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 NICE CKS, and supported by guidance on adrenal insufficiency investigations NICE NG243.