A hemoglobin A1c (HbA1c) test measures the amount of blood sugar (glucose) attached to

hemoglobin. Hemoglobin is the part of your red blood cells that carries oxygen from your

lungs to the rest of your body. An HbA1c test shows what the average amount of glucose

attached to hemoglobin has been over the past three months. It's a three-month average

because that's typically how long a red blood cell lives.