Ask the doctor: What's the difference between blood sugar and hemoglobin A1c?

Q. In your article on blood sugar control, you kept talking about hemoglobin A1c. I measure my blood sugar all the time, but my meter doesn't have a setting for a percentage reading. Is there a simple connection between blood sugar and hemoglobin A1c?

A. Blood sugar and hemoglobin A1c are connected, but they are different, too. Your blood sugar meter measures the concentration of glucose in the bloodstream at the instant you prick your finger. The reading is in milligrams of glucose per deciliter (a tenth of a liter) of blood, abbreviated as mg/dL. Blood sugar levels vary throughout the day. In people with diabetes, they can range from below 70 mg/dL to well above 200 mg/dL.