Managing Diabetes: Ketone Testing What are Ketones? How do They Cause Diabetic Coma? Sugar is the body's main fuel. Sugar is burned by the cells to produce energy. However, sugar cannot be used for fuel when too little insulin is present to get the sugar into cells. Instead, the sugar stays in the blood. Since the body needs fuel to keep going, it has to turn to another fuel source when sugar is not available. That fuel is body fat. The problem is that when the body burns fat, it forms waste products called ketones. Ketones build up in the blood and spill into the urine. Because these ketones are more acidic than healthy body tissues, high blood levels of ketones may lead to a serious condition called ketoacidosis and to diabetic coma. Guidelines for Ketone Testing Test your urine for ketones when: Your blood sugar is over 300 mg/dL for 2 consecutive tests. You feel sick, have a cold, flu, or an infection. You are vomiting or feel sick to your stomach. You have symptoms of high blood sugar or ketoacidosis. You are under extreme stress. If you find ketones in your urine, it is a sign that you need to improve your blood sugar control. You may need to change your insulin dose or food choices. Contact the Diabetes Center for advice.