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What Are Critical Glucose Ranges?

author image Annie Summers
Annie Summers began writing educational materials in 1975. She covers medical topics for various websites and authors public health materials. Summers is registered and certified as a medical/surgical assistant and EKG technician. She is also licensed as a pharmacy technician.
What Are Critical Glucose Ranges?
Blood glucose can be monitored at home. Photo Credit: Wavebreakmedia Ltd/Wavebreak Media/Getty Images

Patients with diabetes try to keep their glucose levels in the normal range to prevent damage to internal organs and nerves, and to preserve their eyesight. They work with physicians as well as specialist nurses and dietitians to achieve this. Patients with type II diabetics, may have had symptoms of high blood glucose that led them to seek care, but often this type of diabetes is diagnosed by routine blood tests. With proper care, blood glucose levels may never reach a critical level. Type I diabetes, treated with insulin, is usually much more difficult to control, especially in adolescence. Type I diabetics are far more likely to have a critical glucose level at some time in their lives.

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Critical Low

Headache can be a symptom of hypoglycemia.
Headache can be a symptom of hypoglycemia.

Called hypoglycemia, this deficiency of glucose in the blood is considered critical at, or below, 40 milligrams of glucose per deciliter of blood, or 40 mg/dL. However, this figure must be adjusted individually, as the exact level at which an a person develops symptoms varies. Insulin and other diabetes medications can cause hypoglycemia under certain conditions. As an example, skipping a meal, but taking the usual dose of insulin can cause hypoglycemia. With Type II diabetes, medication errors and drug interactions can cause hypoglycemia. It is suggested that diabetics not drive with a level below 70. According to “Understanding Pathophysiology,” the initial symptoms of headache, weakness, pallor, intense hunger, shakiness and irritability can occur with levels of 45 to 60 mg/dL. This must be treated with an immediate replacement of glucose. Severe hypoglycemia can lead to seizures, coma and even death.

In the Middle

Some diabetics must check glucose levels before and after meals.
Some diabetics must check glucose levels before and after meals.

Blood glucose levels that are not in the critical range are not necessarily healthy ones. The American Diabetes Association has established ideal glucose levels: For non-diabetics, the range is 70 to 99 mg/dL fasting, and 70 to 140 mg/dL. For diabetics, the target levels are 70 to 130 mg/dL before meals and less than 180 mg/dL one to two hours after eating. Keeping the blood glucose within this range is the best protection against the complications of diabetes.

Critical High

Blurred vision can occur with hyperglycemia.
Blurred vision can occur with hyperglycemia.

Hyperglycemia is an excess of glucose in the blood. This is what causes the symptoms of diabetes. The critical level is 450 mg/dL and above. As the blood glucose increases above normal, the classic symptoms of increased thirst and frequent urination occur. Blurred vision and fatigue are also common symptoms of high blood glucose. If the glucose continues to rise, glucose appears in the urine. When critical levels are reached, a diabetic becomes dehydrated and begins to metabolize body fat instead of glucose, which is called diabetic ketoacidosis. An acetone smell on the breath may arise. At this point, hyperglycemia must be treated with insulin and supportive measures to prevent coma and possible death.

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