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HBA1c totally different to Libre 2 result??? - Advice needed

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Noggin11

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I've just had my latest HBA1c result back and it's significantly different to the predicted result from my Libre2+ sensor report (I've been using the Libre2+ continually now for 5 months).

The Libre estimates 49 mmol/mol for the last 3 month period but the HBA1c has come back as 57!

Does anyone have experience of their Libre value either correlating with oir being different to the HBA1c, and if so by how much?

This difference has really knocked me and raises serious doubts about whether the device is even worth having,

Thanks
Viv
 
Welcome to the forum, Viv

Yes, it is common to see variations between the Estimated HBA1c from Libre and the real blood test. There are a number pf reasons for this but I think the main one is that they are measuring different things so Libre can only estimate.
My Libre estimated more than 20% lower than the blood test. But that did not make me think the Libre wasn't worthwhile. It has been fantastic for me. But it does depend upon what you are using it for. As I have Type 1, I suspect our needs are different.

There is another thread that discusses these differences which you may find useful:

Libre HbA1c v Actual HbA1c​

 
A number of reasons:

  1. Libre makes an estimation based on average readings from the sensor, but hba1c is an actual measure of glucose on blood.
  2. Libre is using readings from fluid in the skin, not blood, and they can be different due to rapid changes in blood sugar and things like 'compression lows' (i.e. sleeping on it.)
  3. Lifetime of blood cells is different and this may dictate the result (Sensor has no way of knowing this.)
  4. Over the two weeks, the sensor readings tend to be less accurate over time, especially towards the end of the the life-span (Due to 'muck' on the filament.)

I believe it's also quite common for the estimate to be lower in people with good control or in remission.
 
My Libre HbA1c estimates have almost always been lower by 3-4mmols than the actual result but that ties in with Libre usually reading lower than my finger prick readings, in my experience. Plus any compression lows during the night will also artificially reduce it's estimate, although I rarely get those. Surprisingly my last Libre HbA1c prediction earlier this year was spot on with my actual result.

If you have anaemia, that can artificially inflate your actual HbA1c but I am not sure that it would impact your Libre readings and hence it's HbA1c prediction, so that could perhaps also account for a dramatic difference IF you were anaemic. I can understand you being rather disappointed.

Do you also finger prick or have you been solely relying on Libre. Most of us would not recommend that because it isn't always reliable and you have to be able to double check it at times.

How do you use the Libre to manage your diabetes? Would you be better off spending less money on before and after meal readings with a BG meter instead. We all know Libre is very expensive to self fund and unless you are on insulin then I don't think it is cost effective to self fund it long term. Best to use it intermittently to gain useful data about how you respond to foods and then have a few weeks without, where you consolidate what you have learned from that sensor and the meals it tested and then a few weeks later, perhaps use another one to see if you can fine tune your diet and exercise a bit more.

Obviously a slightly different matter if you are on insulin.
 
Libre isn’t measuring a1c, it doesn’t look at your blood whatsoever. It’s a rough estimate based on average glucose only. Your actual a1c is what your blood shows has happened over the last 3 months.
 
Noggin11 said:
I've just had my latest HBA1c result back and it's significantly different to the predicted result from my Libre2+ sensor report (I've been using the Libre2+ continually now for 5 months).
Click to expand...
If you've haven't seen this it's worth a read:-.

www.diabetes.co.uk

Continuous Glucose Monitoring - What is CGM, Control, How To Get a CGM

With a blood glucose meter, you use blood to do the test whereas CGM is continuous glucose monitoring. Read about how they work and getting one.
www.diabetes.co.uk www.diabetes.co.uk
 
1745585645713.png

From my point of view the HbA1c result is a guide to how I am doing.

It was just off the scale at 104 (in the danger zone). Now it's in the 30-40 zone (normal) as a result of a healthy diet (mainly protein and non-starchy vegetables).

If it strays into the 40-50 prediabetes zone (indicating fatty liver, hormone dysregulation, insulin resistance ...) I will get a CGM to measure which foods are causing BG swings, meal by meal. Then I'll know more about how to adjust my diet.

Meanwhile I keep an eye on my weight.

I also monitor my nutrient intake using Cronometer. People say it's not necessary to count carbs, but I find it useful to keep an eye on everything else including iron, potassium, calcium, folates, vitamins and so on.

Horses for courses.
 
Here is a list of contributions by members showing libre predictions vs actual HbA1c taken from the thread mentioned by @helli. I have added yours.

Libre Actual Difference
45 47 -2
51 47 4
41 39 2
35 45 -10
38 47 -9
48 46 2
39 44 -5
48 56 -8
46 58 -12
33 38 -5
45 54 -9
34 37 -3
42 36 6
40 46 -6
49 59 -10
48 50 -2
51 48 3
44 44 0
49 57 -9

As you can see there is a tendency for the libre to underestimate and a 9 difference is far from unusual. The strength of the Libre is in tracking short term changes to look at the effects of different foods and to check and adjust dosing for those using insulin. It is of limited value when it comes to predicting HbA1c it would seem.
 
My Libre has estimated my hba1c at 44 for the last three years. I’ve been between 50 and 52! I’ve got my diabetes review next month, I’m not expecting it to be 44 which it is showing again as I’ve just looked. I think it’s stuck!
 
Ah sorry you’ve been a bit disappointed by the estimate provided by Libre. I always found it tended to estimate quite a bit lower than my lab results too.

One of the challenges is that this is biology, not maths. There isn’t a mathematical conversion from HbA1c to sensor glucose values. But what they can do is find a ‘best fit’ formula with pairs of empirical data, and give an estimate. Further than that, people ‘glycate’ red blood cells at slightly different rates. And it’s the glycated haemoglobin that the A1c is measuring. So depending on how eagerly your body glycates red blood cells at a given glucose concentration, you may have a higher (or lower) HbA1c level than another person with an identical sensor glucose average over 90 days.

I hope you can quickly bounce back from this upset.

I’m not entirely sure what formula Libre uses, but Dexcom offers their GMI (glucose management indicator) with the following:

GMI mmol/mol = (4.70587 x CGM average mmol/L) + 12.71

With a few more Libre estimates / sensor glucose averages you may be able to tweak that formula so that it provides better estimates for yu as an individual. @Docb seems to be pretty handy at this sort of number juggling.
 
I seem to be fairly consistently the other way where the Libre over estimates. It was predicting 48 which after a call today turned out to be 45 which follows the previous review of a prediction of 50 vs and actual 47.
 
Out of interest, for the example given in the OP, libre estimating 49

49 is 6.6%

Libre formula says average bg of 7.9

By the dexcom formula @everydayupsanddowns gave an average bg of 7.9 would get you an a1c of 50

Going to an extreme an average bg of 20 would by dexcom get you an a1c of 107, and by libre get you 14.2% which is 132

So libre and dexcom arent using identical formulas, and they give results in different metrics. But libre and dexcom probably give very similar estimates hba1cs for most people, with libre estimating slightly lower at more normal bgs and libre far overestimating dexcom for extremely high results.

Unless I’ve done my maths wrong.
 
Brilliant information everyone. Thank you so much. I was hoping to use the numbers from the Libre to estimate hba1c and track my progress, but it seemed that wasn't going to work. However, the guidance here around adjusting for your own body and using a personalised calculation instead of the libre report may have rescued that plan. As it turns out, the graph in the first linked thread works perfectly for me so I can use that equation to do my calculations.

Thanks everyone!
 
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