Without diabetes, your blood sugar should stay within the range of 70 to 120 milligrams per deciliter. But if you are diagnosed with diabetes, a more normal range for you may be between 80 and 180 milligrams per deciliter, according to the Juvenile Diabetes Research Foundation. Clearly, anything outside of this range is dangerous for a diabetic, and when it gets to a certain level, you may require immediate medical attention.
Anytime blood sugar is more than 240 milligrams per deciliter, it's a cause for concern among diabetics. It is particularly dangerous if your sugar is this high before a meal, since consuming any food would probably cause it to rise even more. When your blood glucose is above 240 milligrams per deciliter, it means your system isn't getting the energy it needs from glucose and could start breaking down fats. Your body starts producing ketones, which stem from fat deconstruction, possibly putting you into ketoacidosis that could lead to a diabetic coma. If your blood sugar surges to over 300 milligrams per deciliter, contact your physician immediately, since it could be life-threatening.