Hypokalemia (American English) or hypokalaemia (British English), also hypopotassemia or hypopotassaemia (ICD-9), refers to the condition in which the concentration of potassium (K⁺) in the blood is low. The prefix hypo- means "under" (contrast with hyper-, meaning "over"); kal- refers to kalium, the Neo-Latin for potassium, and -emia means "condition of the blood."