Hair strand tests for drugs and alcohol have become central to Family Court proceedings, and are carried out by government-approved commercial laboratories.
They work on the principle that when a drug passes into the bloodstream, it leaves traces within a person’s hair. As the hair grows, it retains the traces and also provides a timeline of when the drug was taken.
To carry out the test, a sample of hair is cut into 1cm (0.4in) segments – the approximate length a hair grows in one month. The hair closest to the scalp will cover the most recent month, the next centimetre the next month, and so on.
The segments are broken up or mixed with solvents before being put through a chromatography process.
Results are then measured against the ‘cut-off’ level, which labs used to distinguish between active drug use and passive exposure. However, some in the legal community think it is too simplistic a measure to rely on.
Although it wasn’t significant in Emily’s case, some types of hair are more absorbent than others, and this can cause major problems, according to experienced family barrister Sarah Branson.
She recalls representing a young baby’s father whose hair strand testing came back positive for crack cocaine – something that “didn’t fit with the picture of the rest of his life”.
She says the father was already caring for an older daughter, with no concerns from social services, and he had no history of using the drug.
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