Why the big difference between the HBA1c and daily readings?

[PickledPepper]

I know HBA1C is a 3 monthly average of your bs level.

What I don't get is that I tested very, very intensively during my first 3 - 4 months and have quite a good knowledge of the figures I was getting. For a while there they would be quite high (double figures) until I sorted the diet out through experimentation. Even after that they still hung around the mid 6 mark most of the time. There is no way I think the average of those figures would be near what my HBA1C was last recorded at.

Now looking at all those figures I'm quite surprised at having a low HBA1C (5.8). I expected it to be higher?

For the sake of understanding - any explanation people?

 

[Hobs]

Re: Why the big difference between the HBA1c and daily readi

HbA1c is expressed as a % and your home testing meter will displayed in milli-moles per Litre in the UK . The two figures should not be compared and this should haved been explained to you by your diabetes care team/person.

 

[Bigglesworth]

Re: Why the big difference between the HBA1c and daily readi

You can convert meter readings from HbA1c and vice versa. Number of sites have a calculator. Worth also reading the HbA1c methodology and various websites offer good explanations. Its not a simple arithmetic average.

 

[daisy1]

Re: Why the big difference between the HBA1c and daily readi

But it just so happens that 5mmol/l converts to HbA1c 5% as well , or near enough.

 

[PickledPepper]

Re: Why the big difference between the HBA1c and daily readi

That should've been a HBA1C of 5.8 in the original post - not '5 point smiley with cool shades on'

Just so you all know!

 

[cugila]

Re: Why the big difference between the HBA1c and daily readi

There is a Bg level to HbA1c converter on this websites Community pages here.......

http://www.diabetes.co.uk/hba1c-to-bloo ... erter.html

The lower the level the closer the result will be to your actual HbA1c........as the numbers get higher so the difference is greater. If you put in a whole number you will get a result in the new numbers mmol/mol. If you enter a number with a decimal point then it gives the old numbers ?
I have no idea why that should be though.

 

[PickledPepper]

Re: Why the big difference between the HBA1c and daily readi

Hang on?

I thought HBA1C was an approx 3 month average? Then I read this on the above link:

The HbA1c level in your blood indicates what your average blood glucose level has been in the past 4 weeks, approximately.

???

3 months to a month......

Oh well, that would explain the lower than expected result as things started to get a bit more under control after 2 months of testing and experimenting with diet.....

If you put in a whole number you will get a result in the new numbers mmol/mol. If you enter a number with a decimal point then it gives the old numbers ?

You completely lost me there?

What was shocking was my mmol reading (converted from the HBA1c) when I was first diagnosed...a stonking 23.17....

Wowsers!

 

[hanadr]

Re: Why the big difference between the HBA1c and daily readi

the 2 measurements are reading quite different things. Your meter reads the amount of free glucose circulating in your blood. the units are millimoles per litre. One mole of glucose weighs 18 grams so a millimole weighs0.018grams[please check my arithmeticfolks!]
Hb stands for haemoglobin.
Haemoglobin 1c is one type of haemoglobin, where glucose has irreversibly bonded to it. the more circulating glucose you have, the higher HbA1c will become. It's expessed as a percent of your total haemoglobin. Hence if your haemoglobin is low qas in anaemia, your Hb A1c will show high.
Non-diabetics have a Blood glucose value of about 5mmol/l MOSt of the time and an HbA1c around 5% .
Even these n=mbers are thought to be higher than the ideal and being averages, they include numbers from undiagnosed diabetics and pre-diabetics.
Hana

 

[cugila]

Re: Why the big difference between the HBA1c and daily readi

PP
Stick a whole number in the converter and it will give the new mmol/mol numbers. They are changing. There is a conversion table on the forum.

If you put say a Bg of 6.6 it will give the older HbA1c number _ Try it and see. You should get your results in both numbers. They both mean the same things just in a different measure that's all.

 

[Cliff2]

Re: Why the big difference between the HBA1c and daily readi

The difference arises because the HbA1c and your meter are measuring completely different things. The numbers are only close because of the mathematical way their units are expressed.

The HbA1c measures the amount of glycosylated haemoglobin in the A1c fraction of your blood. That result is then expressed as a percentage of total A1c fraction haemoglobin.

Your meter is measuring the amount of glucose in your blood at a particular point in time (most meters then convert that automatically to the amount in your blood plasma so it correlates with the way hospitals labs do it which is to measure glucose in the plasma rather than the blood). Glucose is expressed in units of millimoles per litre (mmol/l) which is completely different from the HbA1c percentage.

There are ways of matching the two up and estimating your HbA1c from your meter average but it's not an exact science because the formulae (and there are many of them) are all empirically derived. That means that they are not devised from rigid scientific laws but rather from looking at thousands of results from real patients and working out a formula that's a best fit with the results.

For those of you that are comfortable with figures, the formula I use is BG = (1.583xHbA1c)-2.52 which if you rearrange gives HbA1c = (BG+2.52)/1.583. It predicted my HbA1c to within 0.1% the last time. It's at it's most accurate when you are averaging BG readings from your meter over the last 90 days with a good spread of fasting and pre- and post-meal readings. It really is a very rough and ready conversion though.

 

[Sid Bonkers]

Re: Why the big difference between the HBA1c and daily readi

The way it was explained to me:

Glucose attaches itself to red blood cells in the body, blood cells live for 120 days (approx). As millions die ever second, millions are generated which new glucose molecules are attracted to.

So when a test is done to measure the amount of glucose in the blood the newer red blood cells will have more glucose attached than the older red blood cells which have been feeding the bodies energy requirements for up to 120 days (approx)

So although the Hb A1c is an average of the last 4 months glucose levels it will always be biased in favour of the newer blood cells so it can be affected by your last months control.

Hope that makes sense, as my head hurts now

 

[phoenix]

Re: Why the big difference between the HBA1c and daily readi

(just to repeat what SId said... he posted before me!)

glucose bonds to the haemoglobin (in red blood cells). This is called glycation . The higher the glucose and the longer the blood cells are exposed to high glucose the more glycation occurs.

The average lifespan of a red blood cell is 120 days.There will always be a mixture of old and new cells present in the blood. Older cells will have been exposed to both older glucose levels and more recent levels. New cells only to the more recent levels so there will be a greater influence from the more recent glucose levels. One source says that half of the HbA1c level may be a result of the last months glucose levels, a quarter from the previous months and a quarter from 2 months ago.
http://www.embeediagnostics.com/features/hba1c.htm
certain types of anemia produce lower levels as the cells are being destroyed more quickly. People with end stage renal disease and sickle cell disease will have low levels. People who have had a blood transfusion in the last few months will also get misleading results.

There are several HbA1c to estimated average blood glucose calculators on the net and they give different results , The one on this site seems to give a significantly lower figure than the one on the American Diabetes Association site. I know the ADA one has been devised in the last year or so as a result of recent international research.
http://professional.diabetes.org/GlucoseCalculator.aspx

 

[PickledPepper]

Re: Why the big difference between the HBA1c and daily readi

Wow!

Thanks for the explanations folks.

All is now explained.

If your theories are correct I should see another decrease at my next test in 6 months time (providing I generally maintain discipline which is not guaranteed).

Seems quite a wait. Does anyone else have 6 monthly tests only?

 

[jopar]

Re: Why the big difference between the HBA1c and daily readi

The adverages on your blood glucose meter can be helpful to determin whether your over-all control is going up or down a rough guide to see if you are staying on track..

If you are testing enough on a daily bases on the same meter, you can actually gauge your HbA1c out-come.. I know with my meter that my HbA1c's is comes out about 1.4mmol/l than my 90 day..

Using this information and the converters, I'm on track to a HbA1c in the 5's who said you've got to avoid carb to maintain good control...