Hypokalaemia
Hypokalaemia is a serum potassium below 3.5 mmol/L, usually from gastrointestinal or renal loss or a transcellular shift; assess the ECG and symptoms urgently, replace potassium safely, correct magnesium and treat the cause.
Definition
Hypokalaemia is a serum potassium concentration below 3.5 mmol/L. The NHS Specialist Pharmacy Service groups adult hypokalaemia as mild at 3.0–3.5 mmol/L, moderate at 2.5–2.9 mmol/L and severe below 2.5 mmol/L; laboratory reference ranges and treatment thresholds should be interpreted with the clinical context.
First principles
Potassium controls electrical excitability
The potassium gradient across cell membranes helps set the resting membrane potential. Depletion reduces neuromuscular excitability, causing weakness, cramps, constipation or ileus; in cardiac muscle it disrupts repolarisation, producing characteristic ECG changes and increasing arrhythmia risk.
This page is exam revision material, not medical advice, and must not be used for patient care. Always check drug doses against the BNF and current guidance. Full disclaimer.