Clinical applications of hair testing for drugs of abuse — the Canadian experience

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Abstract

During the last 2 decades there has been a substantial increase in illicit drug consumption in North America. It has been repeatedly shown that the personal history of drug use is far from being accurate. Fearing legal consequences and embarrassment of admitted illicit substance use, most users tend to deny or, to under-report illicit drug consumption. These facts have stressed an urgent need for a biological marker which does not lose its sensitivity within a few days after the end of exposure and which may yield a cumulative reflection of long term exposure to illicit drugs. Hair analysis has emerged as such a marker. A variety of illicit and medicinal compounds have been shown to be incorporated into hair including trace metals, barbiturates, amphetamines, opiates, phencyclidine, cocaine, nicotine and cannabis. Hair analysis for drugs of abuse provides long-term information on an individual’s drug use; its window of detection is limited only by the length of the hair and typically, ranges from a week to several months. After establishing and validating several hair tests during the last decade, we have analyzed over 1000 hair samples for different drugs of abuse. We used RIA for screening and GC–MS for confirmation of positive results. The aim of this report is to illustrate the diagnostic usefulness of hair testing in different age groups (newborns, children, adults) and circumstances: (criminal cases, athletes, child custody cases, etc.).

Introduction

During the last 2 decades there has been a substantial increase in illicit drug consumption in North America. One of the most frequently used drugs is cocaine. In many large American cities, the prevalence of cocaine use reaches 45% of the adult population [1]. Statistics collected by the Addiction Research Foundation (ARF) in Toronto show that in the late 1980s 10% of the Ontario population between the ages of 18 and 28 have at some point during the last year consumed cocaine; [2] all indicators are pointing to an increase in this percentage in the 1990s. Parallel to the decrease in the cost of crack cocaine, there has been an increasing number of cocaine related crimes and deaths.

While cannabis and cocaine are more commonly used illicit substances, heroin, morphine, amphetamines, benzodiazepines and phencyclidine are also consumed by large numbers of individuals [3], [4], [5].

It has been repeatedly shown [6], [7], that personal history of drug use is far from being accurate. Fearing legal consequences and being embarrassed to admit illicit substance use, most users tend to deny or, to under-report illicit drug consumption.

The validity of blood and urine tests is dependent on the elimination half-life of the compound in question. In case of cocaine, which has a very short elimination half life of <1 h, the drug and its metabolites are not likely to be detected for more than a few days in either blood or urine [8]. Other drugs, (e.g., cannabis), have longer elimination half-lives, however, even these drugs can be detected only for a maximum of 3–4 weeks after use [9].

Consequently, urine testing will only provide a reliable answer for short term recent exposure; it is also not unusual to tamper with urine samples to achieve false negative results [10].

These facts have stressed an urgent need for a biological marker which does not lose its sensitivity within a few days after the end of exposure and which may yield a cumulative reflection of long term exposure to illicit drugs.

During the last few decades, hair analysis has emerged as such a marker. A variety of illicit and medicinal compounds have been shown to be incorporated into hair including trace metals, barbiturates, amphetamines, opiates, phencyclidine, cocaine, nicotine and cannabis [11].

Hair analysis for drugs of abuse provides long-term information on an individual’s drug use; its window of detection is limited only by the length of the hair and typically, ranges from a week to several months. In this respect, hair analysis is complimentary to urinalysis, and their combination is capable of providing information about the short- and long-term drug use of an individual.

While the fact that each hair follicle is supplied by an artery is well established, the mechanisms leading to the absorption of xenobiotics into the growing hair shaft have not been well elucidated [12]. The fact that hair grows continuously at an average rate of 1 cm/month offers a potential time dimension to the accumulation of drugs and their metabolites in the shaft [13]. At present, hair analysis is increasingly used as a tool for the detection of drug exposure in utero, passive exposure of children in homes where parents actively use drugs, in criminal cases, in the workplace, in child custody cases, and in detoxification clinics.

The aim of this report is to illustrate the diagnostic usefulness of hair testing in different age groups and circumstances.

Section snippets

Methods

After establishing and validating several hair tests during the last decade, we have analyzed over 1000 hair samples for different drugs of abuse. Most of the samples were analyzed for cocaine and its metabolite — benzoylecgonine.

The hair was not washed prior to testing, unless external contamination was suspected. If washing of the hair sample was included in the procedure it was performed according to a methodology well established in our laboratory [14].

Following the washing, the sample was

In utero drug exposure

  • 1.

    A preterm baby which was born at 35 weeks gestation weighed 1888 g. The mother admitted to morphine addiction 4 years earlier and marijuana use prior to this pregnancy, but denied drug use during pregnancy. The infant’s urine tested negative for cocaine but positive for benzodiazepines. We received the baby’s hair which was collected 3 weeks after birth and tested it for cocaine, morphine and benzodiazepines. The hair was positive for cocaine and benzodiazepines and negative for morphine.

Discussion

In addition to the indications exemplified above, there are other areas in which hair testing may prove extremely useful. For instance, testing of inmates suspected of or known to use drugs or monitoring the parole population. At the moment, the preferred method in jails for drug screening is urinalysis; however, it is a well known fact that inmates can evade drug testing by buying ‘clean’ urine — a common practice in jails.

Finally, one of the potentially most important applications of hair

Conclusions

From the examples listed above and from the increase in the number of requests coming to our laboratory, it is evident that hair testing is emerging as a reliable biological marker for cumulative and temporal account of exposure to illicit substances. None of the routinely used biological matrices including blood, urine and saliva can provide information to the same extent as hair. Given the current level of understanding, hair testing can provide singularly important information in so many

Acknowledgements

This work was supported by grants from the Medical Research Council of Canada, and The Motherisk Research Fund.

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