Prolonged blood sugar extremes — blood sugar that's either too high or too low for too long — may cause various conditions, all of which can lead to a diabetic coma.

  • Diabetic ketoacidosis. If your muscle cells become starved for energy, your body may respond by breaking down fat stores. This process forms toxic acids known as ketones. Left untreated, diabetic ketoacidosis can lead to a diabetic coma.

    Diabetic ketoacidosis is most common in people who have type 1 diabetes, but it can also affect people who have type 2 diabetes or gestational diabetes.

  • Diabetic hyperosmolar syndrome. If your blood sugar level tops 600 milligrams per deciliter (mg/dL), or 33.3 millimoles per liter (mmol/L), the condition is known as diabetic hyperosmolar syndrome.

    When your blood sugar gets this high, your blood becomes thick and syrupy. The excess sugar passes from your blood into your urine, which triggers a filtering process that draws tremendous amounts of fluid from your body.

    Left untreated, diabetic hyperosmolar syndrome can cause life-threatening dehydration and coma. Diabetic hyperosmolar syndrome is most common in middle-aged and older adults who have type 2 diabetes.

  • Hypoglycemia. Your brain needs glucose to function. In severe cases, low blood sugar may cause you to pass out. Hypoglycemia can be caused by too much insulin or too little food. Exercising too vigorously or drinking too much alcohol can have the same effect.

    Symptoms are influenced by the severity of the hypoglycemia. With longstanding diabetes, however, you may lose the early warning signs — such as hunger and perspiration — and may only develop symptoms when your blood sugar is dangerously low. This is called hypoglycemia unawareness.

Jun. 19, 2012