Hair strand testing of parents (and other family members) is relatively common in family court cases, especially care proceedings. Most judges, and social work and legal professionals working in this field are therefore used to reading the now lengthy reports that are produced by drug testing companies, setting out and analysing the results. Over the years these reports have become increasingly lengthy due to the increasing amount of standard explanatory “blurb” that needs to accompany the bare result to assist with interpretation and in understanding the proper limits on the testing science. There is an evaluative element to hair strand testing, particularly in cases of suspected excessive alcohol use, and it is important to be aware on what the science is and is not capable of telling us and how probative an apparently positive result really is.

In a recent case Lextox reported as follows (the Family Court has given permission for this extract to be published in anonymised form).

Q : The donor of these results has afro-caribbean hair. Is the growth rate of this type [of] hair slower than other types of hair? Would slow growth of this particular type of hair affect the time it would take to show a negative result or have any other impact on the tests results?

When assigning time periods, Lextox use an average growth rate of 1 cm per month as per the guidance from the Society of Hair Testing (SoHT). However it is an average growth rate meaning that in some people hair can grow at faster or slower rates (With a distribution generally between 0.6cm – 1.4cm per month). In addition, the time periods calculated assume that the hair was cut as close to the scalp and as straight to the scalp as possible. Due to the very curly nature of Afro Caribbean hair, this can make cutting the sample close to the scalp difficult. Therefore the time periods are quoted as approximate and should not be over-interpreted.

It is my understanding that Afro Caribbean hair grows at a slower rate than Caucasian hair. A 1 cm section of Afro Caribbean hair may therefore cover longer than the assigned 1 month time period. If [the subject’s] hair has a slower than average hair growth rate then the levels detected would be unaffected however the time covered by the hair analysed would be longer.

It is possible for a donor to provide a positive hair test result for approximately 3-4 months following cessation. This is because with Caucasians approximately 85% of scalp hair is growing at any one time, with the remaining approximate 15% in the resting (non-growing) phase. When an individual has regularly used a drug for example cannabis, stops and continues to abstain from using the drug it usually takes approximately 3-4 months for a person to return a “Not Detected” result. This is because the resting phase of the hair usually last [sic] 3-4 months. As the resting phase consists of only approximately 15% of the hair the levels detected are expected to be at “low levels”. A large decrease would be expected after the first month once an individual stops using cannabis followed by smaller decreases until a “Not Detected” is obtained after 3-4 months.

It is also my understanding that Afro Caribbean hair can have a higher percentage of hair in the resting (non-growing) phases. If this was the case, although it may not take longer to see a not detected result, the decrease in levels may not be as large as seen with Caucasians.

The usual blurb that this firm uses is as follows (I’ve not included all of it, just the bits that seem relevant to this issue):

Normal hair growth is a cycle composed of three stages, active growing (Anagen phase), transition (catagen phase) and a resting stage (telogen phase). There are significant differences in the relative proportions of actively growing hair and resting hair between different areas on the body. Scalp hair has been selected as a test specimen as it grows at a reasonably constant rate, ranging from between approximately 0.6-1.4cm per month with a population average of 1cm per month, and approximately 85% is actively growing (Pragst & Balikova, 2006) (Harkey, 1993).

…the time periods are approximate and calculated with the following assumptions :

• The donor has a growth rate of 1cm per month
• That the hair sample was cut as close to the scalp as possible
• That the hair sample was cut straight with the scalp

A variation in any factors detailed above will affect the approximate time period calculated. …it can take approximately 2 weeks for hair to have sufficiently grown above the scalp to be available for inclusion within a cut hair sample…

When an individual stops taking a drug, it is still possible for low levels of drugs to be detected in a hair sample. This is due to the fact that at any one time approximately 15% of the hair is not actively growing. This hair would contain drugs that would have entered the hair during the period of drug use (Tsanaclis, 2007).

I asked for the extracted information above to be published because it seemed to me to be that although we all know (and are told in the blurb) that there are many caveats, assumptions and limitations to the interpreted results we receive, it is very easy to forget about the need to consider how the information contained in the report matches or jars with the other evidence in the case, before drawing conclusions. The extract highlights the fact that for a parent of Afro Caribbean extraction, there is a greater risk that the assumptions relied upon could lead to the court concluding that the subject has been untruthful about the date of cessation of drug use in circumstances where that was not warranted. There is of course a risk of this in all cases, because all hair growth rate assumptions are based upon an average, but the risk is by definition greater for those who are part of a subset of the population whose hair tends to grow more slowly, is more difficult to cut and test, and which has a tendency to have a higher proportion of hairs in the resting phase. It’s just a risk, but it is not one that is likely to have been actively considered in the absence of any warning in the blurb materials.

I asked Lextox about this extract and whether or not they were aware of any research papers specifically covering the differences between Caucasian and Afro Caribbean hair, and whether they were considering expanding or altering their general blurb to highlight the differences in hair behaviour and characteristics between different ethnicities. They have sent me this response, from which it appears that they consider their general blurb to be sufficient. They did not point me in the direction of any research studies, indeed they did not answer that particular question.

The use of hair testing in family courts is a well-established science in use across the UK in thousands of family law and child care cases annually. Lextox’s expertise lies in the detection of drugs, metabolites and alcohol markers in hair using highly specific and sensitive instrumentation accredited by the United Kingdom Accreditation Service (UKAS). Lextox experts are also members of the Society of Hair Testing (SoHT), an independent international body which provides guidance on appropriate analysis techniques for the detection of drugs, metabolites and alcohol markers in hair. By complying with the SoHT consensus, Lextox therefore provides hair analysis within internationally agreed recommendations.

Among those operating within these guidelines, it is well known that there are a number of assumptions when it comes to hair testing, particularly regarding the time period covered by the hair analysed. It is not possible to determine the exact growth rate of hair on a case by case basis for each individual donor. Therefore, a common assumption regarding hair growth rates is required for use in all cases in order to apply an approximate time period to the specific hair section analysed – this being that scalp hair grows at a reasonably constant rate, ranging from between approximately 0.6 – 1.4 cm per month, with a population average of 1cm per month.  

As such, when assigning time periods to a sample, Lextox uses an average growth rate of 1cm per month as per the guidance of the SoHT to calculate all time periods reported. The SoHT does not recommend that hair types from alternative ethnic backgrounds are treated any differently, although it is also documented generally that scalp hair from donors of Afro-Caribbean descent may grow more slowly, sometimes as slow as 0.5 cm per month. In our opinion this does not differ sufficiently enough from the extreme ranges of Caucasian hair growth rate to have any significant effect on the testing procedures involved, and as such Lextox applies the guidance from the SoHT to calculate all time periods reported. This practice is standard within the industry.

With regards to the percentage of hair in the resting phase, again this cannot be determined on an individual basis, and can only ever be an assumption. As such, Lextox uses the percentages of growing and non-growing hair derived from scientifically published data to help in the interpretation of the analysis results.

In summary, Lextox assesses each hair sample submitted on an individual, case by case basis. Any hair sample that is deemed too curly to section into the requested sections, whether of Afro Caribbean descent or not, will not otherwise be sectioned and this information will be relayed back to the client with a number of options on how best to proceed with that particular sample. In such a case, the assessment is made purely in consideration of the physical nature of the sample submitted, as sometimes the hair is manageable by our suitably trained laboratory technicians to handle and accurately align, measure and section.  

In all cases if a client has specific questions on the analysis results, including those regarding growth rates and the growth cycle of hair, Lextox also considers these on a case by case basis and in doing so responds to all client and court related enquiries free of charge.

This statement (which I’ve quoted in full) refers to the Society of Hair Testing, of which Lextox are said to be members. I’ve no reason to doubt that, but unfortunately the SoHT website does not publish its members, which is surprising. And nor is there anything on their website which helps to illuminate matters. There is no mention of ethnicity or of different hair types in any of the material I can find on that site.

The “consensus” document referred to is on the site, and dates from 2004. It includes the simple line “In general, head hair is estimated to grow at approximately 1.0 cm per month.” But otherwise nothing much of relevance to this issue. Read in context it appears this was originally agreed by the members of the society as long ago as 1997.

There is a 2011 “statement” which appears to be good practice guidelines. It includes this passage :

It is accepted that head hair grows at an average rate of 1 cm each month [12] and a sample cut from the posterior Vertex region of the head, close to the scalp is preferred as this region of the scalp is associated with least Variation in growth rates. The amount of hair required for analysis is a “lock of hair” or a pencil thickness of hair. It is important to collect sufficient hair in order to carry out routine tests and to allow for a repeat analysis or confirmation test by a second laboratory.

Concerns are often raised in relation to leaving a visible “bald patch” of particular concern with small children or individuals with baldness or thinning hair. In these cases, collection of several smaller hair samples from multiple Sites, focusing where possible around the posterior Vertex region is acceptable.

Head hair is the preferred sample, however, if head hair is not available alternative collection sites should be considered including pubic, underarm and beard hair. Collection of intimate samples requires consideration for the privacy of the donor while ensuring that the integrity of the collection process is not compromised. Growth rates and dormancy characteristics of hair from these alternate sites, differs from head hair.

The reference [12] is to a 1993 paper : M.R. Harkey, Anatomy and physiology of hair, Forensic Sci. Int. 63 (1993) 9-18, (a time when hair strand testing was emergent, as far as I understand it – indeed the SoHT was founded in 1995).

None of the references to research papers that I can find on the SoHT OR appended to the standard blurb in Lextox reports appear superficially (i.e. based on their title) to relate to the issue of different characteristics of hair taken from particular ethnic groups.

I do not presently have the capacity to track down, pay for and read all of those references, or indeed to search for those not listed – so I may be wrong about this – but it is not entirely clear that there is very much good research about this issue at all, and I wonder (it is no more than that at present) whether when it is said that “it is also documented generally that scalp hair from donors of Afro-Caribbean descent may grow more slowly, sometimes as slow as 0.5 cm per month”, this may mean that this is anecdotally a known issue, but nobody has yet bothered to do any robust research on it.

When I have a moment I will send a copy of this blog post to the SoHT and ask them if there is anything relevant, and will update if and when any response is received.

If anybody has had cause to explore this issue or read the relevant papers in one of their cases I would be grateful for any further light that you can shed on this. I doubt in reality that I will have time to do much follow up any time soon given other commitments.

Feature Photo : lab stuff courtesy of iTc on Flickr – thanks!