Blood sugar for diabetics reaches dangerous levels when patients are unable to treat themselves or when blood glucose levels go above 160 milligrams per deciliter or below 70 milligrams per deciliter. Hypoglycemia, which results from low levels of blood glucose, is not fatal by itself but can lead to accidents when patients fall down stairs or swerve into oncoming traffic, states the Joslin Diabetes Center.
People without diabetes have plasma blood glucose levels that typically run under 100 milligrams per deciliter, according to the Joslin Diabetes Center. Blood glucose levels in a diabetes patient become dangerously high when they exceed the individual blood glucose target of the patient or go above 160 milligrams per deciliter and cause hyperglycemia. If these levels run for long periods, the patient increases the risk of developing complications such as stroke, kidney disease and heart attacks. Short-term health problems can also develop if blood glucose levels run above 180 milligrams per deciliter for three or more consecutive days.
Blood glucose levels become dangerously low when they run below 70 milligrams per deciliter and, subsequently, cause hypoglycemia. Patients with low levels of blood glucose are usually sweaty and shaky and may experience seizures and bouts of unconsciousness, explains the Joslin Diabetes Center. Patients can reduce the risk of hypoglycemia by recognizing individual symptoms and carrying carbohydrate foods for treatment.