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Just a thought/question.

D

Defren

Well-Known Member
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The HbA1c test is to give us an idea of how our BG's have been doing in the previous three months. I am sure I read somewhere, that the life of each cell is around 90-100 days, hence why the HbA1c is used. In that time glucose can stick to individual cells, and perhaps cause slightly higher readings? Would that assumption be about right?

Once we begin to control our condition, in whichever way is best for us, and see our readings drop, does suggest that as new cells are being produced, there is less glucose that sticks to these cells?

If the above is right, and I have no idea if it is, then should we look at the real starting point from when we have an HbA1c test done, after at least 90-100 days after we begin to control our diabetes? That would be the time when our cells are at their least clogged with glucose?

I need to quit reading, my head is spinning!
 
You're pretty much spot-on. Except thatt the life of a red corpuscle [they are NOT TUE cells] is about 120days. Hence if we havvee an annual HbA1c, there's very little evidence of what was happening less recently than that.
that's why some authorities advise HbA1c should be done about every 3 months.
My health centre does them every 12 months, so I did a deal with the DSN and get it done every 6 months. Still not frequent enough for my beliefs, but less time to have trouble in.
Hana
PS never stop reading, but always evaluate what you read.
 

Thank you Hana. I truly don't have a scientific mind, so what may appear to me to be logical, in science is way off beam. I read so much, and then all of a sudden, something I have read in one place, ties with something else somewhere else. Like my question above, I then get an idea in my mind of what may be right, and so ask.

So, as I dd get the above almost right, should I wait until the end of this month when my next HbA1c is due, and work from that opposed to the figure at diagnosis, in other words, completely ignore my diagnostic number?
 
HbA1c is a weighted average. It is affected far more by recent blood glucose levels than those 120 days ago, because there are many more cells alive and exposed to recent glucose levels than older cells.
Glucose levels from the last 30 days contribute 50% to the final HbA1c whereas glucose levels from 90-120 days ago contribute only 10%.
HbA1c can increase or decrease relatively quickly with large changes in glucose; it does not take 120 days to detect a clinically meaningful change in HbA1c following a clinically significant change in AG
Click to expand...
http://www.ngsp.org/A1ceAG.asp
http://www.clinlabnavigator.com/Test-In ... n-a1c.html
This blogger has tried to show what happens as a diagram. (it might help explain... not sure)
http://www.diabetesdaily.com/forum/blog ... -sugars-do
 
As Phoenix said, recent blood glucose levels have a much bigger effect in our HbA1c than older ones. Like a lot of geeks, I use a spreadsheet with a graph to plot my BGs and work out what I think my HbA1c would be at any time. I use a calculation taking 85% of the last month averages, 15% of the previous month and 5% of the one before that. It's normally about right allowing for meter errors. This is of course based on a rolling 3 month period.
 


That's interesting Phoenix that the last 30 days represents 50% of a Hba1c test :think:
 
phoenix said:
Glucose levels from the last 30 days contribute 50% to the final HbA1c
Click to expand...

Out of interest Phoenix, I've seen a recent study that suggested that even more is attributable to the last month, up to 80%, with even that being heavily weighted to the last 2 weeks. As a model, that seems to fit roughly with my experience. With a steady half-life figure, i'd have thought it would be a straight fixed calculation but apparently not.
 
Interesting.
Just anecdotally, I had a virus for 3 weeks during February and much higher overall levels. I then got back to normal for a couple of weeks before my HbA1c. I really expected a rise so was quite surprised that it was just 1% higher than previously.
 
Backs up the thinking. We've actually got a one month test in reality to a large degree, despite always having it referred to as 3 months.
 
My meter is pretty accurate due to the amount of testing I do everyday, I can rule out hidden spikes between testing, as if this was the case I would expect to see a greater difference between my meter and HbA1c result..

My meter 90 day average always comes in 0.3 above the HbA1c blood test, last one HbA1c 5.8% and my meter read 6.1% my meter also does, 60 days, 30, days 14 days and 7 days averages as well... looking at my present readings there's only 0.2 either way of 6% (90 days)...

Now because of the frequency of testing I do, I know it's unlikely that my BG is spiking scarily high, due to very limited times I go below 4mmol/l so I'm not having hypo's masking high's etc..

Now it's my opinion that the HbA1c's can tell more and is more reflective towards T2's who are either following diet controlled or non-hypo inducing medical such as insulin.... Than it can for a T1, who's hypo's masks the high's or T2's who are taking hypo inducing medication..

So if a T2's says there HbA1c is 5.3% is very likely that there BG's isn't causing too much of a problem, and that they aren't suffering from harmful spiking..

How this should reflect to how often they should have an HbA1c's done, well I would say every 3 months,,, Perhaps longer if they have a back up of a meter...
 
Not Quite sure about the point Jopar. You say your meter is very close to your HbA1c at 6.1 to 5.8, but of course they're different units, and an HbA1c of 5.8 actually equates to an average blood plasma (meter average) reading of 7.2mmol/l . This implies either your meter isn't as accurate as you thought, or you are indeed having spikes outside of your readings fairly consistently to take your overall average from 6.1 to 7.2.
Have I Misunderstood your point?
 
Can I just add here, the point of my question seems to be missed. I'm not interested in meters matching HbA1c levels etc, I am asking, is it best to avoid your diagnostic test (in my case 7.0) and focus on the second and subsequent results, as being controlled there will be less glucose attached to our corpuscle's (thanks Hana). Should I ignore my first test as a benchmark for my BG numbers?
 
I look at my first test, my diagnostic test, as a reflection of the diet I was on pre diagnosis, and my subsequent tests as a reflection of my diet and BG control in the period immediately prior to them. Does that answer your question, or am I still misunderstanding it?
 
it's rare that my BG hits 7mmol/l my 90 day results are based on 757 tests... The SD is 1.1 so little room for scary spikes... I have infrequent hypo's so they don't mask anything...

Unlike a T2 diabetic my insulin can't hide a spike that well, a T2 can be something like a 5 mmol/l before a meal, then 2 hours after be back at 5mmol/l but might hit a 11mmol/l spike at 1 hour mark, can't do that with injected insulin, unless your basal insulin is out and your quick acting teams up with the background to lower the blood glucose...

If my HbA1c came back a lot higher than my meter reading, I would be on a spike hunt...

Point is, because I test more often than a T2, and probably more than most T1's by looking at my meter and comparing that to my HbA1c result, I can see that looking at the 14 day result, isn't going to tell me any more information than looking at the 90 day result... So whether my 50% or 80% of the last several weeks make up most of my HbA1c result makes no difference as such..
 

Yes, that's it exactly. Thank you Sheepy.
 
Understand your point Jopar, but the converter on the main site isn't "naff". There is an equation which converts HbA1c to BG readings and vice-versa, and the site converter is based on that equation. The equation is
AVG BG = (HbA1c x 1.98) - 4.29
So if your HbA1c is 5.8 then your true average BG is NOT 6.1. Your meter may be accurate, and the average of your readings may be 6.1, but your overall average BG is not. Unless you do continuous monitoring, you of course don't know what your readings are in between tests no matter how often you test, but the equation above does apply to everyone within small tolerances.
Hope this helps
 
As a T2 MY 90 day average is based on around 650 readings. I test on average 7 times a day so before and at +2 hours for three meals plus a +4 hour before bed and the occasional +1 hour reading if I want to see if something new I've eaten is spiking SPECIFICALLY to rule out the 5, 11, 5 situation. As far as I would see a T2 would do the same as you do Jopar and check for spikes at one hour if they thought it necessary as most of do have the knowledge or intelligence to avoid a 5, 11, 5 situation in the first place.

The thing with spikes and HbA1c. We had a discussion about this a while back and I showed to Stephen it was quite possible for a T2 to be spikey AND maintain a very low HbA1c. The maths is pretty straightforward. I'll use an extreme example to show how.

Imagine person A who eats 6 small meals a day and has worked out what to eat so that their BG level is the same 2 hours after each meal. Let's say they always read a BG level of 6.0 after each meal. So for 120 days each of the 6 readings is always 6.0 and therefore there 120 day average is 6.0 and therefore the blood that is taken on day 120 that goes to get analysed has an average of 6.0 which means the person comes back with an HbA1c of 5.2%

Now imagine person B who also eats 6 small meals a day but for 5 of the 6 gets readings of 5.0 but for the 6 meal always eats something that spikes them to 11.0. Now their daily average is also 6.0 (5.0 x 5 plus 11.0 all divided by 6 is 6.0). Consequently if they do that for 120 days then their average is also 6.0 each day and on day 120 when the blood sample is taken it will have an average of 6.0 and their HbA1c will also come back as 5.2%

So person B is "hiding" a dangerous spike to 11.0 each day for 120 days while appearing to be as good as person A...

To me this is the primary reason why self testing is just as important as a quarterly HbA1c. The HbA1c would not pick up Person B's dangerous eating pattern.

Now I agree what I presented is simplistic and staged but you get the point and actually that point is backed up by research which shows people like Person A have slightly better outcomes than people like Person B even in cases where people like Person A end up with a sightly higher hBA1c than people like Person B.

As far as I know what is unclear from current research is if it's the spikes that lead to diabetic complications or having an average BG level over time that is too high that leads to them or some combination of both. I think Phoenix gave some links to so research at the time. I personally like to play it safe and believe it would be regular dangerous spikes that could cause me problems rather than the overall average and therefore I avoid spikes.
 

My HbA1c was done by a blood test from my GP so Jopar's point about a converter here is moot.
 
I think the key point Jopar, is that a blood plasma true average of 6.1 does NOT equate to an HbA1c of 5.8, and the site converter isn't naff. I'd hate you to think your overall average BG was lower than it really is. Do you know about the conversion of BG units to HbA1c units? I can give you some links tomorrow if it will help
 
Not sure if I explained that well. My concern is that you stated in your first post that "your meter is accurate because it's within 0.3% of your HbA1c", as if you thought they were the same "currency", whereas in fact the units are very different with plasma BG higher than A1c, increasingly so as numbers rise.
 
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