Detection of haemolysis and reporting of potassium results in samples from neonates

Abstract

In vitro haemolysis is a common occurrence in clinical laboratories and causes a spurious increase in potassium. In the past, haemolysis was sought by visual inspection but is now commonly detected by automated measurement of the haemolytic index (HI). This study compared detection of haemolysis in adult and neonatal samples by inspection and measurement of HI and verified that a single equation is appropriate to correct for the increase in potassium in both haemolysed samples. Laboratory staff inspected samples for haemolysis and their observations were compared with the measured HI. The potassium concentrations and haemolytic indices of 613 adult and 523 neonatal samples were correlated to derive equations to compensate for the increase in potassium with increase in HI. These were found not to differ significantly and a single equation for use in both populations was derived. 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 micromol/L x 0.01). The use of HI rather than visual inspection is particularly recommended in neonates whose serum tends to be icteric. It can be used in the same correction equation as in adults to compensate for potassium released due to haemolysis and facilitate reporting a qualitative comment to assist in immediate clinical management.