It is a strong organic acid and can be produced in the human liver under certain conditions of poor metabolism leading to excessive fatty acid breakdown (diabetes mellitus leading to diabetic ketoacidosis), it is then partially converted to acetone by decarboxylation and excreted either in urine or through respiration. The acid is also present in the metabolism of those undergoing starvation or prolonged physical exertion as part of gluconeogenesis. It is not the major ketone produced by the body (that being beta-hydroxybutyrate).
When ketone bodies are measured in a medical laboratory, acetoacetic acid is usually what is detected. This is done using dipsticks coated in nitroprusside. Nitroprusside changes from pink to purple in the presence of acetoacetate, and the colour change graded by eye.