The A1c is an *average*. Statistically, averages are interesting animals, because an extreme score can pull an average in one direction or another. For example, let's say Patient A had BG that was 100, 100, and 100. That would yield an average of 100. (100+100+100=300, 300/3= 100.) Let's say Patient B had BG that was 45, 55, and 200. That would yield the same average. (45+55+200=300, 300/3=100).
Of course, the average is built somewhat differently, but basically, over a period of three months, if their blood glucose followed a pattern something like this, Patients A & B would have the same A1c. Patient B might think he was doing great, but Patient B has blood glucose that is wildly out of control. He is getting lows that statistically counteract the highs, but he's not in good shape. It's not good for him to be going hypo, to have these spikes, and to have such swings. But the A1c won't reveal that.
So if you are getting 150s after eating, but dropping back to 70, you can end up with an A1c around 5, which correlates with blood sugar averaging 101.
THis is information that I gleaned from a diabetic board and the same question.
Makes sense to me now.
Although, ac, I understand why one should be concerned with an A1c of 4.9 and a patient that takes meds...
I was curious as to why the A1c COULD be so low if a person was diagnosed with diabetes through fasting blood sugars.
Thanks for all your info though everyone!