Hyperglycemia and Hypoglycemia

What is hyperglycemia?
Hyperglycemia (hi"per-gli-SE'me-ah) is an increase in plasma glucose (blood sugar). It can turn into a complex medical condition -- diabetic ketoacidosis (ke"to-as"id-O'sis) and coma -- if it's not treated on time and adequately. Hyperglycemia is usually the first sign of diabetes mellitus. Symptoms of hyperglycemia are

polyuria (pol"e-YUR'e-ah) (excess urine)
polydipsia (pol"e-DIP'se-ah) (thirst)
polyphagia (pol"e-FA'je-ah) (excessive hunger)

What is hypoglycemia?

Hypoglycemia (hi"po-gli-SE'me-ah) is a low level of plasma glucose (blood sugar). It's a dangerous condition because glucose is the major source of energy for the brain. Lack of glucose, like lack of oxygen, produces brain damage or even death if the deficit is prolonged. Hypoglycemia can occur after insulin excess and/or inadequate glucose intake, among other causes. These situations are common in people with diabetes who receive too much insulin or who don't eat enough.

Hypoglycemia starts to cause these symptoms when glucose levels fall below 50 milligrams per deciliter (mg/dL):

sweating
tremors
anxiety
hunger
dizziness
headache
cloudy vision
confusion
abnormal behavior
convulsions
loss of consciousness

What should you do if hypoglycemia occurs?
If you're suspected of hypoglycemia, you must eat carbohydrates (starches or sugars) immediately.

Related AHA publications:

Diabetes, Heart Disease and Stroke (also in Spanish)

Related AHA Scientific Statements:
Diabetes Mellitus