Artefactual reduction in plasma total carbon dioxide concentration in children

Abstract

Methods The effect on plasma total carbon dioxide (ctCO₂) of collecting a small volume of blood into a large tube was investigated. In a 7-month-old infant presenting with diarrhoea the initial ctCO₂ was low when 0·3 mL of sample was received in a 4-mL tube. To investigate this further blood samples were obtained from three volunteers on five occasions and various volumes were placed in a 4 mL container and analysed after varying intervals. Results When the sample volume was less than 2 mL there was a significant decrease in ctCO₂. A 42% decrease was seen in the tube containing 0·3 mL after 4 h. Conclusions We recommend that when a small volume of sample is collected it should be placed in a smaller tube with minimal air space.