Your system produces ketone bodies when your liver breaks down fatty acids in a state of low glucose levels. In total, there are three ketone bodies: acetoacetate (AcAc), beta-hydroxybutyrate (BHB), and acetone. 

AcAc is the primary ketone body in the urine. BHB is the primary ketone body in the blood (and also the most critical and predominant ketone in a healthy state of ketosis). And acetone is the primary ketone body in the breath.