HBA1C

[Fleegle]

Hi all. Trying to tap into the collective brain of this forum.

Since being diabetic I have been trying to research how HBA1C works and I can find two types of papers on it - one of which talks very high level - it is an average of your blood glucose over 12 weeks by measuring glucose signatures in the haemoglobin - and the second type talks in such detail of biology and chemistry I can not decipher them!

This is what I have concluded so far and I wondered whether people had seen documented evidence to support or deny.
BTW - I understand the problems with people who's blood cells do not last as long as 12 weeks or hang around longer - this is about the how this all is designed to work if you were Josephine average.

- Blood cells are created all of the time and last, on average 12 weeks.
- At time of creation - the cell picks up the current glucose level ???. (I cannot see how in its life the cell could work out average!)
or - how does that work?
- This does not change during its life.
- Once in the lab the blood cells are analysed and from that set they take an average.

If this is true do you think that there is also a figure for low and high - that would be interesting to see to wouldn't it?

I could very well have drawn the wrong conclusions so if you have read differently or my interpretation is wrong please do correct me.

 

[LooperCat]

Once a molecule of glucose has bound itself to the haemoglobin, it stays bound. So all the glucose it collects over the lifetime of the blood cell will be there when they take the sample, the cells doesn’t literally measure the average level. It just collects glucose as it circulates for the (roughly) 3 months, somthe more there is in your body over that time, the more it shows.

 

[Boo1979]

Thats kind of how I understand it but that the result is also inherently weighted towards the more recent BG readings because whilst the average life span of a blood cell is 12 weeks, in any one blood sample if you drew an imaginary divder at say 8 weeks, more of the blood cells will be at the ‘younger’ 0-8 week old end of the spectrum than would be in the ‘older’ 9-12 week old end. Hence averaged BG will be more influenced by the youger blood cells - see, age discrimination gets everywhere!

 

[Fleegle]

Interesting.
Really clever science who ever discovered that needs a noble prize.

 

[ringi]

I read a recent paper that said half the change in BG shows up after 4 weeks in an A1C. So if your BG was a steady 20 for a long time, then quickly dropped to a steady 10, 4 weeks after the drop the A1C will show an average BG of 15.

This is why a lot of doctors who are into low carb will do a A1c 4 weeks after explaining low carb to someone.

(When a bit of glucose bumps into a haemoglobin it sicks on, more glucose there is in the blood more likely a bump is, likewise longer the haemoglobin as been in the blood for, more likely glucose would have bumped into it. Not all haemoglobin lives for 13 weeks, this is a average lifespan, with a lot living for a much shorter time.)

 

[LooperCat]

Like BMI, it’s a very blunt instrument.

 

[Fleegle]

Like BMI, it’s a very blunt instrument.

Why do you say that?
Unless you use a very accurate CGM or blood test really frequently is seems to me to be the best indicator of over all control - no?

 

[LooperCat]

Because it just shows an average, not the lows or spikes, or areas where management needs improving. So your average could be great, but you could be high most of the time with regular hypos that would bring that average way down.

 

[Fleegle]

Because it just shows an average, not the lows or spikes, or areas where management needs improving. So your average could be great, but you could be high most of the time with regular hypos that would bring that average way down.

Ok I think I agree with you.
And if those highs and lows are not at times you are measuring you would never know anyway.
For example, liver dumps, exercise.

I used a freestyle and found that eating 1h 2h was the least of my problems

And I guess - a bit like BMI, although an absolute isn't very useful - if the trend is going up or down that is in itself interesting.

 

[miahara]

if the trend is going up or down that is in itself interesting.

Yes it's the trend that I find most informative. It gives me a pretty good picture as to how well or otherwise my diabetes is being managed.
During the intial months after diagnosis I self tested regularly and after a while got to know pretty well how different foods affected my BG. I've now stopped pre and post prandial testing and only do a fasting test a couple of times a week, just to keep an eye on things.
I'm off medication at present but if after my next test my GP suggests I get back on them I'll revert to more frequent testing for a while in order to monitor the effects of the meds

 

[Bluetit1802]

Why do you say that?
Unless you use a very accurate CGM or blood test really frequently is seems to me to be the best indicator of over all control - no?

It is a reasonable tool for initial diagnosis, but as for being the best indicator of good control I do not agree. The best indicators are the CGMs and the Libre as you say, plus very regular finger pricking if you don't have a CGM/Libre. The HbA1c has come under heavy fire because of the fallacy of average - 2 people with identical HbA1c results can have very different levels of control. One can have a smoothish line with a few bumps here and there, the other can roller coaster up and down. Then there are the anomalies of people with non-standard red blood cells - and there are many such people. I just use my review HbA1cs as trend markers and something to keep my nurse happy. I certainly don't use them to measure my personal control.

 

[Brunneria]

Why do you say that?
Unless you use a very accurate CGM or blood test really frequently is seems to me to be the best indicator of over all control - no?

Different people have different rates of glycation - and it is the personal rate of glycation that determins the accuracy of the HbA1c.
Slow glycators get higher test results, not because their blood glucose was higher over the last 2-3 months, but because their red blood cells have been hanging around for longer, and have accumulated more gluocse.
http://journals.sagepub.com/doi/pdf/10.1177/000456329903600408

and then there are iron levels...
anaemia will mess up HbA1c results too, requiring a different type of test to be used - which many doctors have never even heard of!
https://www.diabetes.co.uk/news/201...ted-through-hba1c-due-to-anemia-97409751.html
and
http://www.gpnotebook.co.uk/simplepage.cfm?ID=x20071228072816056327

 

[miahara]

@Bluetit1802 . I'm obviously a bit ignorant, but what's a CGM please? Guessing something to do with glucose meter.

 

[Bluetit1802]

@Bluetit1802 . I'm obviously a bit ignorant, but what's a CGM please? Guessing something to do with glucose meter.

A continuous glucose monitoring system. Some of the T1s on here use them.

 

[kokhongw]

This paper also list out some of the considerations when using HbA1c as a diagnosis tool for diabetes.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3632159/

Limitations of HbA1c
http://www.bmj.com/content/348/bmj.g2867

Then of course there is the limitation of considering only the glucose toxicity and overlooking the insulin toxicity that is common among obesity related T2D.

It is rather incomprehensible that a well known condition or pre-condition such as hyperinsulinemia/reactive hypoglycemia should be left completely untreated until it has progressed pass the point of complete glucose tolerance failure.