Patients do not need to fast before an A1C blood test, which is considered a significant advantage over traditional blood glucose testing, notes WebMD. The A1C test also measures and averages blood sugar levels over months, which may help identify patients who have diabetes but are not aware.
The A1C test measures the amount of glycated hemoglobin in the blood. If the patient has more glucose in his blood, it causes the A1C percentage to be higher. Patients with an A1C rating of 5.6 to 6.4 are considered to be prediabetic, while patients with an A1C rating over 6.5 are considered to have diabetes.