A blood glucose test measures the amount of sugar in a sample of blood, states MedlinePlus. From the test, experts have created a blood-glucose level scale that tells doctors whether an individual has normal, high or low blood-sugar levels.
Normal blood-sugar levels vary in a single person throughout the day. A fasting blood-glucose level between 70 and 100 milligrams per deciliter is considered normal, states MedlinePlus. A fasting level of 100 to 125 mg/dL means one has impaired fasting glucose, which is a type of pre-diabetes. A level of 126 mg/dL and higher usually means one has diabetes.
WebMD provides target blood-sugar levels for diabetics over the age of 20. The recommended fasting level should be less than 100 mg/dL, and 1 to 2 hours after a meal, it should be less than 180 mg/dL. At bedtime, the level should fall between 100 and 140 mg/dL and before a meal from 70 to 130 mg/dL. Individuals with diabetes can test their own blood-glucose levels at home by purchasing a kit with a finger-prick device that draws a drop of blood. The blood is then placed on a strip or into a machine that reads how much sugar/glucose is the blood.