Is there something wrong with sensor?
Hi, RPa, I've been using libre for about two and a half years now, so about 60 or so sensors in.
Each has a different "personality": some sensors I trust, some are totally dingbat. Use them for a while and it's easier to figure out which are good and which are sketchy.
Fortunately, there's only been about 4 or 5 out of the 60 which have been throwing totally random results like yours (and even those have been ok for a fair bit of the time).
I think you might have just been unlucky in getting a dubious one as your first - they're really not all like that.
Abbott are normally pretty good at replacing the really duff ones and being 5 out certainly does sound like a duff one, so give their helpline a phone, they'll ask you to do a bg test while you're on the phone, compare it to a scan 10 mins later, then fire you a new one for free if it's too far out.
It takes a bit of work to get used to them, but it's time well spent. In the first week I used it, I tested lots, every hour or so, just to get an idea of difference between bg and the ifg (interstitial fluid glucose) which libre is measuring.
Doing it that way, you get a better idea of why there is a "lag" between the two, so you can end up saying, ok, libre says 5 which means bg is probably 6.5, and learn ways to work round that.
Took me about 5 months to be ok bolusing from it, but I got there.
Many people think libre is "plug and play". It's not - it takes time to understand how to read it, but it pays in spades when you learn how to do it.
A part of that is learning how to identify dodgy sensors, they're not all like what you've had, so I'd encourage you to persevere with it, even though your first one has been disappointing.
A lot of us are pimping our libres with small transmitters on top, about £100 for blucon, £160 for miaomiao, they ping readings from libre every 5 mins to an app, so you get full on cgm, hypo alerts, that sort of stuff. You can also feed bg readings into the app, which really tightens up sketchy sensors, although I doubt it would deal that well with one which is 5 out.
Good luck with it, they're well worthwhile once you get used to their quirks!