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How accurate are hair follicle drug tests?
Hair drug testing is known as the gold standard in toxicological analysis, and is considered highly accurate for detecting drug use over an extended period.
It works by analysing a cut hair sample for the presence of drugs and their metabolites (breakdown products).
This article looks at hair drug testing in more detail, including accuracy, and how the test works.
- How can drugs be detected using drug testing?
- What is hair drug testing, and how does it work?
- How accurate is a hair follicle drug test?
- What factors can affect the accuracy of hair drug testing?
- What’s included in an AlphaBiolabs hair drug test report?
- What factors are considered when compiling a hair drug test report?
- Why are cut-off levels important for hair drug testing?
- Where can I get a hair drug test?
How can drugs be detected using drug testing?
When an individual consumes drugs, they are broken down by the liver and a proportion of the drug and its metabolites are then released into the bloodstream. A small amount of the drug is then excreted by the body in a variety of ways.
In hair, a proportion of the drug finds its way to the hair follicles and becomes trapped in the medulla, which is the innermost layer of the hair. It stays there as the hair grows. Similarly, in nails, a proportion of the parent drug and its metabolites travels to the nail beds and is trapped in the keratin fibres which span the entire length of the nail.
Due to the rate of nail and hair growth, these types of tests can detect drugs for up to 12 months after consumption. For oral fluid (saliva) drug tests, the window of detection is up to 48 hours after the drug has been consumed, and for urine drug tests it is up to 4 days.
What is hair drug testing, and how does it work?
Head hair drug testing involves a cut hair sample that is analysed for the presence of drugs and their metabolites. As mentioned above, when someone consumes drugs, a small amount of the drug and its metabolites travel to the hair follicle and become trapped. After 10 days, the hair containing the drug will have grown above surface levels and after an additional two weeks it is long enough to be included in a cut sample.
There are two types of head hair drug tests that can help us to determine a pattern of drug use over a specific period. These are segmented analysis and overview analysis.
Segmented analysis, which is the most detailed type of hair strand testing, requires the head hair sample to be in 1cm sections. These samples are then analysed to provide a month-by-month profile of an individual’s drug use. This is particularly beneficial for those who need to identify drug use patterns and can be used to determine a pattern for up to 12 months.
The other type of head hair drug testing is overview analysis, which provides a more general insight into someone’s drug use. In this method, the maximum length of hair that can be tested is 3cm, which provides an overview of 3 months. These profiles can be repeated up to four times to create a 3-monthly profile for up to 12 months. Unlike segmented analysis, overview analysis doesn’t specify which month the drug was likely to be taken; only whether the drug is detected in the specific sample provided.
If head hair is not available, body hair can be used as a sample. This is collected from the underarm, face, leg, back, arm or chest. Due to the growth rate of body hair, which differs from head hair, body hair samples cannot be segmented for a month-by-month profile. They can only be used to provide a general overview of up to 12 months of drug use. Body hair is collected by weight, rather than length of hair.
How accurate is a hair follicle drug test?
Our hair drug testing is 100% accurate and reliable based on the samples we receive at our laboratory. Here are just a few more reasons why you can trust the accuracy of AlphaBiolabs’ hair strand testing for court:
- We have over 15 years’ experience providing first-class drug testing services for the legal sector
- We have invested in the very latest drug testing technology for our state-of-the-art toxicology laboratory
- We employ some of the foremost scientists in Europe
- We follow cut-off guidelines for hair drug testing, as set by the Society of Hair Testing (SoHT)
- Our laboratory is accredited by UKAS to the quality technical standard of ISO 17025 (No. 2773) and certified to ISO 9001
- All our legal sample collections are carried out by professional sample collectors, under strict chain of custody conditions
- Our toxicologists work within the framework of Family Law and follow Part 25 of the Family Procedure Rules (2010)
What factors can affect the accuracy of hair drug testing?
It is widely known that certain hair treatments such as perming, straightening, bleaching, and dyeing can potentially impact hair strand test accuracy. This is because the chemicals used in these types of hair treatments can damage the hair shaft and alter the concentration of the drug.
For this reason, reputable testing laboratories like AlphaBiolabs always require a full disclosure of any recent hair treatments, so that this can be taken into consideration when preparing hair drug testing results. We will also record details of any medical conditions as well as any medications taken.
Trained sample collectors at AlphaBiolabs are also fully aware of the ways that individuals may try to ‘cheat’ hair drug tests, including trying to use a pre-cut sample that isn’t theirs or wearing a wig, and can therefore mitigate any attempts to ‘cheat’ the test.
Drugs can potentially be transferred to the outside of the hair through smoke or via direct contact. Therefore, when the hair samples arrive at our laboratory, they are always chemically washed three times to remove any surface layer drugs. This washing solution is then kept for further analysis, if required.
What’s included in an AlphaBiolabs hair drug test report?
We are committed to delivering scientifically robust and transparent drug test results.
Our reports provide context and expert interpretation, ensuring that results are not taken at face value but considered holistically.
Our hair drug test reports include:
- Sample donor information – including photo ID, and details of any disclosures made at the time of the sample collection (e.g. prescribed medications, drug/alcohol usage, environmental exposure to illicit drugs/close body contact with a drug user).
- Substances found and detected levels – which drugs have been detected, along with their concentration levels, measured in nanograms per milligram (ng/mg) or picograms per milligram (pg/mg) of hair (analyte dependent).
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Comparison with internationally-recognised cut-off levels – to ensure accuracy, the levels of substances detected are compared against scientifically validated thresholds. These cut-off levels play a fundamental role in helping to distinguish between actual drug use and potential external contamination.
AlphaBiolabs also has analytical cut-offs for each analyte that are higher than the SoHT cut-offs to take into account analytical variation. Therefore, when a positive result is reported, there is no doubt that the compound is present within that tested sample.
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Interpretation of the test results, including relevant caveats and considerations – a drug test report should not simply tell you whether the sample donor has tested positive or negative for a certain substance.
Our reports include expert analysis, considering factors such as possible external exposure to illicit substances, sample donor declarations, the presence of metabolites (which indicate active drug use), pattern assessments of active and previous drug use, and consideration of the natural variations in hair drug incorporation and rates of hair growth.
- Segmented analysis – if requested, hair samples can be segmented to provide an insight into a pattern of drug use over time, rather than a single result for the entire period (overview analysis).
- Contextual considerations – factors such as hair treatments, hair colour, sample donor declarations (such as prescribed medications/declared substance use), and the donor’s ethnicity are all carefully considered, to ensure a fair and accurate interpretation.
What factors are considered when compiling a hair drug test report?
The results of a hair drug test should never be interpreted in isolation. Several factors can influence how drugs are incorporated into the hair, meaning expert analysis is essential to ensure a fair and accurate assessment.
Factors that AlphaBiolabs’ Reporting Scientists will always consider when reporting hair drug test results, include:
- Hair type and colour – melanin levels in hair can impact drug incorporation, meaning darker hair may sometimes retain higher concentrations of certain substances.
- Cosmetic treatments – chemical treatments such as excessive bleaching, dyeing, perming or straightening have the potential to affect drug retention in hair strands.
- External contamination – environmental exposure to drugs (e.g. through smoke or physical contact) does not necessarily indicate use. Our reports consider the presence of metabolites – byproducts produced by the body after drug use – to help distinguish between active consumption and contamination. We also ensure the hair being tested is thoroughly washed first to ensure any surface contaminants are removed/minimised.
- Biochemical properties of drugs – different drugs bind to hair at different rates, meaning some substances are more likely to be retained than others.
- Variable growth rates of hair – Hair typically grows at an average rate of approximately 1 cm per month, as referenced by the Society of Hair Testing (SoHT). However, this rate can vary between individuals due to factors such as age, genetics, medical conditions, and ethnicity, potentially affecting the approximate time period represented by each hair segment.
Why are cut-off levels important for hair drug testing?
Cut-off levels play a crucial role in ensuring the accuracy and fairness of hair drug testing. Without cut-off levels, even trace amounts of substances could be reported, potentially resulting from passive exposure to drugs rather than active drug use.
One example of such a scenario is the ‘cocaine kiss’.
Cocaine can dissolve in saliva and be absorbed through the soft tissues in the mouth. This means that even a small amount of cocaine has the potential to be transferred to a non-cocaine user, through kissing.
Due to the sensitivity of modern-day drug testing, this can result in the person testing positive for cocaine even if they did not actively use the drug themselves.
At AlphaBiolabs, we follow internationally-recognised cut-off guidelines set by the Society of Hair Testing (SoHT), which bases its recommendations on extensive research across a diverse range of populations.
These scientifically established thresholds are:
- based on data from thousands of cases, covering a wide range of sample donors.
- reviewed regularly to reflect advancements in drug testing technology
- designed to distinguish between actual drug use and incidental environmental exposure, preventing misleading conclusions
Our reports are not just data-driven but include expert analysis to help clients understand the significance of the results. Where results are close to the cut-off level, we provide additional insights to prevent misinterpretation.
Where can I get a hair drug test?
AlphaBiolabs has extensive experience providing drug testing services for local authorities, family law professionals and social workers. We have invested in the very latest technology for our state-of-the-art toxicology laboratory, employing the very best scientists, so you can be confident of receiving a 100% accurate result.
We have a nationwide network of professional sample collectors, and all sample collections are performed under strict chain of custody conditions.
We also offer free sample collection for legally-instructed hair drug tests from our Dublin walk-in centre.
For expert advice on hair drug testing, or to request a quote, call AlphaBiolabs’ Legal team on 0140 29466 or email testing@alphabiolabs.com.
Alternatively, complete our online quote form, and a member of the team will be in touch to discuss your needs.
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Gail Evans
Technical Trainer at AlphaBiolabs
A professionally-trained forensic scientist, Gail joined AlphaBiolabs in 2012 and holds the role of Technical Trainer.
Her day-to-day responsibilities include delivering in-depth training sessions both internally and externally, covering DNA, drug, and alcohol testing.
Throughout her career at AlphaBiolabs, Gail has held a variety of roles, including within the Legal and Workplace sectors of the business.
Before joining the company, Gail was a practicing forensic scientist with 25 years’ experience working for the Forensic Science Service, attending scenes of crime, and analysing physical and biological material with potential evidential value.
Gail also holds qualifications in chemistry and is a Lead Auditor for the ISO 9001 standard, the international standard for quality management.
