Overview vs. Segmented: Hair drug testing explained by AlphaBiolabs

Hair drug testing is routinely used in family law to provide a history of drug abuse. Unlike oral fluid and urine drug testing, which only give a short-term measure of drug use (usually a few days or weeks), hair strand testing can determine a history of drug intake for up to 12 months. Drugs remain relatively stable in hair and thus hair strand testing can effectively confirm long-term exposure to drugs over a defined period depending on the length of hair collected.

When a drug is ingested, it is absorbed into the bloodstream. Drugs and their metabolites are then absorbed through the root of the hair and become embedded in the hair shaft. These metabolites remain in the hair as it grows. This makes hair strand testing a suitable method for detecting a person’s historical drug intake on a month-by-month basis. However, hair strand analysis cannot show recent drug history: it can take between 7–10 days for the hair containing the drug to grow above the scalp.

Overview or segmented?

There are two types of head hair drug tests available: overview or segmented analysis. 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.

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 (2 x 3) or even 12 (4 x 3) months, dependent on the length of hair available. Differing results from the 3-month overviews can help highlight patterns in drug use.

Segmentation provides a more detailed analysis in which the episode of drug taking can be pinpointed to the actual month. The head hair samples are segmented into monthly 1 cm sections to provide a month-by-month profile of drug use. In cases where a single administration of a particular drug is suspected, the analysis of small segments can help establish a positive hair test in a narrow timeframe.

Segmented analysis is especially useful if you need to obtain a trend in drug use, such as to see a decrease or increase in drug use over time, or to highlight intermittent use.

Choosing which test can have legal implications

Deciding on which type of hair drug test to choose in family law cases can have major implications. If a 3-month overview drugs of abuse test is selected, even if an individual uses drugs occasionally, the test may come back positive for the whole 3-month 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 3-month period. The sample donor could show positive one month and negative the other 2 months. 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 an expert advising on the appropriate test to use. Taking an average of drug levels in a specified hair section without the knowledge of levels in the hair section prior to the period of interest can produce misleading results.

The table below is an example of the hair analyses regularly performed by AlphaBiolabs.

Analysis type required
Number of segments
Reported time period
Type of test
3 months
3 individual months
2 x 3-month periods
6 individual months

What is the sample collection procedure?

The accuracy of any hair drug analysis depends on both the sampling procedure and the laboratory techniques employed. Hair strand samples should be collected by a trained sample collector.

The hair sample needs to be cut from the highest point of the scalp (the vertex) as this region is associated with least variation in growth rates. Ideally, the sample needs to contain around 200 individual strands (about the width of a pencil) and should always be taken from a discreet area.

Excessive shampooing, some cosmetic treatments (such as dyeing, bleaching, perming and relaxing), and the use of thermal straighteners may reduce drug concentrations in hair to varying degrees. The extent of the loss will depend on the cosmetic treatment used and the drug present. All hair treatments should therefore be declared at the time of sample collection and taken into consideration when reviewing the findings of a hair test.

If the tested individual has been in an environment heavily laden with a drug, detectable levels could be found in the hair sample due to smoke. In addition, it could be transferred by direct contamination (such as by hands). To avoid any such false positive results, each hair sample is chemically washed three times to remove or reduce any drug present prior to analysis. The washing solution can also be analysed if required. For example, if an individual admits to being surrounded by cannabis smokers, the washing solution could be used to back up the test results. Any external exposure to drugs should be declared at the time of sample collection.

In addition, the Society of Hair Testing (SoHT) Guidelines for Drug Testing in Hair provide recommended cut-off levels to follow [1].

If head hair is not available alternative collection sites on the body could be considered including chest, back, arm, underarm and leg hair. The growth rate of hair from these alternate sites differs from head hair and as such cannot be used to determine a specific timeframe of drug use. However, they can provide up to a 12-month overview of drug use. Beard hair grows at a rate of 0.7 cm a month, so analysis of this type of hair can provide a more specific timeframe. Different types of body hair cannot be combined in one sample. Approximately 20–30 mg of sample needs to be collected.

AlphaBiolabs has an in-house toxicology team and Customer Services department that can provide expert advice on hair drug testing. If you have any queries, please call 0333 600 1300 or email info@alphabiolabs.com

We also offer other drug testing solutions including oral fluid, urine and nail clipping analysis.

[1] http://www.soht.org/component/content/article/9-nicht-kategorisiert/85-statement-2011