# Hba1c calculation formula



## Abc (Apr 3, 2017)

I wanted to know how to calculate your hba1c. I'm using *mmol/L. *I was thinking this was the right formula below. Please help me out

A1c = (2.59 + average_blood_glucose) / 1.59


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## grovesy (Apr 3, 2017)

Welcome.


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## Abc (Apr 3, 2017)

Hi


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## everydayupsanddowns (Apr 3, 2017)

Abc said:


> I wanted to know how to calculate your hba1c. I'm using *mmol/L. *I was thinking this was the right formula below. Please help me out
> 
> A1c = (2.59 + average_blood_glucose) / 1.59



That is similar to one I've seen before, which is:

Estimated A1c = (average_BG+2.52)/1.583

Though you need to bear in mind that any of these are just educated guesses. There is no actual conversion between A1c and fingerstick BG, because the two numbers are measuring entirely different things. The formulae tend to be 'best fit' conversions based on paired empirical data - but of course even those source materials will be potentially skewed by different testing regimes (were post-meal results included? If so when? What about overnight tests etc etc)


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## Amigo (Apr 3, 2017)

I just use this one but my Hba1c has been lower than my 30 day averages because as @everydayupsanddowns  says, nighttime levels etc. skew the figures. It gives some basic parameters however;

http://www.diabetes.co.uk/hba1c-to-blood-sugar-level-converter.html


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## everydayupsanddowns (Apr 3, 2017)

Either of the formulae on this page give very similar results to that page. As far as I can make out I think they are probably using Abc's one, or something very like it, but even at an impossible HbA1c of 100%, they are only a few decimal points out.


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## Abc (Apr 3, 2017)

everydayupsanddowns said:


> That is similar to one I've seen before, which is:
> 
> Estimated A1c = (average_BG+2.52)/1.583
> 
> Though you need to bear in mind that any of these are just educated guesses. There is no actual conversion between A1c and fingerstick BG, because the two numbers are measuring entirely different things. The formulae tend to be 'best fit' conversions based on paired empirical data - but of course even those source materials will be potentially skewed by different testing regimes (were post-meal results included? If so when? What about overnight tests etc etc)


Alright thanks. So your saying its hard to find a accurate answer for a hba1c readings. Could you direct me to any sites that explain these in more detail.


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## everydayupsanddowns (Apr 3, 2017)

The confusion is usually because a Dr or practise nurse has described the HbA1c as an 'average' of blood glucose over the last 3 months. Which it sort of is in a way, but actually is completely different.

The thing about fingerstick BG meter readings is that they only measure your (plasma calibrated) blood glucose reading at that moment. If you checked an hour or two later it would almost certainly be different. And if you check last thing at night and then first thing in the morning neither of those readings can actually reliably tell you what happened in between. You'd have to get up and check overnight if you wanted to know that. Or wear a continuous glucose monitor - but that's a different story.

This is how I think it works...

*What is HbA1c?*
It is a marker of how much glucose has stuck to red blood cells in your blood stream. Red blood cells (haemoglobin) go swishing about your body and as they travel the fluid they are swimming in has a level of glucose in it. Some of that red blood cells get changed by the glucose which sticks to them (they become 'glycated'). And the more glucose you have in your blood stream the more cells are affected. Once cells are glycated they can't change back, so they potter about for the rest of their 120 day lifetime until they get recycled. But importantly the higher your blood glucose, the more haemoglobin gets changed.

What some clever boffin realised, was that by measuring the proportion of the red blood cells that have got glucose stuck to them you had a sort of proxy marker for how full of glucose the blood had been over the last 120 days. And it was a marker that wasn't changed moment-by-moment as the blood glucose altered, it was more stable because of the lifetime of the red blood cells.

Not only that, you could measure it and then track likelihood of complications. And in general terms, the higher the HbA1c, the more likely a person was to have diabetes nasties come knocking at their door.

The weakness of HbA1c is that it can only give a general picture. It cannot tell you how stable blood glucose has been (whether there have been wild swings from high to low levels) and it can't give any detail about when high blood glucose occurred.

That's why many people on the forum are interested in it as a value, but rely more on fingerstick BGs to help them modify their diet, doses and activities to improve BGs day-to-day.


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## Abc (Apr 4, 2017)

everydayupsanddowns said:


> The confusion is usually because a Dr or practise nurse has described the HbA1c as an 'average' of blood glucose over the last 3 months. Which it sort of is in a way, but actually is completely different.
> 
> The thing about fingerstick BG meter readings is that they only measure your (plasma calibrated) blood glucose reading at that moment. If you checked an hour or two later it would almost certainly be different. And if you check last thing at night and then first thing in the morning neither of those readings can actually reliably tell you what happened in between. You'd have to get up and check overnight if you wanted to know that. Or wear a continuous glucose monitor - but that's a different story.
> 
> ...


Thank you very much for your insight into hba1c, blood calculations you've helped


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## Abc (Apr 4, 2017)

If anyone else has anything to add to be my guest


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## jb12 (Nov 11, 2018)

Hi! This thread has been useful because i'm creating a spreadsheet for recording my blood glucose levels. I've been researching the difference and relationship between on the spot BG levels in mmol/l and hba1c. The formula above appears to convert BG levels in mmol/l to hba1c in % (DCCT/NGPS). Is there a formula for converting it into IFCC (mmol/mol), or to convert % to mmol/mol? I haven't really thought about the design yet but i am thinking i might do some statistical analysis on my BGs/hba1c over time in relation to diet and exercise. being able to convert things is a really useful thing and to automate the conversions in excel i need the formulas! This is a good first step though... Thank you!


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## Ljc (Nov 11, 2018)

Hi @jb12 . Sorry I don’t know the formula but thought this graph may help


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## trophywench (Nov 11, 2018)

Well bearing in mind the two tests measure totally different things, and meter readings only reflect that exact minute, you may as well just take a guess.  You're better off considering trends in your BG really, IMHO.

Just because your HbA1c result is a reasonable number is by NO means indicative that your day to day control is good.    I spent over a year with meter readings swinging between HI and LO every single day and my HbA1c result was OK - but I was quite obviously struggling terribly - it just so happened that there were sufficient low readings to cancel out the too many highs.  NBG at all.


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