What Are Critical Ranges for Glucose?

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In medicine, laboratory results--including glucose readings--that indicate a life-threatening situation for a patient are known as "critical"or "panic" values and must be reported immediately to either the attending physician or the appropriate health care professional. Critical glucose levels are no exception.


Glucose, a simple sugar resulting from the breakdown of carbohydrates in the diet, is the main source of energy in most living organisms. Like any other body chemistry, it is assigned a normal value range.

Normal Glucose Values

Normal values must be established before critical glucose ranges can be recognized. Normal reference values are established through clinical studies and testing, and describe the results expected to be found in apparently healthy individuals. A normal 8- to 10-hour fasting glucose in a healthy adult should fall between 70 to 110 mg/dL.

Critical Glucose Levels

Critical glucose levels fall into two categories: critical low levels and critical high levels. Glucose levels that fall into a critical range may trigger irreversible damage to the body or even death.

Critical Low Glucose: Hypoglycemia

Hypoglycemia refers to abnormally low glucose levels. Glucose levels below 50 mg/dL are considered hypoglycemic, and a glucose of 40 mg/dL is a "critical value" requiring immediate action. Symptoms of critically low glucose include fainting, weakness, confusion and unconsciousness if not treated.

Critical High Glucose: Hyperglycemia

Hyperglycemia refers to abnormally high glucose levels. The American Diabetic Association recommends that a fasting glucose level above 126 mg/dL be considered hyperglycemic. Glucose levels in the 400 to 450 mg/dL range are considered "critical values" and require immediate attention. Symptoms of critically high glucose include confusion, lethargy, thirst, weak pulse and nausea. Diabetic coma and death may follow if not treated immediately to reduce the level.


It is up to each laboratory to establish its own set of critical glucose ranges which require immediate physician notification. Reference ranges may vary based on methodology and the instrumentation involved.