Applications
Comparison with urine testing
There are essentially three types of problem with urine drug testing:
• false-positives when not confirmed with GC-MS
• embarrassment associated with observed urine collection
• evasive manoeuvres, including adulteration.
These problems can be greatly mitigated or eliminated through hair analysis. It is usually possible to obtain a fresh, identical hair sample if there is any claim of a specimen mix-up or breach in the chain of custody. If the fresh hair sample can be collected, this would make hair analysis advantageous compared to urinalysis, since an identical urine specimen cannot be obtained at a later date. Another potential use of hair analysis is to verify accidental or unintentional ingestion of drink or food that has been laced with drugs. For a single use, the hair will not test positive. For example, the ingestion of poppy seeds appears to be sufficient to create a positive urine result, while the ingestion of up to 30 g of poppy seeds does not result in a positive hair identification (Sachs, personal communication, 1994). In toxicological investigation of crimes facilitated with gamma-hydroxybutyrate (including drug-facilitated sexual assault) when the report of the event was delayed, a segmented analysis of hair was shown to be very successful (Goulle et al. 2003; Kintz et al. 2003, 2004). The most important use of hair analysis, however, may be in identifying false-negatives, since neither abstaining from a drug for a few days nor trying to ‘beat the test’ by diluting urine alters the concentration in hair. Urine does not indicate the frequency of drug intake in subjects who might deliberately abstain for several days before drug screenings. While the analysis of urine specimens cannot distinguish between chronic use or single exposure, hair analysis offers the potential to make this distinction. Table 6.2 illustrates the differences between hair and urine.
General disadvantages of hair testing versus urine testing include: low concentrations of drugs particularly for marijuana requiring high confirmation sophistication, interpretation issues such as use versus exposure, hair colour and racial bias, and ease of adulteration. It also needs to be made clear that hair analysis is not useful for immediate detection of recent drug intake.
