Yes, typically your fasting levels are some of your lowest blood sugar levels and unless they are routinely over 150/8.3 mmols then they aren't even "in the danger zone" of causing potential longer term problems.

But what they do, do is form your lower end of your "range" (again typically - some will have lower after meal numbers then fasting numbers but that is very uncommon on a long term basis).

So it's primarily the "dietary sourced sugars" that we get from eating that end up as the real "excess" that gets stuck to our blood cells in the (quantity) that is reflected in our A1C.

It is a reasonable test for diagnostics in terms of "big picture", but the OGTT that you will do and/or combined with a 12 hour fasting test give your Doc far more detailed information so they can make better treatment decisions - both tests individually really dial in to the two different processes that combined form your A1C.

A couple of questions there and it sounds like you have guessed the answers pretty well.

First, yes, your last 30 days has a greater effect on your A1C then the earlier 60. It simply has to do with the rate that new blood cells are produced and how prolific they are in your blood stream.

A blood cell lives for (about) 90 days and A1C looks to see how much sugar is stuck to (them) to calculate your A1C. So while "some" that are tested will be up to 90 days old, most of them will be "somewhat less", so what happened with your sugar more recently is more likely to have the most effect.

Another point on that same line, Fasting Numbers have almost "zero effect" on our A1C numbers - even if they have been running a little bit high. They do effect our range/average which can push everything up, but A1C is "most effected" by our after meal sugars.

(and all of the above shows the "limitations" of A1C - it doesn't pin point "what" blood sugars might be an issue and doesn't really tell you whether things have got better or worse within that 3 month period itself - were you really high at month one and greatly improved or are things going down hill fast - need yet your "next" A1C before that is apparent)

The OGTT (Oral Glucose Tolerance Test) where you drink that 75G "shooter" and then they do the tests at one hour intervals (for 3 hours - at least that is was the method when I used to do the tests).

The (theory) is that they overload your system with carbs (and the liquid has a near instant uptake of the sugars - it's pure glucose so needs no digesting) and then the tests see how quickly your pancreas reacts and then how effective your insulin production is at whatever level of resistance you have.

Loading up on carbs (blowing your sugar levels up) for a couple of days "before the test" will just wake up your system to "what is coming".

Will a couple days of "out of range" effect your A1C? Minimally. If I did it one meal a day for say even 3 days in a row that would be about 12 hours worth of "out of range" (4 hour typical time to metabolize) in a 90 day period - even with the last month being the more influential, 12 hours out of the 720 total hours in the last month will get pretty much "averaged in"

My FBS are typically my highest of the day. They were running in the high 9's to 11's and even occasionally as high as 14+. Since I retired, I have really been focusing on getting increased activity every day and that has brought down the FBS #'s significantly. Speaking of activity...off to the treadmill I go🚶😊

I didn't know that about the fasting levels having no affect. Makes sense though, it's adding no sugar to stick to your cells.
Thank you!

Sorry, TOM, I don't have the answers, but I'm sure someone will have. Good luck on your results🍀.