HbA1c v mmol/l

[qimqim]

I know there is a relationship between HbA1c and mmol/l. For instance, 7% corresponds to an average blood glucose (over the 8-12 week period) of 8mmmol/l.

What I am trying to understand is how one can relate the two readings in order to be significant, if we take into consideration that mmol/l is usually taken while fasting, and that HbA1c reflects an average over 24 hour x 2to3 months, which, obviously, includes high peaks after meals.

So, my question is: would a doctor expect the HbA1c to be higher than the mmol/l results? If so, how much higher on average?

Thank you

qim

 

[totsy]

hya,
my last hba1c was 5.9 and my readings in the previous 3 mnths were between 4/7mmol so it is hard to estimate

 

[qimqim]

Hello Totsy (are you T1 or T2?)

That seems to go along with what I was thinking. 5.9% translates to, approximately, 7 mmol/l.

Your results of 4/7 mmol/l (average 5.5, say) are, I assume, taken while fasting. So, the HbA1c should, normally, by taking into consideration the whole period, including the peaks after meals, return a higher glucose level than morning glucometer readings state. The answer to my question, above, would be that doctos would, indeed, expect HbA1c results to suggest a higher concentration of glucose than fasting blood glucose tests do.

Any scientific comments on this?

qim

 

[totsy]

hya ,
im type 1 so the readings are some fasting, some before meals and some 1hr after,2 hr after

 

[Dennis]

Hi qim,

When you say tests that show mmol are fasting, that is not necessarily true unless you are referring only to a fasting test that your doctor or nurse would do. But whether the mmol test is a fasting test or one that you would do at home, all it can ever show is what your BS level is at that exact moment in time. Whereas the HBA1C covers a period of up to 90 days so will include all the peaks and troughs during that time.

 

[qimqim]

Thank you Dennis. I am fully aware of that.

My question was, and I would appreciate examples, whether HbA1c results are usually, if not always, higher than the average fasting plasma glucose tests taken by a nurse at your clinic or hospital.

Totsy's seems to confirm that, as even with some postprandial tests the average is still much lower than the HbA1c result.

qim

 

[Dennis]

In that case qim, to get a scientific answer maybe you should address your question to a phlebotomist or an endocrinologist. We on this website are fellow diabetics, not scientists.

 

[hanadr]

There is a conversion equation inBernstein, working from averages of MMol/l. Howeverr there is a converter on this web site and conversion tables in several places on the web. Just Google" A1c to Blood glucose Conversion table".
Just be aware that many places quote Mg/dl, not mmol/l The conversion factor from one to the other is 18.

 

[fergus]

This might help clarify things a little, qim.

HbA1c
(%) Avg. Blood Sugar
(mmol/L) (mg/dL)
4 3.3 60
5 5.0 90
6 6.7 120
7 8.3 150
8 10.0 180
9 11.7 210
10 13.3 240
11 15.0 270
12 16.7 300
13 18.3 330
14 20.0 360

I doubt there is a direct relationship between fasting plasma glucose and glycated haemoglobin. There isn't a direct relationship between average blood glucose and HbA1c and any fluctuations above average will have the effect of raising that average, while fluctuations below the average will not lower it. Haemoglobin cannot be un-glycated, so the average is weighted towards higher blood glucose levels.

fergus

 

[qimqim]

Haemoglobin cannot be un-glycated, so the average is weighted towards higher blood glucose levels.

Thank you Fergus

That was a very useful comment.

qim

 

[Trinkwasser]

Haemoglobin cannot be un-glycated, so the average is weighted towards higher blood glucose levels.

Thank you Fergus

That was a very useful comment.

qim

Technical quibble: unlike many other tissues haemoglobin is initially glycated reversibly, so can recover from brief spikes, hence why reactive hypoglycemics and some others show apparently low A1c. After a specific time the glycation becomes irreversible.

Chronic high BG can often be correlated with A1c, at high numbers it tends to track the FBG quite well, at lower A1c the postprandial numbers have more effect, one reason why using it as a diagnostic for diabetes fails to catch many patients.

 

[qimqim]

Thank you Trinkwasser

Chronic high BG can often be correlated with A1c, at high numbers it tends to track the FBG quite well, at lower A1c the postprandial numbers have more effect, one reason why using it as a diagnostic for diabetes fails to catch many patients.

That was very interesting.

Do you know of any site where I could get more information on that?

qim

 

[Trinkwasser]

Thank you Trinkwasser

Chronic high BG can often be correlated with A1c, at high numbers it tends to track the FBG quite well, at lower A1c the postprandial numbers have more effect, one reason why using it as a diagnostic for diabetes fails to catch many patients.

That was very interesting.

Do you know of any site where I could get more information on that?

qim

AFAICR there was a CME paper on Medscape, if you give me a while I'll see if I can track it down

http://cme.medscape.com/viewprogram/17327

this was one

In order to get A1Cs to less than 7%, you need to control fasting, premeal, and postmeal glucose. Therefore, you need to be monitoring these parameters as you go forward. Remember one clinical caveat: when the A1C is very high, above 10%, most of the glucose is coming from the fasting state, meaning the liver is the culprit. As your A1C drops towards the normal range, or the desirable range for your treatment, with an A1C of 8% or 7%, most of the glucose is postprandial. When you select your treatment modalities, that information is important.

You need to register with Medscape but they don't spam you, and there are a whole bunch of useful papers there.

 

[Sweet enough]

Hello Totsy (are you T1 or T2?)

............... The answer to my question, above, would be that doctos would, indeed, expect HbA1c results to suggest a higher concentration of glucose than fasting blood glucose tests do.

Any scientific comments on this?

qim

Definately not scientific but anecdotal!

My recent BS have been very high, Occasional up to 20 mmol and one one occasion 21+
My morning (fasting) bloods were always above 13 usually toward 15 due to dawn phenonomen.
I bought my own strips to discover this. I was so shocked I actually changed Drs as I thought my previous DR wasnt serious about helping me lower BS.
I recently (last week) had a Hba1c that came in at 8.00 If I equate my BS reading to find an average % at hba1c I would have expected a lot more than the 8% ( which yes I know is still way too high)

The thing is ..as a T2 I/we don't check at night when the levels must be quite low to produce an average of 8 % hba1c when daytime readings would suggest a lot more.
Maybe Drs should expect less of a hba1c than strip testing might suggest.

P.S. New GP has increased MR metformin by 500 to 1g x2 per day and added Sitagliptin as well as prescribing strips.
Morning blood sugar today............7.6 mmol I'm beginning to feel like a human again rather than a sugarlump.
Its sometimes worth fighting for you health rather than be told whats good for you by someone who doesnt have diabetes!