The A1C test gives you a picture of your average blood glucose (blood sugar) control for the past 2 to 3 months. The results give you a good idea of how well your diabetes treatment plan is working.
Hemoglobin, a protein that links up with sugars such as glucose, is found inside red blood cells. Its job is to carry oxygen from the lungs to all the cells of the body. Glucose enters your red blood cells and links up (or glycates) with molecules of hemoglobin.
The more glucose in your blood, the more hemoglobin gets glycated. By measuring the percentage of A1C in the blood, you get an overview of your average blood glucose control for the past few months.
The American Diabetes Association suggests an A1C of 7% or lower for non-pregnant adults who have diabetes.
Source: American Diabetes Association/Living With Diabetes