Hypokalaemia is a condition characterised by a serum potassium concentration below 3.5 mmol/L, indicating a deficit of potassium in the extracellular fluid. It is clinically significant because potassium is essential for normal cellular function, particularly in cardiac and neuromuscular activity, and its imbalance can lead to serious complications. A key concern is the increased risk of cardiac arrhythmias, which can be life-threatening if not promptly recognised and treated.