Clinical Review Lesson of the week

In vitro and in vivo haemolysis and potassium measurement

BMJ 2005; 330 doi: (Published 21 April 2005) Cite this as: BMJ 2005;330:949
  1. Abbas Ismail, consultant rheumatologist (,
  2. Wendy Shingler, specialist registrar in rheumatology1,
  3. Jeff Seneviratne, consultant clinical scientist1,
  4. Gillian Burrows, consultant chemical pathologist1
  1. 1Rheumatology Department, Stepping Hill Hospital, Stockport SK2 7JE
  1. Correspondence to: A Ismail
  • Accepted 24 November 2004


Serum or plasma potassium concentration is one of the most commonly requested biochemical tests. Haemolysis is common, occurring in vitro in most cases—that is, during or after taking the sample. In such cases, reported potassium concentrations are clinically inaccurate, greater roughly in proportion to the degree of haemolysis.13 The World Health Organization recommends that laboratories do not report potassium concentrations for haemolysed samples because of this.4

By not reporting a result, laboratories may imply to the clinical team that potassium concentration cannot be measured analytically. But in cases of in vivo haemolysis, a result may be of clinical use. We report a case of a patient with renal failure and in vivo haemolysis who subsequently died, which highlights the problems of not reporting potassium concentrations for haemolysed samples.

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