How dangerous are blood sugar levels above 300?

Fasting blood sugar levels above 300 are dangerous and require immediate medical attention. The normal range is from 90 to 160; dietary adjustments and sufficient exercise are the most effective ways to bring them lower, reports the University of Washington.

Blood sugar levels ranging from 160 to 240 are considered 'too high,' while those from 240 to 300 are considered very high and indicate the diabetes to be 'out of control.' Keeping blood sugar levels close to normal reduces the risk of developing serious, even life-threatening, complications; uncontrolled diabetes can lead to kidney damage, blindness, nerve damage and other serious conditions.