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Permalink Reply by Zoe on March 8, 2011 at 5:20pm

There would be no way that an A1C could weight for types of blood sugars, only a time period. It is an average and has know idea what has caused a certain number. I know there is a formula that tells you how much is weighted for more recent numbers versus those further back. I'm assuming you have had highs in one or the other of those areas and wondered how badly they would slant your A1C. Think of it this way, you only test your fasting one time per day. But you test your postprandial three times a day (or more). So if the PP's are often or always high that means you are spiking at least three times a day. It also would depend on how long you spend at the higher numbers. It's the total time spent at a high range that influences the average, it doesn't matter when (or why) that high occurs.

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Permalink Reply by Donna H on March 8, 2011 at 5:26pm

Zoe is correct. One fact that I learned is that, although it is generally a 3 month average, the more recent bgs have greater impact on the overall result.

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Permalink Reply by acidrock23 on March 8, 2011 at 5:29pm

I would think fasting, if only because you eat 3-6-10-? times/ day but the rest of the time you are "fasting"? I think that it might be "both" though because if the postprandial #s aren't correct, they spill over/ mess up your fasting?

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Permalink Reply by Brian (bsc) on March 8, 2011 at 5:48pm

The answer to this lies in your particular fasting and postprandial responses. If your fasting is perfectly normal, but your postprandial spikes up over 200 mg/dl and then struggles to reach 140 mg/dl by two hours, then more than 50% of your A1c may be due to your postprandial blood sugars. On the other hand, if your fasting is elevated, but you follow a low carb diet and have almost no postprandial blood sugar rise, then your A1c will be mostly a reflection of your fasting number. If you believe you are one of these end cases, it makes sense to show your doctor your logs, so that he can properly understand what your A1c means.

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Permalink Reply by John on March 9, 2011 at 12:47pm

Depends on your A1c reading. High A1c -- post prandial, low A1c fasting

From http://www.fpnotebook.com/endo/lab/hmglbna1c.htm

Fasting vs post-prandial hyperglycemia
Hemoglobin A1C <7.3%:
Postprandial Glucose: 30%
Fasting Glucose: 70%
Hemoglobin A1C 7.3-8.4%
Postprandial Glucose: 50%
Fasting Glucose: 50%
Hemoglobin A1C 8.5-9.2%
Postprandial Glucose: 55%
Fasting Glucose: 45%
Hemoglobin A1C 9.3-10.2%
Postprandial Glucose: 60%
Fasting Glucose: 40%
Hemoglobin A1C >10.2%
Postprandial Glucose: 70%
Fasting Glucose: 30%

Note the oft-quoted comment that A1C is the three month average of blood glucose is wrong. The average is strongly biased to more recent readings.

From http://www.faqs.org/faqs/diabetes/faq/part2/section-11.html

...the HbA1c is an exponentially weighted average of blood glucose levels from the preceding 4 weeks, with the most recent 2 weeks being by far the most important.

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Permalink Reply by s6954118 on March 9, 2011 at 1:01pm

the three weeks before your test have more eieght than the last three weeks of the 3 month period

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