Beta-hydroxybutyrate (BOHB, also known as 3- hydroxybutyrate) is a ketone body produced when glucose cannot be used as a fuel source. It is measured in conjunction with free fatty acids (FFA) and glucose in order to investigate hypoglycaemia or symptoms associated with ketoacidosis. The ratio of FFA to BOHB in hypoglycaemia can help to detect hyperinsulinism or a fatty oxidation defect.