Potassium Regulation

Potassium abnormalities become dangerous for two different reasons: the amount of potassium in the body may be abnormal, or potassium may move abruptly between the intracellular and extracellular compartments. A serum result is only a measurement of the extracellular fraction, so a high value can reflect cellular release, impaired renal excretion, or a collection error rather than a large total-body excess. Conversely, a patient may have substantial potassium depletion even when the serum concentration is temporarily near normal. Clinical reasoning therefore follows a sequence. First decide whether the result is credible, then assess the rhythm, symptoms, rate of change, kidney function, and likely cause. If hyperkalemia is causing cardiotoxicity, protect the myocardium and shift potassium into cells while arranging a way to remove potassium from the body. If potassium is low, replace it safely and look for magnesium deficiency when the value does not respond. This framework prevents two common errors: being reassured by a normal ECG or an apparently mild number, and mistaking a temporary intracellular shift for correction of the potassium burden.