What are the recommended initial investigations for a patient presenting with hypokalaemia?

Recommended initial investigations for a patient presenting with hypokalaemia include:

• Repeat serum potassium measurement to confirm hypokalaemia and exclude spurious results or rapidly decreasing potassium levels.
• Serum magnesium concentration, as hypomagnesaemia often coexists and must be corrected to effectively treat hypokalaemia.
• Assessment of renal function and electrolytes including sodium, urea, and creatinine to evaluate fluid and electrolyte balance.
• Consider blood tests to identify underlying causes such as adrenal insufficiency (e.g., 8 am to 9 am serum cortisol) if clinically suspected.
• Review of medications that may contribute to potassium loss (e.g., diuretics) and clinical history for potential causes like poor intake or increased losses.
• ECG monitoring if clinically indicated to assess for cardiac effects of hypokalaemia.

These investigations help determine the cause and severity of hypokalaemia and guide appropriate management and referral decisions.

References: All recommendations are based on UK clinical guidelines and expert opinion as summarized in the NICE CKS topic on Hypokalaemia ¹, and supported by guidance on adrenal insufficiency investigations ².