Hair Testing for Drugs of Abuse
The following article has been provided by Dr Tom Bassindale, Member of the Royal Society of Chemistry, The International Association of Forensic Toxicologists and the Society of Hair Testing (twitter @tombasso)
Hair Testing for Drugs of Abuse
Of all the common biological matrices for drug testing, hair samples can give us the longest window of detection. Once a drug is incorporated into the hair it remains locked in place until that hair is either cut or falls from the head. This window can be months or in long hair multiple years. The growth rate of one centimetre per month for head hair is used. The centimetre nearest the root is the most recent growth and shows the last month of drug use history.
There are thought to be three main methods of drug incorporation into hair:
- Directly into the hair as it grows. Hair follicles are a rich source of blood, supplying the required nutrients for hair to grow.
- Through sweat and sebum (drugs in blood are excreted into sweat and sebum, an oily substance secreted by sebaceous glands). Hair is porous and can absorb liquids.
- Finally environmental contamination. If a person is in a smokey environment around cannabis or methamphetamine users for example, it may be possible for that drug to be in contact with the hair. It could also be possible for powders or liquids to be spilled onto the hair.
A schematic of these methods is shown below:
A sample is usually collected from the back of the head and ideally would be around 3-4 mm diameter. Other body hair can be used. The analysis of samples will usually involve the following steps:
Washing – to remove as much as possible any external contaminants present. Most commonly an organic solvent (methanol, hexane, acetonitrile) is applied to the hair for a short period of time and removed. Other approaches include water, buffers or shampooing. These washes are analysed for evidence of external contamination (2).
Extracting drugs from hair - Many approaches are used for this also, commonly soaking for longer periods in methanol, acid (for example HCl), alkali (NaOH) or a buffer.
Clean up – the extraction is not specific to drugs, a subsequent clean up step may be used to remove unwanted compounds (eg. solid phase or liquid liquid extractions).
Analysis – this may be immunoassay (for screening) followed by mass spectrometry (MS) confirmation of positive results (LC-MS/MS or GC-MS), or directly to a MS.
As technologies have developed assays have become more sensitive and less mass of sample is required. Multiple classes of drugs can be analysed in a single extract of 10-50 mg of hair. Most types of drugs frequently abused have been detected in hair.
The Society of Hair Testing has published guidelines for labs (3). The suggested values for MS detection levels are summarized in the table below:
|Drug Class||Limit of Quantitation|
|Opiates(e.g. morphine, codeine)||<0.2 ng/mg|
|Amphetamines(eg. MDMA, amphetamine)||<0.2 ng/mg|
|CannabinoidsTHCTHC-Acid||<0.1 ng/mg<0.2 pg/mg|
|CocaineCocaine metabolites||<0.5 ng/mg<0.05 ng/mg|
Hair testing has been applied to many legal scenarios – drug facilitated sexual assault; driving license applications (in some countries); family court (child access); workplace drug testing; therapeutic drug monitoring; doping in sports and recently in evaluating exposure of children living in houses used to manufacture methamphetamine (4).
P. Kintz, Value of hair analysis in postmortem toxicology, Forensic Sci. Int. 142 (2004) 127–134
L. Tsanaclis, J.F. Wicks, Differentiation between drug use and environmental contamination when testing for drugs in hair, Forensic Sci. Int. 176 (2008) 19-22.
Society of Hair Testing, Recommendations for hair testing in forensic cases, Forensic Sci. Int. 145 (2004) 83-4.
T. Bassindale, Forensic Science International. 10.1016/j.forsciint.2012.01.003T. Bassindale, Quantitative analysis of methamphetamine in hair of children removed from clandestine laboratories – Evidence of passive exposure? Forensic Sci. Int. (2012), doi:10.1016/j.forsciint.2012.01.003