If the body produces too much pituitary hormone or too little insulin, the amount of sugar in the blood rises abnormally, producing a condition known as hyperglycemia. In hyperglycemia the blood may contain as much as four times the normal amount of sugar. Hyperglycemia in itself is not lethal, but it is a symptom of a serious disease, diabetes mellitus. Diabetes is sometimes caused by a tumor or other condition in the pancreas that prevents the formation of insulin. Diabetic patients do not die of hyperglycemia, but if they are not given injections of insulin they may die from such causes as the accumulation of poisons in the body, produced by altered metabolism of fats; the body of the diabetic consumes fats as a substitute for the sugar that it cannot use.
If an excessive amount of insulin is injected into the body, the amount of sugar is reduced to a dangerously low level, a condition known as hypoglycemia or insulin shock. Controlled insulin shock is sometimes used in the treatment of certain types of mental illness.
In a normal individual, if the amount of sugar in the blood rises abnormally, the excess is removed from the blood by the kidneys and excreted in the urine. The presence of sugar in the urine is called glycosuria, and although it is an important symptom of diabetes, it is not always found in diabetic patients; moreover, glycosuria may appear in normal individuals immediately after a large meal. The critical test for diabetes is neither hyperglycemia nor glycosuria, but blood-sugar tolerance: after ingesting sugar, both normal and diabetic individuals show an increased percentage of blood sugar; the percentage remains high in the diabetic, whereas in the normal individual the excess glucose is rapidly converted into glycogen.