For most people, a fasting plasma glucose test is optimal. This blood test is usually done at a health care professional's office or in a lab in the morning after an overnight fast and before you've eaten. The normal, nondiabetic range for blood glucose is from 70 to 100 mg/dL. A level over 126 mg/dL usually means diabetes (except for newborns and some pregnant women). A fasting plasma glucose test of 100 mg/dL or greater, but less than 126 mg/dL, indicates impaired fasting glucose or prediabetes, a frequent precursor to diabetes.