Hypokalemia: A Clinical Update Hypokalemia, a condition where serum levels of potassium are lower than normal, is a common electrolyte disturbance. It usually results from increased potassium excretion or intracellular shift and less commonly from reduced potassium intake. An acceptable lower limit for normal serum potassium is 3.5 mmol/L. Severity is categorized as mild when the serum potassium level is 3 to 3.4 mmol/L, moderate when the serum potassium level is 2.5 to 3 mmol/L, and severe when the serum potassium level is less than 2.5 mmol/L. Values obtained from plasma and serum may differ. Compared to plasma levels, serum levels are usually slightly higher due to delay in processing and/or the effect of clotting.1,2 Symptoms and signs of hypokalemia can be subtle and easily overlooked without a carefully directed history and physical examination, and precise interpretation of the electrocardiogram (Box 1).3 Hypokalemia is more commonly associated with cardiac diseases, renal failure, malnutrition, and shock. Hypothermia and increased blood cell production are additional risk factors for developing hypokalemia. It is prevalent in hospitalized patients, in particular, pediatric patients, those who have fever and those who are critically ill.