Diabetic ketoacidosis
DKA happens when a person does not have enough insulin in their body.  All of the cells in the body need glucose (sugar) to survive, because the body needs sugar to make energy.  Insulin breaks down glucose into a form that the body can use for energy.  Without insulin, sugar stays in the blood and cannot get into the cells.  This causes high blood sugar levels and makes it impossible for the cells to use glucose to make energy.