For adults without diabetes, the normal fasting blood glucose range is 70 to 100 milligrams per deciliter, says the National Institutes of Health. Adults diagnosed with diabetes should have a pre-meal blood sugar range of 70 to 130 milligrams per deciliter, according to the American Diabetes Association.
Fasting blood sugar is determined by testing blood when a person has not eaten for at least eight hours. A fasting blood sugar value less than 70 milligrams per deciliter indicates low blood sugar (hypoglycemia), says the American Diabetes Association. A result of 100 to 125 milligrams per deciliter indicates prediabetes, and a value 126 milligrams per deciliter or higher indicates diabetes, states the Mayo Clinic. The Mayo Clinic also notes that blood sugar can be affected by amount and type of food eaten, alcohol, exercise, some medications, stress, hormones and illness.