Monitoring of drugs of abuse and medicaments in hair and nails - applications and pitfalls in forensic toxicology

The analysis of keratinized matrices, such as hair and nails, has achieved considerable importance in forensic toxicology as drug intake or drug exposure can be detected for a much broader time frame than in classical specimens, such as blood and urine. Head hair can serve as a chronological record of consumption with a growth rate of 0.6 to 1.4 cm per month [1]. Hair analysis is applied on a regular basis for the retrospective long-term monitoring of drugs, drugs of abuse and alcohol consumption behaviour or for abstinence control in the process of regranting driver’s license [1]. Pitfalls of hair analysis are contamination of the specimen by dust/smoke from the environment as it was reported for drugs of abuse such as cocaine, cannabis, and heroin [2-4]. Therefore, it is important to distinguish contamination of a hair sample from drug intake or from exposure to the drug. Bias in analysis results can also occur because of hair colour; it was demonstrated that incorporation of basic drugs into hair is increasing with higher melanin content in hair [1, 5]. The lack of a suitable hair sample because of cosmetic treatment or the removal of all head and body hair constitutes another pitfall. In such cases, nails may be an alternative matrix to hair but the application of nail analysis still has to be evaluated. Several drugs of abuse (e.g. cocaine, amphetamines, opiates, and tetrahydrocannabinol), drugs (e.g. benzodiazepines, antidepressants) and the alcohol marker ethyl glucuronide have already been detected in fingernails or toenails, respectively [6-11]. Unlike hair, nails grow continuously throughout one’s life [12]. Growth rates of fingernails range from 1.9 to 4.4 mm per month with an average of 3 mm per month [13]. Toenails grow slower with an average of 1.6 mm per month [14]. The nail is formed at the germinal nail matrix and nail bed which are well supplied by blood from digital arteries [15]. Hence, these compartments constitute regions of drug incorporation into the nail plate. Although melanocytes are located in the germinal nail matrix and nail bed, the nail plate lacks melanin granules under healthy conditions [16].