How hair strand testing should be instructed for family court proceedings

SoHT cut-off levels are a benchmark for interpretation which can be set independently of whether a drug has been detected or not. If a drug has been detected, but below the cut-off, it will be reported as “Not Detected” or “Negative”- just like drugs which have not been detected at all.

Whilst the SoHT cut-off levels provide useful guidelines to aid interpretation, numerous factors influence measured drug concentration within an individual’s hair, and as such each case is unique. It therefore makes little sense to apply, as many labs do, a set threshold concentration as the single determining factor to decide if someone is a drug user.

Research from 1991, ten years after cut-off levels were introduced, demonstrates that the use of cut-off levels to interpret hair strand testing results discriminates against those who have darker hair, impacting black and ethnic minority backgrounds in particular.

FTS was curious what results we would get if we applied SoHT cut-off levels to some of own historical data. We took 3,000 of our previous cases where we had recorded outcomes from declared usage and other forms of testing (such as nail testing), then applied standardised cut-off levels to them. The results were startling:
• 12% hair samples in cases not using heroin came back Positive
• 18% hair samples in cases not using cocaine came back Positive
• 22% hair samples from chronic heroin users came back Negative
• 20% hair samples from chronic cocaine users came back Negative
• 60% hair samples from chronic cannabis users came back Negative

At first glance, such results may suggest that hair strand testing evidence is unreliable. But this is not the case. The authorities of Re D (Children: Interim Care Order: Hair Strand Testing) [2024] EWCA Civ 498 underscore the case of H (A Child – Hair Strand Testing) [2017] EWFC 64 in establishing the science behind hair strand testing as sound. It also makes clear that hair strand testing is opinion or expert evidence and needs to be looked at in the context of the wider evidential picture.

In other words, the science behind hair strand testing is reliable, but the interpretation of that evidence must be carried out with care and fully contextualised to avoid results being viewed as “pseudo-certainty”. Our results clearly show how, when cut-off levels are applied with little regard to the specificities of each individual’s case, results can mislead. When the results from testing of hair are interpreted simply by reference to standardised cut-off levels, such false positives and negatives will arise. As such, there is a risk of miscarriages of justice when hair strand testing is treated in isolation and not contextualized.

The alarming results above show how important it is that hair strand testing is properly instructed from the outset, with full regard for the client’s individual circumstances, including factors like hair colour, lifestyle, passive exposure and hair treatments, among others, and for this evidence to be treated as expert opinion evidence, not just as numbers.

As a laboratory that never uses cut-off levels, FTS would like to make some suggestions about how hair strand testing evidence should be instructed by the family courts:

1. Hair strand testing, in conjunction with nail testing, should be instructed as expert evidence by way of a letter of instruction or agreed questions recorded in the order. FTS can help with template letters, along with proposed standard wording for an order instructing this expert evidence.

2. The use of cut-off levels must stop. This is expert evidence that should be instructed on this basis. Interpretation of results must have regard to all relevant factors and not simply with reference to standardised cut off levels. Laboratories should always present the courts with a full picture of all findings, no matter whether they are found to be above or below a cut-off level. Testing companies must provide the legal system with a full evidential picture in order to ensure a child is not left in an unsafe living situation or removed from their parent due to misleading results.

3. Local authorities and lawyers should be better informed about how to understand and challenge disputed results that have used cut-off levels, in the same way a contested paediatric report or radiological report might be challenged in a non-accidental injury case.

4. Testing companies should factor in all legal developments on hair strand testing and stop arguing that cut-off levels are a valid method in the family courts.

In summary, forensic evidence should never be filtered before it is presented in court. When the future of a family hangs in the balance, as is often the case when hair strand tests are instructed for the family courts, forensic toxicology results must be presented in full and interpreted as accurately and with as much context and explanation as possible.

Paul Hackett has served as managing director of Forensic Testing Service (FTS) since 2024. He began his career with the Home Office Forensic Science Service (FSS). Following the successful launch of the world's first National DNA Database in 1995 Paul served on the FSS Management Team to support the expansion of the UK Police’s DNA testing and operational capacity. In the years since he’s worked across several operational and commercial roles at the FSS, Eurofins, Key Forensic Services, in addition to establishing Key Forensic Solutions Ltd.

About FTS
FTS was set up with the sole purpose of providing specialist drug, alcohol and DNA toxicology services and expert interpretation for Family Law and Child Care Proceedings

FTS offers comprehensive forensic toxicology services, providing laboratory analysis and expert opinion evidence tailored for family court cases. Our services are designed to support legal teams, social workers, and the judiciary in making informed decisions about the welfare of a child.

Our forensic lab is accredited to ISO/IEC 17025:2017 and Lab 51 (toxicology lab) standards. We are also certified by the Society of Hair Testing and the Society of Toxicological Forensic Chemistry.

To instruct FTS expert opinion and toxicology services, please contact the FTS Customer Support Team on 01924 480272 or Email This email address is being protected from spambots. You need JavaScript enabled to view it.

Website: https://www.forensic-testing.co.uk/