Ketone bodies, also called acetone bodies or simply ketones, are any of three compounds produced when the liver metabolizes fatty acids. The three types of ketone bodies — acetoacetic acid, beta-hydroxybutyric acid, and acetone — are released into the bloodstream after metabolism occurs. Acetoacetic acid and beta-hydroxybutyric acid are used for fuel by the brain and muscles, but the body can't break down acetone and therefore excretes it in the urine. Excess acetone or ketones in the blood and urine can be a sign of a serious metabolic disease, and doctors often use the measurement of ketones as a tool in the diagnosis of such diseases.
In healthy individuals, the body uses mostly carbohydrate metabolism to fuel its cells. If sufficient carbohydrates are not available, such as during extreme starvation, the body begins metabolizing fats into ketone bodies to provide the necessary fuel. High levels of ketones in the urine, a condition called ketonuria, indicate the body is using mostly fat for its energy.
Another condition that will produce increased levels of ketone bodies is Type I diabetes — a severe form of diabetes mellitus. Individuals with diabetes mellitus are unable to efficiently metabolize glucose, typically because of insufficient insulin or insulin resistance. Their bodies will begin metabolizing fats and proteins to make up for the lack of available glucose for energy.
When doctors suspect diabetes, one of the first things they will check for is excess ketones in the urine. Performed with a simple urine dipstick, the test can quickly alert doctors to a metabolic disorder such as diabetes. High levels of ketones can also cause a person to have an acetone or fruity smell on their breath. Further tests of blood glucose levels can confirm the disease. The urine ketone tests are also useful in helping diabetic patients maintain proper diet and medication for optimal control of the disease.
Ketonuria may help signal possible complications during extreme fasting or fad diets, or during pregnancy. Testing of pregnant women is important because ketonuria has possibly been linked with some fetal deaths. Physicians also routinely screen acutely sick patients and patients who are preparing for surgery for indications of possible metabolic problems.
The presence of ketones in the blood or urine is not only a signal of metabolic problems. Ketones themselves can be dangerous in high levels. Without treatment, extremely high levels of ketones in the blood and urine can lower the blood's pH and cause a condition called ketoacidosis. It occurs most often in people with uncontrolled diabetes mellitus and is exacerbated when high blood glucose levels, caused by lack of available insulin, further acidify the blood. Ketoacidosis can lead to ketoacidic coma or death.