Ethanol concentration changes in blood samples during medium-term refrigerated storage

Stability of blood alcohol concentration (BAC) in laboratory samples is of great importance when it is necessary to perform repeated analyses.

We have analyzed the stability of BAC in 50 samples, which were taken from apprehended drivers, kept at -18ºC, without preserving agents. Quantitative analyses were performed using headspace sampling gas chromatography (HS-GC) with flame ionizing detection (FID). Samples were analyzed immediately after collection (C1), and after 60 (C60), 120 (C120) and 180 (C180) days. A group of 50 samples, which were kept closed for 180 days at -18ºC, was utilized as a control.

We found a significant decrease in BAC between C1 and C180 (= 0.224; SD= 0.144; t = 10.98; p<0.001), and between C1 and C60, C60 and C120, C120 and C180. There was a significant positive correlation (r=0.8) between starting concentration C1, and the value of BAC changes (ΔC). Linear regression analysis (R2=0.64) implies the degree of validity to the proposed model of ΔC change regarding initial BAC. There were significant changes in ΔC between the two groups.

These data underline the significance of air chamber percent (CA%) and ethanol evaporation due to ventilation between liquid and gas phase as a mechanism of ethanol decay.