Daily results vs Hbac1

[grufflybear]

I am recently dignosed T2 and I am testing myself regularly to see how well I can control with selected diet and weight loss. So far the results are pretty good, I test when I wake and before and then 2 hours after meals. Occasionally they are a little high (usually early mrning before breakfast) but still within the NICE guidelines and usually better. So... I have an Hbac1 test scheduled for September my question is this... if my daily testing remains within the present pretty good levels will my Hbac1 reflect these levels, by September I will have been on my diet regime for some 4 months so am I way off if I think that is heading for a good HBac1, or is there some "googly" that gets in the works like some horrendous spike which my testing regime has not detected ? I do my after meal test 2hours from the time I begin eating it....

 

[everydayupsanddowns]

Hi Gruffly

I guess the answer is 'probably yes'.

HbA1c (Glycated/Glycosylated Haemoglobin) is a test to measure how much sugary stickiness has stuck to your red blood cells.

Wikipedia:

Normal levels of glucose produce a normal amount of glycated hemoglobin. As the average amount of plasma glucose increases, the fraction of glycated hemoglobin increases in a predictable way. This serves as a marker for average blood glucose levels over the previous months prior to the measurement.

Since red blood cells last around 120 days it gives a reasonable indication of control over the last 3 months or so.

Since you are testing before and after meals you should be getting a 'fairly' good idea of the ebb and flow of BG. By testing at 2 hours you may be missing the peak of BG following meals, lack of phase 1 insulin can mean that T2s get a higher spike around 1 hour, but everyone is different, as are different meals).

If your spot BG tests are giving you a decent spread (and you are not missing long periods of high BG) then there are ready reckoner conversions which can predict your likely A1c.

The one I use is:
Predicted HbA1c = (Avg BG+2.52)/1.583

I've not had an A1c since I found that, so I don't know how accurate it is for me, but I've read others saying it gave a pretty good indication

 

[Mark T]

The answer as I understand it is that your testing is only a snapshot, so there is a risk that it might not capture all.

The thing that caught me out was that my daytime levels looked good but I hadn?t realised that I was running a tad higher overnight.

 

[Robster65]

Hi Gruffly.

As Mike says, it reflects your average over the previous few weeks but is 'weighted' towards the more recent past. I think it's something like 50% towards the past 3 or 4 weeks and tapering off towards a couple of moths or so.

So, what you test now will have little effect on your result but the few weeks before the test will be what's reflected. I, like Mike, test soemthing like 5-8 times a day, maybe more, which gives a fairly good indication of the spread on a weekly average basis. I use a piece of software for recording BGs which uses a similar algorithm and has been within +/- 0.2 of the past 2 or 3 HbA1cs, so it is a fairly good reckoner providing you're hitting some of your spikes and lows. If they form a minimal part of your daily BG, then you'll be fine to use that algorithm.

As Mark says, the nighttime ones form a large part of the 24hr cycle and often go untested, but if your waking and bedtime BGs are fine, you're likely to stay fairly level unless you eat carbs late and they cause a late spike which subsides by morning.

Stick at it and try to vary your times to see where the spikes occurr. You may be surprised.🙂

Rob

 

[HelenM]

The formula works well (+/- 15%) for most people who test a lot ie before and after meals, fasting and sometimes at night. It is derived from a fairly recent study that involved people in several countries.

However there are still quite a lot of people who aren't average!.

• The formula may not be true for all ethnic groups. ( eg there were very few people of Asian origin in the study )
• Some peoples red blood cells don't live as long, which can alter the result.
• Some people (with forms of anaemia) don't have as many red cells as others so their HbA1c results will be lower than they should be.
• Lastly there are some people that for some unknown reason seem to glycate very much more or very much less than others.
  A high glycator will have a higher HbA1c than a 'normal' glycator with the same average glucose levels and vice versa for low glycator.

 

[everydayupsanddowns]

Good points Helen, thanks.

Backs up why A1c targets should be agreed with your care team who (should) know your history/case details rather than just going by general guidelines.

M

 

[Robster65]

Very interesting. Though I would have my doubts that any of those factors (other than maybe ethicity) would be known or taken into account by most teams.

I would guess problems such as sickle cell anaemia would have an effect, which is obviously a specific ethnic problem. Fortunately, I seem to be average. Story of my life ! 🙄

Rob

 

[grufflybear]

Thank you for replies, perhaps I should set the alarm clock to check how I am during the night once in a while, all very interesting information...

 

[mcdonagh47]

better. So... I have an Hbac1 test scheduled for September my question is this... if my daily testing remains within the present pretty good levels will my Hbac1 reflect these levels, by September

Good numbers over the couple of months beforehand should be reflected in a good HbA1c.

But don't forget .. the HbA1c is NOT a measure of average BGs ... they both measure different things.

 

[Robster65]

One positive about diabetes is that it does encourage a person to find out how the body functions and what can go wrong if we don't look after ourselves.

I believe that being well-informed is a key to taking better overall care of ourselves.🙂

Now, where's that cheesecake ? 🙄

Rob

 

[FM001]

I personally use my meter averages as a truer guide to my diabetes control than a hba1c test.

 

[Robster65]

It would depend on how many tests you do and when you do them.

If (hypothetically) you were to test 10 times a day and got results below 7 every time, your average would be excellent. But if you were missing spikes up to 15 or were high all night, your Hb would reflect that in a poor result.

Consequently, the HbA1c shouldn't be dismissed unless you're sure that your testing regime shows a true average, and corresponds with your Hb.🙂

Rob

 

[grufflybear]

Thank you, that makes sense - I will check during the night as that is the great unknown for me at the moment