When the body is unable to get energy from glucose – often because there’s not enough insulin to move it out of the blood and into the cells – it starts to break down fat for fuel. Ketones are substances created during this fat breakdown. A buildup of ketones is harmful and can lead to a serious condition called ketoacidosis. There are some at-home test kits you can use to check for ketones in the urine. Test for ketones if you have high blood sugar (greater than 300 mg/dL); are sick, feel nauseous, or are vomiting; or if you are overly thirsty. Contact your healthcare provider if results show moderate or large ketones present.