Three case studies are described for patients presenting with ketosis. Patients have medical histories of type 1 diabetes and type 2 diabetes. These patients present with elevated blood and urine ketones associated with diabetic ketoacidosis (DKA), alcoholic ketosis, and starvation-induced ketosis with a possible component of DKA. The metabolism of ketones and the physiology of DKA are described, and the various laboratory methodologies for analyzing blood and urine ketone bodies are also reviewed.