Spurious hyperkalaemia is common. Haemolysis during difficult venepuncture, a long tourniquet time or fist clenching, delay before the sample is separated, cold storage, and very high platelet or white cell counts all release potassium from cells after the blood has left the patient.
When the result does not fit the clinical picture, look for a haemolysis flag, check the ECG, and repeat the sample promptly, drawn without prolonged tourniquet and processed quickly. If the ECG shows changes of hyperkalaemia or the patient is at high risk, treat while waiting rather than after.
- Check the laboratory report for a haemolysis index or comment.
- Record an ECG when potassium is raised, whatever the suspected cause.
- Repeat the sample quickly with a short tourniquet time and no fist clenching.
- Consider spurious results in patients with very high platelet or white cell counts.
- Treat without waiting if the ECG is abnormal or the patient is at high risk.
Why it matters
Treating a spurious result can drop a normal potassium too low, while dismissing a real one can be fatal.
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