Libre 2 Plus Estimated A1C

Hi All,

I'm currently on holiday in Turkey this week (and missing the dreadful weather at home in the uk fortunately).

Quick background, I was diagnosed in Jan 2021 when I was 20 stone. It took a while to get used to it, but within three months I was 70 and then down to 58 then 48 and then 38 in the last blood test in August 2025.

I have lost a lot of weight and I'm now 13.5 stone and I am very strict with myself trying to keep the carbs as low as possible. I think I eat less than 100g a day in carbs. I really don't eat much at all compared to what I used to. I have breakfast of eggs and bacon usually, sometimes I skip lunch and then have dinner of say 2 pork chops with salad. I don't ever eat anything to do with potatoes.

I have had a test Libre 2 about a month after my last blood test which I found very very useful. After the 14 days it said my estimated A1C was 33.

As I am on an all-inclusive Turkey holiday (I thought this was a good idea as it is all buffet type food so I can just have things like fish, cheese, salad, chicked, beef etc.) I have been eating quite a lot more than I would normally have.
I decided to buy a libre 2 to use while here as I wanted to make sure I wasn't getting high figures when eating food I wouldn't normally eat.

It's been fine all the time I've been here so far and the most it had gone up to in the last couple of days was 7.1 but very quickly (within 40 minutes shot back down to around 4.9 - 5.2. I started to get a bit more adventurous and had two slices of cheesecake (1 chocolate) which I really enjoyed. My BG went to 8.6 but then, again, came down within about 40 minutes to 5.2 - 5.6. Today I had another two slices of cheesecake with lunch and another two slices with dinner (and had two scoops of chocolate ice cream at 3.30pm).

Again my BG went up, this time to 8.9 but then came back down very quickly again and stayed in the low 5s. I have been drinking about 10 0.3L beers each day as well each day and that doesn't seem to raise my BG much at all.

The device has now estimated my A1C to be a staggering 29mmol (4.8%). Do you think that this reader could be faulty? surely I can't be anywhere near 29. I am a bit confused - i would be really pleased but I am completely suspicious of it. Unfortunately I don't ever prick my finger as I haven't got that type of testing kit and I've always been a little bit scared of pricking myself - I find the stick on Libre to be great and not at all painful.

Has anyone else ever had a faulty one, or one that reads far too low? It can't be completely faulty as it does go up after eating.

Thanks for the responses, it is appreciated. It makes sense that it seems to be showing the figures lower - but as you say it is showing me that my BG does come back down a lot quicker than it was when I first used the test one.

I thought 29 was a bit strange - however, with the test libre a couple of months ago it would show 33 (when I was about 38) so I guess that 29 means I am lower than I was but just not as low as that. I've enjoyed the chocolate things the last couple of days but to be honest not as much as I thought I would so I won't be having them again. Next week I'll be back on the "wagon" though I actually really enjoy what I eat at home now. My life has got so much better in some ways since getting divorced last year - it's very sad in some respects and I miss my ex-wife a lot but there is no getting away from it that I am happier now. I have found it much easier to lose weight and to restrict eating when happier - I guess I now understand when people talk about comfort eating.

Bill_St said:

It is important to recognise that laboratory blood tests are not absolute values. A test result of 33 could actually indicate quite a wide range of actual value - perhaps as low as 27 even to 95% probability. Perhaps as high as 39.
The BMJ gives a useful tool as guidance for doctors to show the variability of blood results. Running it for 33 gives this result. Blood tests just provide a single result and that has variability. Libre is based on many readings. Repeating blood tests could show quite different values for each test.

It should also be recognised that Libre is shown to Play Safe, perhaps to satisfy the regulators, and to avoid the dangers of Hypo it is seen to give lower values in the Low ranges.

Also the blood test is not linear over 90 days. It is based on cell “death” rates so actually is more dependant upon the latest 30 days than the first 30 days…. Libre is an arithmetic average so can be across the whole measured range up to 90days; however if only worn for less then it will be averaged across that range.

HbA1c has been a useful and easy estimation for many years but now most specialists believe that Time in Range TiR, is much more useful to manage BG levels now that CGM allows an easy display and calculation of that value.

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Thanks for that, I find that quite interesting. I had thought that the blood test was more dependent on the later days than the first days - one of my friends goes on a crash diet in the last couple of weeks before her blood test and swears it makes a difference to the blood test, haha, though she says that very tounge in cheek.