Help with terminology and converting numbers please.

Jan1956

Jan1956

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So, reading that a Hba1c of say 48 mmol/mol is equivalent to 6.5 % ?
In my case my Hba1c of 55 is therefore 7.2%
My question is when I’m taking my finger prick tests the results are recorded as mmol/L
So, when I get my average readings on a contour plus monitor of say 8.2 mmol/L I’m
wondering if this the same as having 8.2 % on a Hba1c test?
If so my Hba1c average is likely increasing?
However,
On The Libre 2 seems to calculate an average Hba1c
Is there a a calculation formula I could use with my average finger prick results ( mol/l ) to give me an indication of my future HBa1c reading?

Thank you
 
Hi @Jan1956. The HbA1c test and the blood glucose monitor are measuring different things and the fact that the numbers are a bit similar is coincidence. You cannot translate one to the other but if one is consistently high, then the other is likely to be high. I contend you can do better if you collect lots of finger prick results and your HbA1c results and are a bit of a dab hand at spreadsheets and statistics but it is one for the nerds.

Think about it like with your car. Your MPG and the speed you see at any time on the speedometer are related. The faster you drive then the lower your MPG but you would not dream of converting one to the other with any precision.
 
You aren’t the first to have wondered this @Jan1956

There are associations between HbA1c and fingerstick readings, but there is no direct mathematical conversion possible, because the two are measuring very different things.

The % and mmol/mol are different expressions of the same HbA1c test, so these can be converted.

However fingerstick checks are just a ‘moment in time’, and even a large number aggregated as an average will depend on how accurately the timing of the checks picks up the rises, falls, and range of glucose variation.

Sensors that read 24/7 try a ‘best fit’ with empirical data of paired average fingerstick glucose vs HbA1c, but these are only a guide. They aren’t always an accurate prediction.

And @Docb types faster than I do!
 
There is a rough conversion chart which shows HbA1c in both % and mmols/mol and average Blood Glucose in mmol/L and I have a feeling @Martin.A has a link to it and will hopefully post it now I have tagged him, as I couldn't manage to link it. There is no direct conversion, but it gives you a rough idea and will hopefully set your mind at rest a bit that things are not going backwards.
 
Docb said:
Hi @Jan1956. The HbA1c test and the blood glucose monitor are measuring different things and the fact that the numbers are a bit similar is coincidence. You cannot translate one to the other but if one is consistently high, then the other is likely to be high. I contend you can do better if you collect lots of finger prick results and your HbA1c results and are a bit of a dab hand at spreadsheets and statistics but it is one for the nerds.

Think about it like with your car. Your MPG and the speed you see at any time on the speedometer are related. The faster you drive then the lower your MPG but you would not dream of converting one to the other with any precision.
Click to expand...
Thanks for explaining this with the helpful analogy. I can see how they’re inter related and hoping that my next Hba1c will be lower than a 8.2 % average then
 
everydayupsanddowns said:
You aren’t the first to have wondered this @Jan1956

There are associations between HbA1c and fingerstick readings, but there is no direct mathematical conversion possible, because the two are measuring very different things.

The % and mmol/mol are different expressions of the same HbA1c test, so these can be converted.

However fingerstick checks are just a ‘moment in time’, and even a large number aggregated as an average will depend on how accurately the timing of the checks picks up the rises, falls, and range of glucose variation.

Sensors that read 24/7 try a ‘best fit’ with empirical data of paired average fingerstick glucose vs HbA1c, but these are only a guide. They aren’t always an accurate prediction.

And @Docb types faster than I do!
Click to expand...
Thank you for taking time to reply and for explaining this. Yes it makes sense when you explain that finger print testing is more random so averages and conversion to Hba1c (if this were possible) would be fairly inaccurate.
My Libre free trial monitor arrived yesterday so I’m just starting the two week trial but I’m already finding the results compared to my finger print testing are hugely different at times. Maybe it will settle down in 24 hrs.
 
rebrascora said:
There is a rough conversion chart which shows HbA1c in both % and mmols/mol and average Blood Glucose in mmol/L and I have a feeling @Martin.A has a link to it and will hopefully post it now I have tagged him, as I couldn't manage to link it. There is no direct conversion, but it gives you a rough idea and will hopefully set your mind at rest a bit that things are not going backwards.
Click to expand...
Thank you @rebrascora
 

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I think I would just forget the % because that is the OLD units for the HbA1C result which is now mmol/mol., 48mmol/mol and above for a diabetes diagnosis. It was changes so people would not confuse and compare to finger prick test readings which are in mmol/l./ The confusion was because mmol/l numbers are similar to % numbers
 
Jan1956 said:
Thank you for taking time to reply and for explaining this. Yes it makes sense when you explain that finger print testing is more random so averages and conversion to Hba1c (if this were possible) would be fairly inaccurate.
My Libre free trial monitor arrived yesterday so I’m just starting the two week trial but I’m already finding the results compared to my finger print testing are hugely different at times. Maybe it will settle down in 24 hrs.
Click to expand...

Libre is continually measuring glucose in interstitial fluid, and has an algorithm to convert that to reflect blood plasma values. There can be a delay in sensor glucose coming into line with fingerstick glucose, and some sensors can take a while after insertion to settle.

@helli wrote a helpful reply once before, which was snipped out and made as a sticky for people to refer to
H

Thread 'CGM limitations and precautions'

Moderator Note: This helpful reply was copied from another thread as it details some of the commonly experienced limitations of continuous glucose sensors.

MarinaDE said:
My blood sugar has been in perfect range for days now, but although I haven't changed anything, I'm starting to get very short periods of hypos while I sleep and this morning I had a hypo alarm.
Click to expand...
If these are very short periods of lows and occur overnight, they are more likely to be compression lows - when pressure is applied to a sensor, it will report a false low. The reason I say this is more likely to happen at...
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Hope you find the Libre a source of useful trend information. Try not to worry too much about differences between sensor glucose and fingerstick glucose. Both systems have ‘margins of error’ so some variance is almost inevitable.
 
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