Glucose levels vary before and after meals, and at various times of day; the definition of "normal" varies among medical professionals. In general, the normal range for most people (fasting adults) is about 4 to 6 mmol/l or 80 to 110 mg/dl. (where 4 mmol/l or 80 mg/dl is "optimal".) A subject with a consistent range above 7 mmol/l or 126 mg/dl is generally held to have hyperglycemia, whereas a consistent range below 4 mmol/l or 70 mg/dl is considered hypoglycemic . In fasting adults, blood plasma glucose should not exceed 7 mmol/l or 126 mg/dL. Sustained higher levels of blood sugar cause damage to the blood vessels and to the organs they supply, leading to the complications of diabetes. 
Most recently, the largest randomized control trial to date (with 6104 enrolled patients) comparing the effects of intensive glucose control vs. conventional glucose control in ICU patients found that tight glucose control significantly increased mortality at 90 days after admission to the ICU as compared to conventional glucose control (% increase in the absolute risk of death).  In this trial (the NICE-SUGAR Study), patients randomised to the intensive glucose control group had a target blood sugar range of to mmol/L while those placed in the conventional glucose control group had a blood glucose target range of to mmol/L (as compared to to mmol/L in Van den Berghe, 2001). Patients were enrolled from mixed ICU wards (as compared to a surgical ICU in Van den Berghe, 2001). The NICE-SUGAR trial may very well change our approach to the management of stress-induced hyperglycemia in the ICU.