Drug Testing - The Process
Specialist Sample Analysis
Drugs, chemicals, and biological substances when ingested accumulate and are stored in keratinized matrices, such as hair and nails. In recent year drugs analysis within keratinized matrices has received considerable attention over traditional drug testing methodologies employing body fluids, such as urine or serum due to several advantages. The ability to determine patterns of substance/drug misuse being at the forefront.
Numerous studies indicate that head hair grows at an average rate of 1cm a month, therefore for every 1cm length of hair we can go back 1 month in time establishing a historical pattern of misuse. However should the substance misuser be unable to provide a sample of head hair for whatever reason, we can also test body hair, but due to a differentiation between the lag and growth phases we cannot give a specific month by month breakdown.
When a sample of hair is analysed for drug use, it is first washed to remove dirt and any external drug deposits, then stripped of melanin. The first stage analysis, known as screening is performed by Enzyme Linked Immuno Sorbant Assay (Elisa) that detects not only traces of drugs but their metabolites; these are chemicals that appear only when the body has converted the drug.
If a positive result appears than a second stage process known as a confirmation test is performed and the sample results are confirmed by gas chromatography/mass spectrometry (GC/MS). This second test has a cutoff level to eliminate specimens containing drug levels that could arise from environmental exposure. To be considered positive a sample must show the presence of the drug in these two different assays. This two step analysis protects against false positive reports.
Governmental View
The parliamentary Office of Science and Technology states in a report published on Hair Drug Testing in the UK: ‘Gas chromatography-mass spectrometry (GS-MS) is considered by the Forensic Science Service the gold standard in hair testing. It is usually the only test which is accepted in the Courts, GC-MS is the tool of choice because it has good sensitivity, selectivity, specificity, a high degree of standardization, sample throughput, and instrument ruggedness’
(Post note 28, 2004).
