Diagnostic Use
Increased plasma potassium is seen in:
- renal failure
- potassium supplementation
- ACE inhibitors, ARBs, aldosterone blockers
- Addison’s disease
- acidosis
- tumour lysis syndrome
Decreased plasma potassium is seen in:
- diuretics
- alkalosis (e.g. due to vomiting)
- chronic diarrhoea
- primary or secondary hyperaldosteronism
- treatment of diabetic ketoacidosis
- magnesium depletion
ARTEFACTUALLY INCREASED POTASSIUM
Intracellular K+ concentration is much higher than extracellular; a delay of more than 2 hours before separating the plasma can result in significant falsely increased K+ due to leakage out of cells. This effect is greater at low temperatures. Haemolysis also results in falsely increased K+.
PSEUDOHYPERKALEMIA
In some patients with leukemia, K+ leaks from white cells rapidly after the sample is taken; this effect is increased by clotting. The true K+ can be obtained by taking a heparinised blood sample and immediately analysing it on a blood-gas machine.
Test Method
Principle: Ion selective membrane
Analyser: Roche Diagnostics Cobas c703/c503
Limitations / Interference
Haemolysis during collection, delay in separation, refrigeration of unseparated blood, marked leucocytosis and thrombocytosis, and muscle activity of limb immediately prior to venepuncture may cause a misleading increase in potassium.
Uncertainty of Measurement
7.5% at 2.6 mmol/L and 2% at 7.5 mmol/L