Why Does A1c Measure Blood Sugar Over Time?

— -- Question: My name is Tom, I'm from Everett. I was diagnosed with type 2 diabetes in 1998. I've heard that the HA1c is a measurement of the average of blood sugar over a period of time. If this is true, why?

Answer: Hi Tom. Yes, the hemoglobin A1c is a measure of the average blood sugar over a three month period. And what this is, is that blood sugar attaches to the blood cells in your system and rides around with the blood cells in your system. And the higher your blood sugar, the more sugar that is attached to the red blood cells. And since the red blood cells live for three months and they turn over every three months, then every three months you have a new average from the hemoglobin A1c test to reflect your average blood sugar for that three month period.