A1c Curveball

[natayo]

Hi everyone, here comes a long post.

I just got my latest labs back with generally good results. But my latest A1c was 5.8, essentially unchanged from last time when it was 5.7. They also measured glucose level and got 90. Following everyone's good advice, I took my meter along and got an 88, so I have a fair amount of confidence that my meter is accurate.

The curveball in all this is that I think my average glucose justifies an A1c in the lower 5's rather than the upper 5's.

Once a week, I'll do what I call an 'all day test' where I test before and 1, 2, and 3 hours after meals. So I'll get a dozen or so readings through the day. Then I'll estimate my sugars for times I didn't test. For instance, I assume my morning fasting number applies from midnight to 8 am. And my bedtime number works from ten to midnight. When I do this, I get an average sugar around 105. Even if I assume a 10% error, I'm still only at 115 for an average. These numbers would seem to justify a lower A1c.

I've done a little research. First, in the August 2008 Diabetes Care, the lead article is on a new correlation for mean bs and A1c, using data from continuous monitoring. Even with this much data, they show a range of mean sugars for a given A1c. In fact, the 95% confidence interval for an A1c of 6 is a mean sugar range from 100 to 152, with the average being 126. (Note, based on this article, an A1c of 6 no longer corresponds to 135, but to 126!)

So this range of values includes testing errors, experimental method errors, and of course, the variation in how one persons body glycates sugar compared to how someone else does.

This person to person variation leads to the theory that some people are 'high glycaters' and others are 'low glycaters'. You and I can have the same average sugar and come up with somewhat different A1c. (Note: I also found a study that suggest the standard deviation of your sugar (the spikes) probably do not have an impact on A1c.

So my plan of action is this.

First, I've already sent in a home A1c test. Results should be back next week. If this test shows an A1c in the low 5's, then I'm done. If the home test agrees with my labs, then I'll move on to the second step.

The second step is to do more all day testing. Like maybe do a couple of days of testing every hour. Since my meter seems to agree with the lab, this should give me a more accurate measure of average sugar.

Then if my more refined value for mean sugar still justifies a lower A1c, then I'll know I'm probably a 'high glycater'.

The bottom line is that I know that spikes and average sugar drive the complications, not A1c. A1c is just the best measure they have found for watching your control.

So what are your experiences and thoughts?

[cherokee_psh]

An A1c of 5.anything is awesome. Sorry you are disappointed. It just means there maybe time when you are not testing the your bg is a little higher. You're still pulling a near normal A1C.

[Brian J]

My A1c's have ranged from 5.1 to 5.3 over the last few years and have been fairly consistent. This means my average blood glucose according to the new conversion has been in the 100 to 105 range. My meter averages are usually in the low 90's. I test a minimum of 8 times per day and probably average 10 tests/day. So according to my meter, I should have an A1c of 4.8 to 4.9. I think what really skews the A1c is the length of time a person is over 120. In people with normal glucose, the average person only spikes above 120 for a total of about 60 minutes per day and it usually occurs 45 minutes after eating. Most of them also had flat readings of 80 to 85 all during the night. I got these numbers from the following lecture: www.diabetes-symposium.org (http://www.diabetes-symposium.org)(turn on your speaker to hear the slideshow)
The 24 normal people in the study had A1c's from 4.3 to 5.4.

[Brian J]

Sorry, the link I wanted to use is :[url=http://www.diabetes-symposium.org/index.php?menu=authors]

Christiansen, Prof. J. S., On the occasion of the Annual Meeting of the EASD, Copenhagen, 13-Sep-06

What is Normal Glucose? – Continuous Glucose Monitoring Data from Healthy Subjects

[fgummett]

Does your all-day testing include overnight? Can we assume that someone with D has a flat BG level through the night... I know I don't :)

I always maintain that the A1C is useful but it needs to be taken in context of your own BG testing.

All that aside... your averages and A1c are really very good!

[shiftzor]

Don't forget you are checking a single point in time, your bg could be all over the place between your tests. Even if you test 10 times a day (like me). My bgs averages are always lower than my A1c I put it down to meal spikes, correction spikes, overnight unchecked hypos/hypers etc. Sadly the only better tool available is CGM which test every 1minute or so. You still can't get a perfect picture as the body is a complex beast different sites will give you different readings and lets not forget about the time between those minutes? Meters can only track trends over long periods and CGM can track trends for short periods (although newer cgms last up to a week) but neither is 100% accurate. You should be happy, we can all always do better but if you don't recognise you are doing well then you will never be happy.

[xMenace]

Does your all-day testing include overnight? Can we assume that someone with D has a flat BG level through the night... I know I don't :)

I always maintain that the A1C is useful but it needs to be taken in context of your own BG testing.

All that aside... your averages and A1c are really very good!

Overnight is my suspect. Try waking up and testing every hour (over many nights).

[Subby]

I'd put A1c to the side for the moment. I'd test more regularly on more days (and nights), work further on reducing fluctuation or SD (for which A1c is relatively bind) look into CGMS (even borrowing from a clinic may be possible) which could be a huge boon for you.

More regular testing and CGMS really will inform you better about whether you can relax, or what areas you need to work on if you do want improvement.

Then, work on the improvement.

Then, see what your A1c is doing down the track.

[pattywmom]

Keep in mind that A1c is testing Venous blood. Blood sugar testing is testing capillary blood and frankly the venous is what's going to affect our organs etc. Also, a 10-15% variance is 'acceptable' on most meters - you'd have to look at all that fine print. I have CGMS system and the things you DON'T know are pretty amazing! It's shocking how many little spikes and dips occur over the course of a day and especially overnight. Having a test every 5 minutes is nothing like point in time testing. Unfortunately overnight testing (waking up) isn't anything like reality because then you're not truly sleeping. CGMS is the only way I know of to get a good picture of overnight. Looking at my overnight I often wondered if I sleep-eat because of such severe spikes. It's also useful to see what stress does ... Amazing! Good Luck!