Hair drug testing is routinely used in the field of family law and is considered the gold standard for providing a history of drug abuse. Head hair grows at an average rate of 1 cm each month; therefore, drug use can be established over a defined period depending on the length of hair selected. However, the accuracy of any hair drug analysis depends on both the sampling procedure and the laboratory techniques employed.
Getting a sample
Hair strand samples are normally collected by a trained sample collector. The sample needs to be cut from the highest point of the scalp and needs to contain around 200 individual strands (about the width of a pencil). Ideally, it should be taken from a discrete area.
If head hair is not available alternative collection sites could be considered including pubic, underarm, chest, leg and beard hair. The growth rate of hair from these alternate sites differs from head hair and as such body hair cannot be used to determine a specific timeframe of drug use.
Which type of head hair drug test?
There are two types of head hair drug tests available: overview or segmented analysis.
An overview analysis can provide a general indication of drug use. This could range from 3 cm to identify drug use within that 3-month time period, up to 6 or even 12 months, dependent on the length of hair available. In an overview test, any episodes of drug taking are averaged out over the period being tested. For example, if an individual has not taken drugs for 5 months but then takes an excessive amount in 1 month, drug markers will be found along the entire length of the hair.
Segmented analysis provides a more detailed analysis and the episode of drug taking can be pinpointed to the actual month. In a 6-month segmented analysis, hair samples can be sectioned into six measured segments of 1 cm to provide six individual monthly analyses. As such, segmented analysis is especially useful if you need to obtain a trend in drug use, such as to see a decrease or increase, or to highlight intermittent use.
Segmented vs. overview?
Deciding on which type of hair drug testing to choose in legal cases can have major implications. If an overview test is selected, even if an individual uses drugs occasionally, the test may come back positive for the whole period. This result implies that the sample donor had been abusing drugs during the whole period analysed.
To overcome this, segmented hair drug testing could be performed over the same period. This would provide a more accurate assessment of the individual’s drug abuse/abstinence when presented to the court for scrutiny.
Cases such as this demonstrate the importance of expert advice when choosing the appropriate test to avoid misleading results.
Your client doesn’t have any hair? That’s not a problem. Other drug testing methods are available such as nail clipping analysis.
A more in-depth version of this article on hair drug testing can be read on our Learning Centre.
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Whilst every effort is made to ensure that the information is correct, no warranty, express or implied, is given as to its accuracy and no liability is accepted for any error or omission.
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