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

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

MATERIALS AND METHODS: 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.

RESULTS: 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.

CONCLUSIONS: 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.