Drug Testing Using Hair: from an Expert Witness Perspective

By Lolita Tsanaclis PhD & John Wicks MSc, Directors, Cansford Associates Ltd, Cardiff, UK

Drug testing using hair shows what drugs have been used over an extended time-frame of months rather than days, which is the time-frame associated with urine and saliva (oral fluid) testing.  It is much more sensitive to occasional and intermittent use.  Where urine testing might miss a “party habit” every two weeks, hair testing will not.  It is this much improved confidence of detection that established the value of hair testing in Children at Risk cases.

Hair testing is the ideal sample when it is necessary to establish a pattern of use or non-use.  It will not tell whether an individual is under the influence now.  To assess if an individual is safe to drive or operate machinery, a urine or oral fluid test should be used.  To assess whether an individual is at risk or potentially at risk of working ‘under the influence’ a hair test is the best choice.

The retrospective window of detection is particularly valuable in those family cases where drugs are a risk factor.  A hair test can help to prove abstinence over months much more reliably than a urine test.  A single hair test may be more expensive than a single urine test but it requires at least 8 urine tests to be confident of surveying a month’s use or 25 tests for 3 months.  Also hair testing encourages compliance with court instructions as the only way that can guarantee beating the test is total removal of all hair.

When the hair sample is sufficiently long, multiple sections can be tested. Each section then represents blocks of several weeks and any changing pattern of drug use may be revealed, by detecting increasing or decreasing levels over longer time periods.

Hair testing cannot reveal on which day drugs were used.  It can give an indication but the evidence will be inevitably corroborative rather than definitive.  Similarly, the test will not give a precise answer to “how many times were drugs used?” or “what was the dosage used?”.  The testing laboratory should be able to give an indication, based on the cumulative results of its testing experience, of the level of drug use.  However all drug tests should be interpreted in the light of a clinical interview by a skilled drugs counsellor.

There are some factors that can affect the numerical result of a hair test like hair colour and hair treatments.  In general any treatment that damages the outer sheath of individual hairs may lead to loss of drug.  While in practice this is a relatively rare event it must always be considered.

Much of the basis for assertions of a racial bias with hair testing relate to the fact that non-white populations have a greater proportion of individuals with black hair.  Studies have shown no significant increase in detection of drugs in black haired individuals over others.  However the influence of hair colour does need to be considered.  We have personal knowledge of a case of a young man and woman who used drugs together and shared what they had.  He had dark black hair while she was a fine haired blonde.  Although their ‘habit’ was identical the test results were higher in him than in her.  This was explainable by their hair colour, not, as the court was tempted to conclude, by assuming a greater level of drug taking by the male.  A report on the effect of drugs used in each case is important to supplement the raw drug test result.

In cases where no head hair is available, body hair may be used but the time scales are much less clear.  In effect any drug found in body hair is ‘smudged’ over a much greater time-window, because the rate of growth is in effect much more variable, making any decision as to when drugs may have been used impossible.  However, there is potentially greater value in a negative drug result from body hair, like pubic hair, as the result represents a longer time period in comparison to head hair.

To distinguish between drug use and external contamination, a number of steps are taken.  The laboratory must wash the hair before analysis.  To prove ingestion of the drug, the laboratory must target metabolites that the body makes from the parent drug wherever possible.  The analysis of the residue from the wash and comparison with the drug concentration within the hair will demonstrate any significant contamination issues.  In our experience, external contamination is rare except in those individuals dealing in drugs and heavy users.

The value of a hair test is that it is very much more difficult to cheat than a urine test and much more sensitive to occasional sporadic use than an oral fluid test.  A urine or oral fluid test is certainly valuable in assessing compliance with treatment but when it is vital to know that an individual has not used drugs within a month or 3 month period a hair test is best.  And when the donor under test understands the power of the test it cuts out much debate about what they admit to having taken.  The whole process moves on to settling management regimes much more efficiently.

Posted in Did you know?, Editorials