The HbA1c level indicates your average blood sugar levels over the past 2–3 months. The HbA1c or A1C test measures the amount of blood sugar or glucose that's bound to your red blood cells. If your body can't use glucose as it should, more of it sticks to the blood cells and builds up. Doctors use the test results to diagnose and monitor prediabetes and diabetes. The results are reported as a percentage, and normal levels are less than 5.7t.