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

For a patient presenting with hypokalaemia in primary care, the recommended initial investigations include:

• Repeat serum potassium measurement to confirm hypokalaemia and exclude spurious results or rapidly decreasing potassium levels that require urgent hospital admission.
• Assess serum magnesium levels, as hypomagnesaemia often coexists with hypokalaemia and must be corrected to effectively treat potassium deficiency.
• Review and consider stopping or adjusting medications that may contribute to hypokalaemia, such as thiazide or loop diuretics, and consider switching to potassium-sparing diuretics if appropriate.
• Investigate for underlying causes if hypokalaemia persists after medication review, including possible endocrine causes or dietary insufficiency.
• Consider additional blood tests based on clinical context, such as renal function tests and acid-base status, to identify causes like renal potassium loss or metabolic alkalosis.
• Recheck serum potassium after 2 weeks or sooner based on clinical judgement to monitor response to treatment or progression.

Referral to a specialist or secondary care is advised if hypokalaemia is severe (<2.5 mmol/L), symptomatic, or if the cause remains unclear after initial investigations.

Oral potassium chloride supplementation may be initiated in primary care for mild to moderate hypokalaemia, with repeat potassium measurement 3–4 days after starting treatment to guide dosing.

These recommendations are based on the British Medical Journal Best Practice guidelines and expert opinion as summarized in the NICE Clinical Knowledge Summary on Hypokalaemia NICE CKS.