In type 1 diabetes, it is normal for glucose levels go up and down slightly throughout the day. Even in someone without diabetes, the blood sugar may rise after a meal (120 to 140 mg/dl) and then return to normal (70 to 100 mg/dl) in a few hours. In diabetics, blood sugar levels usually remain above 160 mg/dl.

In diabetics, the blood sugar level is measured at certain times of the day: before meals, after meals, at bedtime, or after a dose of insulin. A random blood glucose level is a measurement of blood glucose that is performed any time, without regard to meal times, insulin doses, or time of day.