University of Ottawa, Canada.
University of British Columbia, Canada.
Accid Anal Prev. 2022 Aug;173:106694. doi: 10.1016/j.aap.2022.106694. Epub 2022 May 26.
Cannabis is the second most commonly used impairing substance by drivers, after alcohol. As more countries legalize cannabis, there is concern that cannabis-impaired driving will increase. In many countries, police use roadside devices to test for oral fluid THC (the primary psychotropic component in cannabis) to identify drivers who used cannabis; including in countries with non-zero per se limits for THC in blood. This practice is questioned as previous research demonstrates a poor correlation between oral fluid and blood THC concentrations at the individual level. We conducted a meta-analysis to identify all research that compared oral fluid with blood THC levels. We obtained individual-level data from study authors and analyzed pooled individual-level data to calculate sensitivity and specificity of oral fluid THC (at various cut-off values) to detect blood THC above different concentration limits. Finally, we explored practical implications of using oral fluid THC in an enforcement context. Our review found THC concentrations measured in over 18,000 paired samples of oral fluid and blood. We found a good correlation between the presence of THC in oral fluid and presence of THC in blood (sensitivity = 71.2%, specificity = 97.7%). However oral fluid THC, at commonly used cut-off values, is less sensitive and less specific when used as a biomarker to detect people with blood THC concentrations above commonly used per se limits (such as 5 ng/mL). As such, there will be a large number of "false positive" tests if oral fluid THC testing were used as a biomarker for "illegal" THC concentrations in randomly selected drivers. We argue that the adverse implications of false positive oral fluid THC tests in this context outweigh the possible road safety benefits and we recommend against oral fluid THC screening in randomly selected drivers in countries with non-zero per se limits for blood THC. In contrast, oral fluid THC tests appear to be useful for investigating "high-risk" drivers who come to police attention because of evidence of impairment.
大麻是仅次于酒精的司机第二大常用致瘾物质。随着越来越多的国家使大麻合法化，人们担心大麻致醉驾驶的情况会增加。在许多国家，警察使用路边设备检测口腔液中的 THC（大麻中的主要精神活性成分），以识别使用过大麻的司机；包括在血液中 THC 有非零法定限制的国家。这种做法受到质疑，因为先前的研究表明，个体水平上口腔液和血液 THC 浓度之间的相关性较差。我们进行了一项荟萃分析，以确定所有比较口腔液和血液 THC 水平的研究。我们从研究作者那里获得了个体水平的数据，并对汇总的个体水平数据进行了分析，以计算不同截止值下口腔液 THC（检测不同浓度限制以上的血液 THC）的敏感性和特异性。最后，我们探讨了在执法背景下使用口腔液 THC 的实际意义。我们的综述发现，在超过 18000 对口腔液和血液的 THC 浓度进行了测量。我们发现，口腔液中 THC 的存在与血液中 THC 的存在之间存在良好的相关性（敏感性为 71.2%，特异性为 97.7%）。然而，当作为生物标志物检测血液 THC 浓度高于常见法定限制（如 5ng/ml）的人时，常用截止值下的口腔液 THC 检测的敏感性和特异性较低。因此，如果将口腔液 THC 检测用作随机选择的司机中“非法” THC 浓度的生物标志物，将会有大量的“假阳性”检测。我们认为，在这种情况下，假阳性口腔液 THC 检测的不利影响大于可能的道路安全益处，我们建议在血液 THC 有非零法定限制的国家，不要对随机选择的司机进行口腔液 THC 筛查。相比之下，口腔液 THC 检测似乎对因损伤证据而引起警察注意的“高危”司机有用。
