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)
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