In vitro and in vivo haemolysis and potassium measurement

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.1-3 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.