The normal 'fasting' plasma glucose level for adults of all ages is less than 100 milligrams per deciliter, according to the American Diabetes Association. Levels ranging from 100 to 125 mg/dl indicate prediabetes; individuals testing 126 mg/dL or higher are diagnosed as diabetic.
Fasting blood glucose tests are typically performed in the morning, when an individual has had nothing to eat or drink -except for water- for a full eight hours prior to administration.
Other methods used to check for abnormal blood glucose levels include the Hemoglobin A1c Test -which measures levels over a period of two to three months- and the oral glucose tolerance test -taken before and after consuming a sweet drink to monitor how the body processes glucose.
