Glucose, fasting blood: A method for learning how much glucose (sugar) there is in a blood sample taken after an overnight fast. The fasting blood glucose test is commonly used in the detection of diabetes mellitus. A blood sample is taken in a lab, doctor's office, or hospital. The test is done in the morning before the person has eaten. The normal, nondiabetic range for blood glucose is from 70 to 110 mg/dl, depending on the type of blood being tested. If the level is over 140 mg/dl, it usually means the person has diabetes (except for newborns and some pregnant women).