U.S. Federal Bureau of Investigation, Laboratory Division, 2501 Investigation Pkwy, Quantico, VA 22135, USA.
Forensic Sci Int. 2011 Jul 15;210(1-3):110-6. doi: 10.1016/j.forsciint.2011.02.015. Epub 2011 Mar 6.
Segmental analysis of hair for drugs, metabolites, and poisons has been widely reported in the scientific literature over the past two decades. Two fundamental assumptions in interpreting results of such analyses are (1) an average linear growth rate of head hair of 1cm/month and (2) that sample collections occur with the hair being cut directly next to the scalp. The purpose of this study was to evaluate the variability associated with growth rate of human head hair, as well as the ability to uniformly collect hair next to the scalp. The results were used to determine how these factors affect the interpretation of results generated in segmental analysis of hair. A thorough literature review was conducted to assess the range of linear growth of human head hair from the vertex posterior and occipital regions. The results were compiled to establish the average (1.06cm/month), as well as the range of possible growth rates of head hair. The range was remarkable and suggests that conclusions based on the 1-cm/month growth rate could be significantly skewed. A separate study was undertaken to evaluate collection of hair next to the scalp. Fourteen individuals were provided oral instructions, as well as a written standard collection procedure for head hair. The experience levels among the collectors varied from novice to expert. Each individual collected hair from dolls with short- and long-hair. Immediately following each collection, the sampling area was evaluated to determine how close to the scalp the cuts were made, as well as the variability in the lengths of hair remaining at the sampled area. From our collection study, we determined that 0.8±0.1cm of hair was left on the scalp after cutting. When taking into account the amount of hair left on the scalp after collecting, the use of a growth rate of 1.06cm/month, and the assumption that it takes two weeks for newly formed hair in the follicle to reach the scalp, we find that the first 1-cm segment of hair typically corresponds to hair formed 1.3±0.2 to 2.2±0.4 months (95% confidence) earlier. The impact of these findings as it relates to the corresponding time for each additional segment is demonstrated. As a result, we recommend that hair collection be delayed 8 weeks after a suspected ingestion to ensure that the sample fully represents the exposure period. The results of this study suggest that the variability in the growth rate of human head hair, as well as the inconsistent collection of hair, significantly affect the interpretation of results from segmental analysis of hair.
在过去的二十年中，分段分析头发中的药物、代谢物和毒物在科学文献中被广泛报道。解释此类分析结果的两个基本假设是：(1) 头部头发的平均线性生长速度为 1cm/月；(2) 样本采集是在头发紧贴头皮处进行的。本研究的目的是评估人类头部头发生长速度的可变性，以及紧贴头皮均匀采集头发的能力。结果用于确定这些因素如何影响头发分段分析中结果的解释。进行了全面的文献回顾，以评估人头顶和枕部头发的线性生长范围。结果汇总以确定平均生长速度（1.06cm/月）以及头发生长速度的可能范围。范围非常显著，表明基于 1cm/月的生长速度得出的结论可能会有很大的偏差。进行了另一项单独的研究来评估头皮附近头发的采集。为 14 个人提供了口头说明以及头部头发的标准采集程序。采集者的经验水平从新手到专家不等。每个人都从有短发和长发的娃娃上采集头发。在每次采集后，立即评估采样区域，以确定切口离头皮有多近，以及采样区域剩余头发长度的可变性。从我们的采集研究中，我们确定在切割后头皮上还剩下 0.8±0.1cm 的头发。考虑到采集后头皮上剩余的头发量、使用 1.06cm/月的生长速度以及假设新形成的毛囊中的头发需要两周时间才能到达头皮，我们发现第一个 1cm 的头发段通常对应于形成于 1.3±0.2 至 2.2±0.4 个月（95%置信区间）之前的头发。展示了这些发现对每个附加段相应时间的影响。因此，我们建议在怀疑摄入后 8 周再进行头发采集，以确保样本完全代表暴露期。这项研究的结果表明，人类头部头发的生长速度的可变性以及头发的不一致采集，会显著影响头发分段分析结果的解释。
