Pre-analytical factors related to the stability of ethanol concentration during storage of ante-mortem blood alcohol specimens

Abstract

Sterile ante-mortem blood specimens were spiked with ethanol at the South African blood alcohol legal concentration limits of 0.20 g/L and 0.50 g/L and were stored in tubes containing sodium fluoride over a period of twenty-nine weeks under refrigeration (4 °C) and at room temperature (22 °C) to study the stability of the ethanol concentrations over time. Those stored under refrigeration were found to be stable, while a significant decrease in ethanol concentration at 99% confidence was observed in those stored at room temperature.Additional blood specimens, also spiked with ethanol, were inoculated with the dimorphic fungus Candida albicans at five different levels (1 × 106 cells/mL, 5 × 105 cells/mL, 1 × 104 cells/mL, 5 × 103 cells/mL and 5 × 101 cells/mL) and stored with and without sodium fluoride at 4 °C and 22 °C. The ethanol concentrations were monitored for nine weeks unless no fungal colonies were detected. Regardless of the presence or absence of NaF in samples – sterile or otherwise – storing specimens at 4 °C was sufficient to maintain the integrity of blood alcohol concentrations.The ethanol analyses were performed with an in-house validated isotope dilution gas chromatography-mass spectrometry analytical method on newly opened specimens once a week after which significance testing was performed to draw conclusions regarding changes in ethanol concentrations with measurement uncertainty in mind.