Q: If the sugar level crosses the normal range does it prove that the person has diabetes or it may be due to any other reasons, like excess intake of sugar, depression, indigestion etc.

A:If the blood (plasma) glucose level is greater than 140 mg/dl (fasting) and 200mg/dl (2hrs after 75 gm glucose) then the person is definitely diabetic. Occasionally, these values may occur during major illness in someone not known to be a diabetic, and normalise after recovery. But such patients do remain prone to diabetes in the future too.