HBA1C doesnt reflect extensive CGM and Finger Testing

[Damian1991]

Hi,

I have looked to improve my blood sugars for the last 5 months with great results on my libre 2 and finger prick machines.

I have recently had my hba1c at the doctors and it came back as 50 (6.7%) which I believe equates to an average of 8.1mmol/L on the finger prick.

According to my CGM and glucose monitor I should have been noticeably lower than this.

This makes no sense to me and doesn't tally up with my extensive testing on both Libre 2 and finger prick machine.

HBA1C - 50 (6.7%) which would be 8.1 mmol/L
Libre 2 (90 days) - 45 (6.3%) which would be 7.5mmol/L
Finger prick (Freestyle Optimum Neo) - 40 (5.8%) which would be 6.6mmol/L

Finger prick is over 30 days with a sample of 283 (I truly believe this has been spaced out well throughtout the day at the appropriate times up to 10 times a day)
Libre doesnt show any high spikes throughout 8 hours of sleep on the night and my waking finger prick is consistently good in the 5's and sometimes 6's

My Libre tends to track higher than finger prick alot of the time, even when I am in the high 3's the libre will tend to show straight arrow in low 5's.
If i am in the 5's and 6's on finger prick libre will tend to show 7s and sometimes 8 - I double check the finger prick with my old freestyle optium machine - The 2 finger prick machnies often show little discrepancy between each other.
This is during very stable times as well over the course of hours. My variance has been very low so it is not like my sugars are bouncing all over quickly either which the libre might not pick up.

I have been militant with this, and I genuinely just don't understand where an average of 8.1mmol/L from the lab test has come from.

Firstly, am I interpreting all of the above correctly?
Secndly, what do I believe? According to my libre and finger pricks I feel like theres not much more I can do.

I have always trusted my finger prick readings above anything but now I just don't know.

 

[TheSecretCarbAddict]

I think there are a couple of important items to understand.

HbA1c, CGM, and glucometers measure very different things, and while formulas have been developed to translate values between these tests, they are only estimates. HbA1c measures how many glucose molecules are attached to your red blood cells. As these cells tend to live 3-4 months, it is generally accepted that the glucose concentration here reflects your average glucose levels over that period. Glucometer measures your blood plasma glucose levels - it works a little bit like urine strip, blood reacts with chemicals in the strip, strip changes colour based on the current level of glucose in your blood and then machine reads it and displays a number. CGMs measure glucose level in your interstitial fluid and try to approximate this to your blood plasma glucose levels through an algorythm.

All these devices, whether professional or consumer, come with their own margin of error and testing conditions, which can also affect the outcomes of these tests. Lab tests are generally considered a gold standard, with consumer devices being quite precise but more indicative of your actual blood glucose levels.

 

[catinahat]

The Hba1c is not testing the same thing as your Libre or glucose meter, plus each testing method has it's own percentage of accuracy, the finger prick test is +/-15%, don't know what the Libre is but would think it's similar to the finger prick, and the Hba1c is +/-6% I think?
The meter and Libre measure the glucose in your blood, some of that glucose binds to the protein that carries oxygen in your blood (Haemoglobin) so the Hba1c measures glycated Haemoglobin.
It's thought of as an average because the higher your blood sugar has been over the life of your blood cells, more of your Haemoglobin will be glycated and the higher your Hba1c will be.
It's not really an average though because how long do your blood cells live? They usually hang around for about 12 weeks, but could be 11 or 13.
The comparisons between finger prick results and Hba1c are really just rough guides.
It would be a miracle if the averages from 3 different tests, all with different margins of accuracy, one of them not a true average and measuring something different from the other 2, were the same.
The Libre and your meter tell it as it is, as far as the technology available to us is able to.
The Hba1c is just a useful measure for doctors to assess how we're doing.
Personally I think that all of your results show that you're doing a pretty good job