Kalium adalah kation yang paling umum terdapat dalam tubuh. Orang dewasa biasanya memiliki kalium antara 3 dan 4 mol, 98% terletak intraseluler. Kepentingan klinis Kalium berasal terutama dari kenyataan bahwa rasio kalium intraseluler ke ekstraseluler adalah penentu utama dari potensial membran istirahat (Em).

Hypokalemia

Hypokalemia is defined as a serum potassium concentration below 3.5 mmol/L. Hypokalemia has been reported to occur in 20% of hospitalized patients. However, this high number probably does not reflect total body potassium depletion. In a review of 70 hospitalized patients with potassium concentration below 2.8 mmol/L, the potassium concentration rose toward normal regardless of whether the patients were given potassium or not, although the use of intravenous (IV) potassium was associated with the faster rate of recovery. The authors suggested that hospitalization for acute illness was associated with increased adrenergic stimulation, resulting in intracellular movement of potassium and transient hypokalemia. Hypokalemia is also common in outpatients treated with diuretics. Hypokalemia was found in 11% of patients on 50 mg of hydrochlorothiazide.