The phrase "ketone in the blood" refers to a high level of ketones present in the bloodstream. Ketones are chemicals that are produced when the body breaks down fats for energy, particularly during periods of fasting or prolonged exercise. In normal circumstances, ketones should not be detected in the blood as they are quickly removed by the kidneys and excreted through urine. However, if there is a high level of ketones present in the blood, it can indicate that the body is producing too many ketones or that the liver is unable to process them properly. This condition is known as diabetic ketoacidosis (DKA) and can be a serious complication for people with diabetes if left untreated.