Hair analysis was initially used in the 1960s and 1970s to evaluate exposure to toxic heavy metals through the use of atomic absorption spectroscopy. At the time, it was not possible to examine hair for drugs because the methods weren't sensitive enough. Years later, the use of radioimmunoassay allowed for the detection of certain organic drugs in hair. Today, gas chromatography coupled with mass spectrometry is the method of choice and is routinely used to document drug exposure in forensic science. One major advantage of hair testing compared to blood or urine testing is that it has a larger window (weeks to months versus 2 to 4 days) and is therefore able to provide a long-term history of an individual's drug use. Hair samples are typically taken from the scalp, although it has been suggested that other locations, such as arm hair, pubic hair, or axillary hair, could be used for alternative sources of drug detection when scalp hair is not available. While it has been suggested, various studies have found significant differences in drug concentrations between scalp hair and these alternative sources. These differences are believed to be caused by better blood circulation, a greater number of apocrine glands, and a different growth rate.
The mechanism by which the chemicals are bound to hair is not exactly known, although several suggestions have emerged. It was suggested that diffusion enhanced by drug binding to intracellular components of hair cells such as the hair pigment melanin could be a cause. However, this would not be the only mechanism as, when tested, drugs are trapped into the hair of albino animals, which lack melanin. Another proposed mechanism was the possibility of the drug binding with certain sulphydryl-containing amino acids and diffusing into the hair cells. The abundance of amino acids such as cysteine form cross-linking disulfide bonds, which would bind the drugs. Various studies have also demonstrated that when given the same dosage, black hair tends to incorporate a greater amount of the drugs when compared to blond hair. This gives rise to discussions about a possible genetic variability of drug disposition in hair.
Of course, much more research is required before all questions surrounding hair drug testing can be satisfied, but it seems that hair analysis for the identification of drug use is quickly gaining recognition. Hair analysis could be a very useful tool to use in conjunction with conventional drug testing in toxicology.
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ReplyDeleteI remember hearing on some documentary once about how much information about where we have been and what we have been around can be contained in the molecules in our hair. It is crazy how long things like drug particles can remain hair and be used as a viable method of drug testing. Also, it is interesting that darker hair seems to bind more drug molecules than lighter hair. It will be interesting as more research is done into the exact mechanisms by which these phenomenon occur.
ReplyDeleteVery interesting blog! I've always wondered what kinds of methods were used for hair analysis. Because it is a relatively newer field, it leaves one wondering about whether there is any possibility of these instruments giving off false positives when analyzing hair, however.
ReplyDeletePlease always remember to cite your sources.
ReplyDeleteThis is actually very interesting! I think there are many advances being done in forensics that it is fascinating to keep up with. It makes me wonder what else could be analyzed through our hair.
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