Dumlupinar University, Faculty of Medicine, Department of Medical Biochemistry, Kutahya, Turkey.
Dumlupinar University, Evliya Celebi Education, and Research Hospital, Department of Medical Biochemistry, Kutahya, Turkey.
Biochem Med (Zagreb). 2015;25(1):57-63. doi: 10.11613/BM.2015.006.
Measurements of blood ethanol concentrations must be accurate and reliable. The most important factors affecting blood ethanol stability are temperature and storage time. In this study, we aimed to compare ethanol stability in plasma samples at -20 °C for the different storage periods.
Blood samples were collected from intoxicated drivers (N=80) and initial plasma ethanol concentrations were measured immediately. Plasma samples were then stored at -20 °C and re-assessed after 2, 3, 4, or 5 months of storage. Differences between the initial and stored ethanol concentrations in each group (N=20) were analyzed using Wilcoxon matched-pairs test. The deviation from the initial concentration was calculated and compared with Clinical Laboratory Improvement Amendments (CLIA'88) Proficiency Testing Limits. Relationships between the initial concentrations and deviations from initial concentrations were analyzed by Spearman's correlation analysis. For all statistical tests, differences with P values of less than 0.05 were considered statistically significant.
Statistically significant differences were observed between the initial and poststorage ethanol concentrations in the overall sample group (P<0.001). However, for the individual storage duration groups, analytically significant decreases were observed only for samples stored for 5 months, deviations from the initial concentrations exceeded the allowable total error (TEa). Ethanol decreases in the other groups did not exceed the TEa.
According to our results, plasma ethanol samples can be kept at -20 °C for up to 3-4 months until re-analysis. However, each laboratory should also establish its own work-flow rules and criterion for reliable ethanol measurement in forensic cases.
血液乙醇浓度的测量必须准确可靠。影响血液乙醇稳定性的最重要因素是温度和储存时间。在这项研究中，我们旨在比较不同储存期时 -20°C 下血浆样本中乙醇的稳定性。
从醉酒司机（N=80）中采集血样，并立即测量初始血浆乙醇浓度。然后将血浆样本储存在-20°C 下，并在储存 2、3、4 或 5 个月后重新评估。使用 Wilcoxon 配对检验分析每个组（N=20）中初始和储存乙醇浓度之间的差异。计算初始浓度与储存浓度之间的偏差，并与临床实验室改进修正案（CLIA'88）能力验证限制进行比较。使用 Spearman 相关分析分析初始浓度与初始浓度偏差之间的关系。对于所有统计检验，P 值小于 0.05 的差异被认为具有统计学意义。
总体样本组中，初始和储存后乙醇浓度之间存在统计学显著差异（P<0.001）。然而，对于各个储存持续时间组，仅观察到储存 5 个月的样本有分析显著下降，偏离初始浓度超过允许的总误差（TEa）。其他组的乙醇下降未超过 TEa。
根据我们的结果，血浆乙醇样本可以在-20°C 下保存长达 3-4 个月，直到重新分析。然而，每个实验室还应制定自己的工作流程规则和标准，以确保在法医案例中可靠地测量乙醇。
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