The levels up to 100 are considered normal, Most people who have had a blood glucose level over 300mg are considered to be into uncontrolled diabetis. When blood glucose level gets over 300mg, generally, the cause is uncontrolled diabetes. The effects of having a consistent high blood glucose can be devastating on the body which can cause complications such as heart disease and stroke, blindness, hypertension, diabetic neuropathy, nerve damage, depression, complications with feet, kidney disease and limb amputation.