This was the resounding message from the recent, and excellent, Family Law Bar Association seminar on drug testing led by Sarah Branson, barrister at Coram Chambers and Paul Hunter Technical Director at Forensic Testing Service Ltd.
Most practitioners are aware that there is a raft of authorities which make it clear that Hair Strand Testing has its limitations and should never be regarded as determinative or conclusive – such authorities including:
Re D (Children Interim Care Order Hair Strand Testing) [2024] EWCA Civ 498
London Borough of Islington v M and another [2017] EWHC 364 (Fam) (Hayden J) and
Re H (A Child: Hair Strand Testing) [2017] EWFC 64
I suspect however that most practitioners do not realise the number of variables, outside of the variation between laboratories, which can affect the results nor the extent to which such variables can impact the results.
Factors that may impact significantly on test results include the well-known “hair dye” (the use of bleach and permanent hair dye can remove up to 80% of drug from hair) as well as lesser-known factors such as the hair collection site (from different parts of the scalp), natural hair colour, ethnicity and the use of thermal straighteners.
It was made abundantly clear during the lecture that if the testing laboratories use cut-offs and rely on the test result in isolation to form their opinions, the evidence will be unreliable.
Figures of false reporting arising from the use of cut off figures for approximately 3000 samples in cases with known and supported outcomes included 20% of samples from chronic cocaine users being reported as “negative” and 18% of samples from people not using cocaine having returning a “positive” result. In relation to the testing for cannabis use 60% of the hair samples taken from chronic cannabis users returned a “negative” result for the drug.
The expert needs to consider the context and chain of evidence that might impact the results and the interpretation in each case. To be able to do so there needs to be proper instruction from the start so that the expert can establish and consider all the influencing factors. These will include a detailed profile of declared use of drugs, medications and/or alcohol and also the client’s natural hair colour and ethnicity, information about exposure to drugs for instance from where the client is living or working, photographs of the sample collection showing the site of collection together with the length of hair that has been left on the scalp and information about cosmetic or other treatments to include the use of hair straighteners.
We were also reminded to consider asking the expert to take samples as required for their investigation to include nail samples which could be particularly important if your client is saying that a positive result is due to contamination rather than use.
For those interested in learning more we were told that there will be a Resolutions Podcast on the issue coming up soon.
