How do Fasting Readings Correlate to A1c

[crashtestdummy]

This may not be a valid question because there may be too many other factors involved.

If fasting numbers are lets say averaging at 105 then that gives and a1c number of 5.3. Can you get a good idea of what your A1c is from averaging your fasting testing numbers.

I have no idea if this makes any sense. Maybe someone out there knows what I am asking.

[Subby]

They don't, because fasting numbers are of course only indicating your BG control for part of the time.

Some find that average BG meter results (this would be including pre and post meals as well) give a reasonable indication of A1c. Some insist on that, though I think there are too many variables still to be able to apply this idea blindly. You could try comparing your tester averages with your A1c the next few times, you might get a feel for the correlation.

[fgummett]

It depends... :)

If your Fasting BGs are indicative of your average BG throughout the rest of the day (and night) then there should be a strong correlation to your A1c... but that is unlikely ;)

Remember that the A1c is effectively an average (mean) of all your BG levels over the last 90 days or so... weighted towards the last 30 days or so.

So it makes sense that the more BG test you do every day (and night) will give a closer average to the A1c.

I recall reading that the post meal (postprandial) numbers seemd to have a greater bearing on A1cs.

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Canadian Diabetes Association 2008 Clinical Practice Guidelines... (http://www.diabetes.ca/files/cpg2008/cpg-2008.pdf#page=46)The results of multiple tests each day provide information that is better correlated to A1C than fasting results alone. BG measurements taken after lunch, after supper and at bedtime have demonstrated the highest correlation to A1C.

[ShottleBop]

According to this study (found at find-health-articles.com) [Note that this study was conducted in Japan, but I have seen other reports of studies that say that the two-hour postprandial is a better indicator of HbA1c than the fasting glucose measurement]:

Contribution of fasting and postprandial hyperglycemia to hemoglobin A1c in insulin-treated Japanese diabetic patients.

Full Abstract

The contribution of fasting and postprandial glucose to hemoglobin A(1c) (HbA(1c)) levels was evaluated in insulin-treated patients. In 57 insulin-treated, diabetic out-patients, fasting glucose (before breakfast (B-FG), lunch (L-FG) and dinner (D-FG)) and postprandial glucose (B-PPG, L-PPG and D-PPG) levels were determined by the patients themselves at home using glucose self-monitoring apparatus over the course of one week. The correlation between HbA(1c) levels and self monitored blood glucose levels were calculated. In the conventionally treated group, there was a significant correlation between HbA(1c) and fasting glucose (FG) levels only before lunch, but at 2 hr after (PPG) all meals. In the intensively treated group, a significant correlation between HbA(1c) levels and FG levels was found before lunch and at 2 hr after breakfast and dinner. In all subjects, only FG levels before lunch correlated significantly with HbA(1c) levels, although PPG levels were significantly correlated with HbA(1c) at all points. The correlation was highest with PPG after breakfast and dinner. The sum of all FG, PPG and FG + PPG levels was significantly correlated with HbA(1c) levels. Postprandial hyperglycemia after breakfast and dinner should be regarded as most important for improving HbA(1c) levels in insulin treated diabetic patients

[JayDee1950]

Copied from the ADA website:

How does the A1C test look backward?
Suppose your blood sugar was high last week. What happened? More glucose hooked up (glycated) with your hemoglobin. This week, your blood glucose is back under control. Still, your red blood cells carry the "memory" of last week's high blood glucose in the form of more A1C.

This record changes as old red blood cells in your body die and new red blood cells (with fresh hemoglobin) replace them. The amount of A1C in your blood reflects blood sugar control for the past 120 days, or the lifespan of a red blood cell.

Full article:
A1C - American Diabetes Association (http://www.diabetes.org/living-with-diabetes/treatment-and-care/blood-glucose-control/a1c/a1c.html)