Houston Forensic Science Center, 500 Jefferson Street, 13th Floor, Houston, USA.
Center for Statistics and Applications in Forensic Evidence, 613 Morrill Road, Ames, USA.
J Anal Toxicol. 2019 Sep 10;43(8):630-636. doi: 10.1093/jat/bkz059.
Declared proficiency tests are limited in their use for testing the performance of the entire system, because analysts are aware that they are being tested. A blind quality control (BQC) is intended to appear as a real case to the analyst to remove any intentional or subconscious bias. A BQC program allows a real-time assessment of the laboratory's policies and procedures and monitors reliability of casework. In September 2015, the Houston Forensic Science Center (HFSC) began a BQC program in blood alcohol analysis. Between September 2015 and July 2018, HFSC submitted 317 blind cases: 89 negative samples and 228 positive samples at five target concentrations (0.08, 0.15, 0.16, 0.20 and 0.25 g/100 mL; theoretical targets). These blood samples were analyzed by a headspace gas chromatograph interfaced with dual-flame ionization detectors (HS-GC-FID). All negative samples produced `no ethanol detected' results. The mean (range) of reported blood alcohol concentrations (BACs) for the aforementioned target concentrations was 0.075 (0.073-0.078), 0.144 (0.140-0.148), 0.157 (0.155-0.160), 0.195 (0.192-0.200) and 0.249 (0.242-0.258) g/100 mL, respectively. The average BAC percent differences from the target for the positive blind cases ranged from -0.4 to -6.3%, within our uncertainty of measurement (8.95-9.18%). The rate of alcohol evaporation/degradation was determined negligible. A multiple linear regression analysis was performed to compare the % difference in BAC among five target concentrations, eight analysts, three HS-GC-FID instruments and two pipettes. The variables other than target concentrations showed no significant difference (P > 0.2). While the 0.08 g/100 mL target showed a significantly larger % difference than higher target concentrations (0.15-0.25 g/100 mL), the % differences among the higher targets were not concentration-dependent. Despite difficulties like gaining buy-in from stakeholders and mimicking evidence samples, the implementation of a BQC program has improved processes, shown methods are reliable and added confidence to staff's testimony in court.
声明的熟练程度测试在测试整个系统的性能方面是有限的，因为分析人员知道他们正在接受测试。盲法质量控制（BQC）旨在向分析人员显示为真实案例，以消除任何有意或潜意识的偏见。BQC 计划允许实时评估实验室的政策和程序，并监测案例工作的可靠性。2015 年 9 月，休斯顿法医科学中心（HFSC）开始进行血液酒精分析的 BQC 计划。在 2015 年 9 月至 2018 年 7 月期间，HFSC 提交了 317 个盲样：89 个阴性样本和 228 个阳性样本，浓度为五个目标浓度（0.08、0.15、0.16、0.20 和 0.25 g/100 mL；理论目标）。这些血样由顶空气相色谱仪与双火焰电离检测器（HS-GC-FID）分析。所有阴性样本均产生“未检出乙醇”的结果。上述目标浓度的报告血液酒精浓度（BAC）的平均值（范围）分别为 0.075（0.073-0.078）、0.144（0.140-0.148）、0.157（0.155-0.160）、0.195（0.192-0.200）和 0.249（0.242-0.258）g/100 mL。阳性盲样的 BAC 平均百分比差异在我们的测量不确定度（8.95-9.18%）范围内，从目标值的-0.4%到-6.3%不等。酒精蒸发/降解的速度被确定为可忽略不计。进行了多元线性回归分析，以比较五个目标浓度、八个分析人员、三个 HS-GC-FID 仪器和两个移液管之间的 BAC 差异百分比。除目标浓度外的变量无显著性差异（P > 0.2）。虽然 0.08 g/100 mL 目标的百分比差异明显大于较高目标浓度（0.15-0.25 g/100 mL），但较高目标之间的百分比差异与浓度无关。尽管存在获得利益相关者支持和模拟证据样本等困难，但 BQC 计划的实施改进了流程，表明方法可靠，并增加了员工在法庭上证词的可信度。
