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Spurious hyperkalaemia

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

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spurious hyperkalaemia (pseudohyperkalaemia)

Spurious hyperkalaemia is described as laboratory-reported hyperkalaemia in a normokalaemic patient (1)

  • occurs when the reported laboratory potassium values do not reflect actual in vivo concentrations - usually because platelets, leucocytes, or erythrocytes have released intracellular potassium in vitro
  • it may result in major difficulties in primary care and unnecessary emergency referral and even admission to hospital

Causes may include:

  • collection and storage of specimen
    • higher temperatures or longer storage (overnight, for example) may lead to deterioration of the sample and large rises in potassium
    • potassium stored at an ambient temperature of 18°C for up to 16 hours has been reported to be stable
    • cold temperatures disable the membrane ATPase, leading to higher results
  • difficulty in collecting sample
  • excessive tourniquet or repeated fist clenching when sample was taken
  • sample was shaken or squirted through needle into collection tubes
  • contamination with anticoagulant from another sample (potassium EDTA)
  • cooling
  • deterioration of specimen due to length of storage
  • pre-existing conditions
  • thrombocytosis
  • severe leucocytosis (which can also produce pseudohypokaleamia)
  • hereditary and acquired red cell disorders (1,2)

If spurious hyperkalaemia is suspected:

  • artefactual causes should be considered if renal indices and serum bicarbonate is normal

  • consider causes such as
    • specimen was refrigerated or exposed to cold in transit
    • long delay between and venepuncture and separation
    • difficult venepuncture with prolonged tourniquet time
    • in vitro (sometimes in vivo) haemolysis
    • patients with raised blood cell counts (WBC >15x10^9, platelets >700x10^9/l)

  • take action
    • send a new sample for analysis within 3 hours of venepuncture
    • simultaneously measure potassium in plasma and serum; serum potassium concentration is usually 0.2-0.4 mmol/l higher than that in plasma, owing to release during normal clotting
    • remove tourniquet before drawing blood
    • do not allow specimen to cool below room temperature
    • if recent blood count is not available, send full blood count
    • if sequential samples are haemolysed, consider intravascular haemolysis
    • consider ECG in uncertain cases when potassium >6mmol/l (2)

Reference:


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