Intended for healthcare professionals

Practice Cases in primary care laboratory medicine

Spurious hyperkalaemia

BMJ 2007; 334 doi: (Published 29 March 2007) Cite this as: BMJ 2007;334:693
  1. W Stuart A Smellie, consultant
  1. Clinical Laboratory, Bishop Auckland General Hospital, Bishop Auckland DL14 6AD
  1. info{at}
  • Accepted 30 January 2007

Although severe hyperkalaemia is life threatening and a medical emergency, spurious hyperkalaemia (pseudohyperkalaemia) is common in blood samples taken in primary care, often because of sampling conditions and storage and transport problems

Pseudohyperkalaemia can cause major difficulties in primary care and is a source of avoidable emergency referral and even admission to hospital. It poses a particular problem in the context of out of hours services, when not all patient information is necessarily available to on-call doctors, and is a source of serious concern to patients. This article examines two situations in which apparently alarming hyperkalaemia may occur; it offers guidance to minimise the problem of pseudohyperkalaemia caused by in vitro release of potassium and on identifying the less common causes due to other disease.

Summary points

  • True hyperkalaemia is rare in the presence of normal renal function

  • Difficult venepuncture, cold storage, and deterioration of the sample all raise the serum potassium concentration and warm ambient temperature can lower it

  • Thrombocytosis can raise serum potassium

  • Severe leucocytosis can either raise or lower serum potassium depending on temperature conditions

  • Repeat sampling when results are suspect can avoid the distress of urgent hospital referral, at the same time excluding dangerous hyperkalaemia

  • A full blood count and parallel measurements of serum and plasma (lithium heparin) potassium are useful to identify spurious hyperkalaemia arising from intrinsic causes (blood dyscrasias, red cell abnormalities)

Case 1

A doctor responsible for clinical governance in a primary care practice contacted her local biochemistry laboratory to ask whether the laboratory had been experiencing problems with potassium measurement. Her practice partners had noticed several unexpectedly raised potassium results and one patient had recently been contacted urgently at 9 pm to be taken to hospital because a potassium result of 7.2 mmol/l had been telephoned to the out of hours service. This 72 year …

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