C. Ronald Kahn, M.D. President and Director, Joslin Diabetes Center What is the A1c blood test? The hemoglobin A1C test is a measure of what we call long term glucose control. The way this works ...

Sugar from food enters your bloodstream and attaches to your red blood cells, specifically to a protein called hemoglobin. A doctor may test your A1C level if you have or are at risk of developing ...