Ann Clin Biochem 2009;46:222-225
doi:10.1258/acb.2009.008241
© 2009 Association for Clinical Biochemistry
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Original Articles
Jinny Jeffery,
Aabha Sharma and
Ruth M Ayling
Department of Clinical Biochemistry, Derriford Hospital, Plymouth PL6 8DH, UK
Corresponding author: Dr Ruth M Ayling. Email: ruthayling{at}clinicalbiochemistry.org.uk
Background: In vitro haemolysis is a common occurrence in clinical laboratoriesand causes a spurious increase in potassium. In the past, haemolysiswas sought by visual inspection but is now commonly detectedby automated measurement of the haemolytic index (HI). Thisstudy compared detection of haemolysis in adult and neonatalsamples by inspection and measurement of HI and verified thata single equation is appropriate to correct for the increasein potassium in both haemolysed samples.
Methods: Laboratory staff inspected samples for haemolysis and theirobservations were compared with the measured HI. The potassiumconcentrations and haemolytic indices of 613 adult and 523 neonatalsamples were correlated to derive equations to compensate forthe increase in potassium with increase in HI. These were foundnot to differ significantly and a single equation for use inboth populations was derived.
Results: The presence of icterus was found to decrease ability to detect haemolysis on inspection. The mean (95% confidence limits) potassium increase per unit HI was 0.0094 mmol/L (0.0078–0.0103 mmol/L) for adults and 0.0108 mmol/L (0.0094–0.0121 mmol/L) for neonates. The equation developed to compensate for potassium release in haemolysed samples was: adjusted potassium = measured potassium – (HI in µmol/L x 0.01).
Conclusion: The use of HI rather than visual inspection is particularlyrecommended in neonates whose serum tends to be icteric. Itcan be used in the same correction equation as in adults tocompensate for potassium released due to haemolysis and facilitatereporting a qualitative comment to assist in immediate clinicalmanagement.
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