Hyperkalaemia may be defined as a serum potassium concentration greater than 5.0 mmol/l. Since the vast majority of potassium is stored in the intracellular compartment, hyperkalaemia may reflect the redistribution of potassium into the extracellular space, rather than increased total body potassium. In some cases (e.g. in diabetic ketoacidosis), total body potassium may even be low.