What Is The Normal Range For Blood Sugar Levels, And What Blood Sugar Level Constitutes A True Emergency?

Dr. Horton answers the question: 'Normal Range For Blood Sugar Levels?'

By
Edward S. Horton, M.D., Section Head, Clinical Research at Joslin Diabetes Center; Professor of Medicine, Harvard Medical School
August 14, 2008, 1:15 PM ET
2 min read

— -- Question:What is the normal range for blood sugar levels, and what blood sugar level constitutes a true emergency?

Answer:Now, in a normal individual we measure blood sugar under different circumstances. What we call fasting blood sugar or blood glucose levels is usually done six to eight hours after the last meal. So it's most commonly done before breakfast in the morning; and the normal range there is 70 to 100 milligrams per deciliter.

Now when you eat a meal, blood sugar generally rises and in a normal individual it usually does not get above a 135 to 140 milligrams per deciliter. So there is a fairly narrow range of blood sugar throughout the entire day.

Now in our diabetic patients we see both low blood sugar levels that we call hypoglycemia, or elevated blood sugars, hyperglycemia. Now, if the blood sugar drops below about 60 or 65 milligrams per deciliter, people will generally get symptoms, which are some shakiness, feeling of hunger, maybe a little racing of the heart and they will usually be trenchant or if they eat something, it goes away right away. But if blood sugar drops below 50 and can get down as low as 40 or 30 or even 20, then there is a progressive loss of mental function and eventually unconsciousness and seizures. And of course that is very dangerous and a medical emergency.

On the other side, if blood sugar gets up above 180 to 200, then it exceeds the capacity of the kidneys to reabsorb the glucose and we begin to spill glucose into the urine. And if it gets way up high, up in the 400s or even 500s, it can be associated with some alteration in mental function. And in this situation, if it persists for a long time, we can actually see mental changes as well. So either too low or very exceedingly high can cause changes in mental function.

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