer arm "Bingo wing"	Some drop outs, no manual scanning. Eventually died and wouldn't come back (8h of no comms while at work)
24/01/25	7/02/25	13+ days	Bluetooth failed	3MH01807T2M	VA5748FN94	LH outer arm "Bingo wing"	Some dropouts, a few days towards the end with a poor calibration, which then fixed itself. BT died for good early in the morning of the last day (~17h early)
7/02/25	21/02/25	14 days	None	3MH019XQPW0	6G5V0VENN4 -> X21FD1VRQ2	RH outer arm "Bingo wing"	No major issues, calibration was pretty decent throughout, some drop-outs but not for more than 30min. No scanning with my phone aside from startup.
21/02/25	4/3/25	11 days	Bluetooth failure	3MH01CFCM7H	H31F7WJ0C7 -> N8ZLR0XWD6	LH outer arm "Bingo wing"	Worked pretty well until BLE stopped at lunchtime today. There was a 1h drop-out last night too, but I was asleep
4/3/25	4/3/25	0 days	Immediate sensor error (after 1h warm-up)	3MH01DHX63W	69ZLHT3761 -> F66A1JE501	RH outer arm "Bingo wing"	Never returned any data
4/3/25	18/3/25	14 days	No problem	3MH01D1JNYH	7X9UC3T3Z5 -> E1ALCLZWD1	RH outer arm "Bingo wing"	Let's have another go... fingers crossed!
18/3/25	[23/3/25] 1/4/25	[4.5 days] 9.5 days	Bluetooth failed for 8h @ 4.5days, then came back to life until sensor error with 4.5 days to go	3MH018Y8750	KFKCYEUDE7 -> D977J197A6 (not final status, couldn't read sensor with official reader after starting new one)	LH outer arm "Bingo wing"	Comms error for 8h, but recovered, then sensor error so replaced
23/3/25	23/3/25	0 days	Immediate sensor error (after 1h warm-up)	3MH01CFCFDR	KZD545H9E6	RH outer arm "Bingo wing"	Never returned any data
1/4/25	11/4/25	~9 days	comms failure	3MH016Q1KND	QU60EEH433	RH outer arm "Bingo wing"	First Libre2+, comms error
11/4/25	25/4/25	14 days	ok	3MH01977AV0	NP08KNUTV5	LH outer arm "Bingo wing"	, back to a left over libre2
25/4/25	9/5/25	14 days	ok	3MH01FKDDTR	RN7N8QHJA1	RH outer arm "Bingo wing"
9/5/25	6/6/25	15 days	ok	3MH016Q1J9D	KZVWFNZ083 -> Z79YK1V7X1	LH outer arm "Bingo wing"
6/6/25	14/6/25	~7 days	Died with error message (365)	3MH01GQEPF0	DA73UY1GE7 > KGXG70JEN6	RH outer arm "Bingo wing"	Has a 4mmol/l offset (reading too low) towards the top of the normal range, but much closer to fingerprick at the bottom so calibration worked(ish.) Died overnight and told me to replace it
14/6/25	24/6/25	10	Ongoing poor calibration, eventual comms failure	3MH01GQEL2H	DF3H0KCNG4 -> 2UU90DD937	RH outer arm "Bingo wing"	Ran with a consistent 3 - 5mmol/l offset across the range (lower offset at low BG so could still just be calibrated and still detect hypos). Comms failure at the end
24/6/25	29/6/25	5	Bluetooth failure (also had large negative offset, but generally correctable)	3MH01919XD4	W0YGGY1L40 -> MX1G6W21Y5	RH upper tummy - new spot!	1h comms drop-out on first evening, followed by a 6h drop-out overnight. Eventually came back to life (I didn't replace it as needed to get to work). Negative offset throughout though generally just about correctable (~4mmol/l). Final Bluetooth failure (7h+) and replacement.
29/6/25	7/7/25	7 days	Bluetooth failure (>12h)	3MH01G7GJW0	TXXXYJAN71 ->	LH upper tummy	Negative 1.5mmol/l offset - correctable.
7/7/25				3MH01GA517D		RH upper tummy	Current sensor.

Last update: 12/07/2025

 

[rebrascora]

I had one fail recently on day 12.... details below... Otherwise it is well over a year, possibly 2 since my last problem with a Libre sensor.

Failed 18th August on day 12 and just suddenly stopped giving readings during the night. All fine at bedtime but woke at 4.04am hypo and it wouldn't scan and said it had ended using both the reader and the phone app. Still VERY securely attached, so I don't think the filament could have dislodged. I use a reader as my primary device so I rely on NFC to scan to get readings, but it didn't alarm for the hypo either which would be BT so wonder if the battery had failed.
Serial number 3MH010RZGLD and error code 3,365P
It was replaced by Abbott without any problem, even though it only had a day and a half to go.

 

[SB2015]

I am using Medtronic Guardian4 sensors which should last 7 days. As I am using it in a HCL it needs to be reliable and if the system is in any doubt it will ask me to make checks, which is irritating as it is usually at the mos pt inconvenient moments, but not unreasonable as it is doing most of the work of managing my diabetes for me.

I have had 4 out of 39 replaced because of :

• Big bleed (1)
• Fell off on insertion - no glue in tape (1)
• Ended early (2)

These are always replaced for me. You can do this online or by phoning.

I am switching to Simplera sensors at the end of this month.

 

[JJay]

My list would be very boring I’m afraid. 6 failures (I think) in 6 years and none for over a year now. From memory:

3 ended early
2 signal loss which couldn’t be restored
1 never got going in the first place

Also 1or 2 lost on door frames etc but they were down to my own carelessness so I don’t consider it appropriate to ask for replacement.

 

[SimonP]

My list would be very boring I’m afraid. 6 failures (I think) in 6 years and none for over a year now. From memory:

3 ended early
2 signal loss which couldn’t be restored
1 never got going in the first place

Also 1or 2 lost on door frames etc but they were down to my own carelessness so I don’t consider it appropriate to ask for replacement.

Are these currently libre2s and presumably they were previously libre1s? How do you scan them? Mobile phone/Libre2 reader for CGM functionality with the libre2? Thanks.

 

[JJay]

Are these currently libre2s and presumably they were previously libre1s? How do you scan them? Mobile phone/Libre2 reader for CGM functionality with the libre2? Thanks.

Yes, Libre 1s initially, then moved to 2 when available. I’ve only ever used an iPhone to scan/CGM. Found the reader clunky and non-intuitive right from the off, plus I’ve no wish to be carrying extra tech around with me.

 

[PurpleTrout]

I thought it might be interesting/useful to log some information about how long my libre2s are lasting, and why they are failing. I assume it's not just me, but without more data it's quite hard to know. It might also be useful for those who self-fund to have a better understanding of how well the devices work (not just the libre, the more the merrier!)

I've added data available from when I started simply emailing the details to Abbott rather than sitting on the phone, but this does at least record all of the failures since then. Once I have a dig through the XDrip+ database I can add more sensors and durations/failure modes to the list (though no promises quite when I'll get round to this!)

I'll keep adding new sensors to the bottom as I use them.

Start Date	End Date	Working Duration	Failure cause	Serial Number	Status	Device location	Notes
~28/05/2024	04/06/2024	~7 days	Calibration (reading low)	3MH00YMMTFH		RH outer arm "Bingo wing"
04/0602024	18/06/2024	~14 days	None			LH outer arm "Bingo wing"
18/06/2024	21/06/2024	~3 days	Bluetooth failure	3MH00ZZU6P4	RW8NEF5305	RH outer arm "Bingo wing"
21/06/2024	05/07/2024 ??	14 days ??	None			LH outer arm "Bingo wing"	Assumed from gap
05/07/2024 ??	19/07/2024	14 days ??	None			RH outer arm "Bingo wing"	Assumed from gap
19/07/2024	01/08/2024	~13 days	Calibration (reading low)			LH outer arm "Bingo wing"
01/08/2024	08/08/2024	~6 days	Bluetooth failure	3MH012EAWMW	V1W9YM3227	RH outer arm "Bingo wing"
08/08/2024	17/08/2024	~9 days	Calibration (reading low)			LH outer arm "Bingo wing"
17/08/2024	21/08/2024	3 days	Bluetooth failure	3MH013U4E8W	TN42MVV857	RH outer arm "Bingo wing"
21/08/2024	04/09/24	~14 days	None			RH outer arm "Bingo wing"
04/09/2024	18/09/2024	~14 days	None	3MH0114W894		LH outer arm "Bingo wing"
18/09/2024	21/09/2024	~ 2 days	Bluetooth failure	3MH011W5Z04	Q6A7GX78X4	RH outer arm "Bingo wing"
21/09/2024				3MH011X050H		LH outer arm "Bingo wing"	Current sensor

I’ve been using Libre 2 for about 6 months and have had about 4 failures. They always replace but never seem to address the issues that I raise, the worst being that I frequently loose connection when the reading is crashing. This is worrying because it always gives the wait 10 minutes and try again message. Twice it’s come back with sub 3 readings!

 

[helli]

I’ve been using Libre 2 for about 6 months and have had about 4 failures. They always replace but never seem to address the issues that I raise, the worst being that I frequently loose connection when the reading is crashing. This is worrying because it always gives the wait 10 minutes and try again message. Twice it’s come back with sub 3 readings!

But the advice is to always test with a finger prick when BG is low.

 

[SimonP]

I’ve been using Libre 2 for about 6 months and have had about 4 failures. They always replace but never seem to address the issues that I raise, the worst being that I frequently loose connection when the reading is crashing. This is worrying because it always gives the wait 10 minutes and try again message. Twice it’s come back with sub 3 readings!

Fast positive and negative rates of change make mine go offline (and perform a recal as it will sometimes no longer have an offset when it comes back online) - I assume they don't expect this sort of BG trend so assume there may be a failure. In an ideal world this would be the case, but not always in my world....

 

[goodybags]

I’ve only used 4 so far
had 2 replaced by Abbot

First one
was having re-connection issues
although as it was the first one I’ve ever used it might’ve been me not having everything fully switched on on my phone (possibly) anyway when I phoned Abbot for advice more than to report a fault or to moan, they asked me for the error codes, they explained patiently where these were stored in the app,
then said they would send me a replacement FOC.

I then had one fail last week
It was late in the evening, it simply lost connection and wouldn’t re-connect, after an hour of trying to reconnect every 10 minutes it said it needs replacement
I reported it to Abbot (that time via their on-line reporting) they emailed me next day and sent a replacement

 

[PhoebeC]

I think I’ve only had 4-5 errors since March 2020. And apart from the most recent libre 2 plus failures they all happened as soon as I put it on, either bent, didn’t stick or errored straight away.
I’ve knocked a few off but that’s user error not device error.
Odd you’ve had so many. They just don’t like some peoples bodies.

 

[Carlos]

I don't think I've had more than two or three genuine failures, ie sensors loosing connection irrecoverably or finishing too soon since May 2020, when I started using libre. That includes libre 1, 2 and 2+.

I had a few where the filament failed to insert properly in a short period of time, until I worked out that I was not pushing the applicator sufficiently quickly. I would classify those as user errors, rather than sensor error, but Abbott still replaced all of them.

 

[Tdm]

Fast positive and negative rates of change make mine go offline (and perform a recal as it will sometimes no longer have an offset when it comes back online) - I assume they don't expect this sort of BG trend so assume there may be a failure. In an ideal world this would be the case, but not always in my world....

I fohnd this with libre too. I got a dexcom g6, and it just doesn't happen anymore.
I have had a couple of g6s pack up early, but a it more reliable, for me, than libre

 

[SimonP]

I wonder what it is about me - I get two definite failure modes: One is the sensor calibration being massively off, sometimes the calibration wanders around and often resets itself to a different offset (after a rapid +ve/-ve rate of change which causes is to go offline for a period of time), but these are generally ok and stay around the correct value, in other cases the sensor very soon after being applied has a massive offset and it never gets much better. I wonder if this is something to do with where I place the sensor - whether it's not exposed to the right amount of interstitial fluid or gets damaged fairly quickly due to placement - I have very little excess fat on my arms, so what I call the "bingo wing" location seems like the best bet, though even this is pretty close to muscle so I could see it getting damaged in normal use.

The second failure mode is Bluetooth giving up the ghost, this is more weird as other people apparently don't tend to get this. It definitely happens as I can run a BLE scanner app and see other devices in the house, but the libre2 is simply not transmitting any more (i.e. it's not a case of my needing to restart Bluetooth on the phone, etc.). I start the sensor with the Libre 2 reader and thereafter only use Juglucco to read the sensor - this should be a passive thing as the libre2 sensor transmits and the app listens, the only potential interaction is using the phone/juglucco to do an NFC scan of the sensor to link to it, and then subsequently if the sensor goes offline to see what the problem is. Reading about the LimiTTer devices (https://github.com/JoernL/LimiTTer/issues) I see mention of people killing sensors by doing something wrong, though it's not overly clear what the actual cause is - whether it's something to do with the phone NFC chipset (too much power?), wrong commands being used (though one assumes this ought to not kill a device being read, unless it's also writing and to the wrong address.) Perhaps there's something similar going on here, I guess I should simply try to not use the NFC read at all (after the first tap to link) and see if it reduces these failures.

 

[goodybags]

Was thinking maybe I should’ve report the one I’m currently wearing as yesterday evening it was reading over 15 ok I know I was high because of what I ate but a BGM test showed as 11
although today looks more normal

 

[helli]

Was thinking maybe I should’ve report the one I’m currently wearing as yesterday evening it was reading over 15 ok I know I was high because of what I ate but a BGM test showed as 11
although today looks more normal

CGMs are designed to be most accurate at ,"normal" BG (between about 4 and 9). Outside of this range, they should be double checked with a finger prick as they have a ten6to over egg highs and lows.
The other thing to remember is the 15% accuracy standard for both finger prick and CGM. If your "true" BG was 13, your finger prick could read as low as 11 and your CGM could read as high as 15 whilst both comply with the standard.

I would not report a sensor as inaccurate based on one high reading.

 

[Lucyr]

Was thinking maybe I should’ve report the one I’m currently wearing as yesterday evening it was reading over 15 ok I know I was high because of what I ate but a BGM test showed as 11
although today looks more normal

You would need 3 pairs of readings proving it’s inaccurate to report it

 

[SimonP]

And all spaced apart in time (e.g. across a whole day or longer ideally unless the offset is really extreme) and across a range of BG readings and all with the arrow flat.

 

[goodybags]

Thanks for your advice

 

[Merluza]

I’ve been using Libre2s for about 6 months so that’s something like 12-14 sensors. I’ve had 4 failures, these have always ended up just stopping working. This feels like it’s getting close to an unacceptable level of failure at around 25%. Of the remainder 2 or 3 have been accurate with the rest being ok or only just worth using. They have always been replaced when they failed.

When they are accurate they are fantastic but I’m beginning to question whether they are worth the faff when they are 2 points below and I have to learn to ignore them. I recently had 5 days without one due to a failure and I had no replacement and went back to finger pricking and I didn’t really feel the loss and maybe even felt a sense of freedom.

I’m travelling at the moment so I am finding it more useful and thankfully the sensor I’m using is accurate. I’m an amateur musician and often find myself playing or in workshops and the sensor is at its most useful for me then. Otherwise not so much.

Are you able to draw any conclusions from your records @SimonP?