Hyperkalaemia (raised serum potassium)

• No tests in the community: refer to the emergency department (continuous cardiac monitoring).
• Do an ECG if possible without delaying transfer.

Within 24 hours

• Serum electrolytes (repeat serum potassium)
• Serum creatinine with eGFR
• Bicarbonate
• Plasma glucose
• FBC (if the repeat serum potassium remains high with no obvious cause)if needednon-French guidelineHyperkalaemia with normal renal function and ECG, or known haematological disease: thrombocytosis, hyperleucocytosis or polycythaemia can cause a false hyperkalaemia ^[1,2].
• Draw blood from the antecubital fossa without clenching the fist, tourniquet released as soon as the vein is punctured (less than a minute); transport quickly to the laboratory, without refrigeration; note the time of sampling. If spurious hyperkalaemia is suspected: request serum potassium on serum and on plasma (heparinised tube) drawn at the same time.
• ECG the same day.

Within 3 days

• Serum electrolytes (repeat serum potassium)
• Serum creatinine with eGFR
• Bicarbonate
• Plasma glucose
• FBC (if the repeat serum potassium remains high with no obvious cause)if needednon-French guidelinePersistent hyperkalaemia with normal renal function and ECG, or known haematological disease: thrombocytosis, hyperleucocytosis or polycythaemia can cause a false hyperkalaemia ^[1,2].
• 8 am serum cortisol (if hyperkalaemia confirmed with no renal failure or causative drug)if needednon-French guidelineUnexplained true hyperkalaemia, all the more so with hyponatraemia, asthenia, weight loss, hypotension or melanoderma: Addison's disease (primary adrenal insufficiency) is one cause ^[1].
• Draw blood without clenching the fist, tourniquet released as soon as the vein is punctured; transport quickly, without refrigeration; note the time of sampling.