Hemoglobin A1C is a historical number showing your blood sugar levels over the past 60-90 days.
So if your A1C is high enough to be put on metformin, you need at least 75 days to get a number that's "stable" and shows a reduction to the A1C that got you pegged as Diabetic.
Below 7.0, you're tagged DM2 but showing adequate control. 7.0-7.9% you'll be issued with a counseling of get it in control. 8.0%-9.0% is issuable, but with major reluctance and a stern warning to get healthy and like, now!
The required doctor status letter items are
- Statement you are being treated for DM2 and your recent A1C number backed up by the blood lab report
- What medication are you taking, what dosage, what frequency, and are there any side effects.
- Examination and report Any problems with nervous system, especially peripheral nerves
- Examination and report Any problems with cardiac system
- Examination and report Any problems with eyes and retina
- Examination and report Any problems with kidneys
If your A1C is above 6.5%, this will be a special issuance. AME of the quality like Dr. Bruce Chien can minimize the deferral time by making sure the submission is done properly.
If your A1C is below 6.5%, you can qualify for the CACI Pre-Diabetes issuance. This means, the AME can issue you in office, but this is your "yellow card" to stay at that level and not let it get to 6.5% or higher.
Getting your blood sugar under control is imperative. It very much is an "But I feel fine" killer disease. I know of an acquaintance under 40 with 3 kids that still has not come to grips and proper control, even after first losing 2 toes, then his lower leg (gangrene from the toes), and 2 major cardiac events, and now in stage 2 kidney failure.
Blood sugar monitors are inexpensive. Getting one and then using the guidelines from the American Diabetes Association will help.
Walmart makes a home A1C test under their "ReliOn" brand. This is the same item that was being sold under the Bayer brand. They cannot be used to report to the FAA, but for a home test are reasonably accurate. The official lab result was within 0.2% of the home test. I use these for "in between doctor visit" monitoring.
Like Murphey said, working with a top level, very experienced AME such as Dr. Bruce Chien is optimal. Just don't get connected with a "take your $80-120 and defer everything" AME.