HbA1c is measured as a percentage and provides an overview of your average blood glucose control for the past few months. Hemoglobin, the protein found in your red blood cells, carries oxygen from the lungs to all the cells of the body. It also links up with sugars such as glucose (glycation) as they enter your red blood cells. The more glucose in your blood, the more hemoglobin gets glycated. As your red blood cells die and get replenished every three months, HbA1c gives the measure of your blood sugar over that time.