In a nondiabetic person, a normal blood sugar level after fasting for eight hours is between 70 and 100 milligrams per deciliter (mg/dL), according to MedlinePlus. A higher blood sugar level can indicate that the person has prediabetes or diabetes.
A blood sugar level of between 100 and 125 mg/dL after fasting for eight hours means that a person has a type of prediabetes known as impaired fasting glucose and has an increased risk of developing type 2 diabetes, states MedlinePlus. If the result of a blood sugar test following an eight-hour fast is 126 mg/dL or higher, then that usually means that the person has diabetes.
Before a fasting blood test, the patient is asked to avoid eating anything for at least eight hours. This type of test should not be confused with a random blood glucose test, which can be taken at any time of day and does not require the patient to fast beforehand. In a random blood glucose test, a blood sugar level of 200 mg/dL or higher often means that the patient has diabetes, says MedlinePlus. However, a health care provider usually orders a fasting blood glucose test to confirm the diagnosis or rule out other possible conditions.