Potassium is the most abundant intracellular electrolyte in the body and is critical for the function of every cell, particularly nerve and muscle cells. The kidneys maintain tight control of blood potassium — excreting excess in urine or retaining it when levels are low — ensuring levels stay within a narrow life-sustaining range.

Both high potassium (hyperkalaemia) and low potassium (hypokalaemia) can cause serious and potentially fatal cardiac arrhythmias. Hyperkalaemia is most commonly seen in kidney disease, where the kidneys can no longer excrete excess potassium, or with certain medications (ACE inhibitors, potassium-sparing diuretics). Hypokalaemia occurs with vomiting, diarrhoea, diuretic use, or inadequate dietary intake.