Guest post by Dr. Michael Robertson – Independent Forensic Consulting
Dr. Robertson is a forensic toxicologist at Independent Forensic Consulting and a specialist consultant to a range of medico-legal organisations. Dr. Robertson graduated with a Doctor of Philosophy in Forensic Medicine from Monash University with a background in pharmacology, toxicology and analytical chemistry. Dr. Robertson is an expert in drug and alcohol-related matters and has assigned, supervised, performed and certified hundreds of toxicological analyses and has testified as an Expert Witness in most courts within Australia for prosecution, defence and plaintiff lawyers. He holds membership of The Australian and New Zealand Forensic Science Society (ANZFSS); The International Association of Forensic Toxicologists (TIAFT); the Society of Forensic Toxicologists (SOFT) and The Forensic and Clinical Toxicology Association of Australia (FACTA). He has been a member of the SOFT Drugs and Driving Committee and the SOFT Drug Facilitated Sexual Assault Committee and also serves as an invited reviewer for the international journal, Forensic Science International.
In understanding the process of drug tests, lawyers are better equipped to utilise the results more effectively in defending drug charges.
What do the results of drug tests actually tell us? Following is some further information about drug tests that you may find useful:
Screening (Immunoassay or IA)
- Only looks for some drugs and only at concentrations above the cut-off;
- May lead to positive results for unrelated drugs;
- A ‘negative’ result does not mean no drug is there i.e. may have been below the cut-off;
- A ‘positive’ result does not confirm the presence of the drug, only that it ‘may’ be present.
Confirmation (GC-MS; LC-MS)
- Generally by mass-spectrometry (GC-MS or LC-MS);
- Specific and able to differentiate between similar drugs e.g. Duromine vs. ‘Speed’;
- Positive if drug above the administrative cut-off;
- Negative or not detected if below the cut-off;
- Negative does not mean none present, only that it is not above the cut-off;
- Often only report those drugs listed in AS4308:2008 i.e. other drugs may be seen and not reported as present.
- Generally only administrative i.e. lab can detect drugs below the cut-off;
- A ‘not detected’ result may not mean no drug is there; simply it is not there above the cut-off.
- Blood results represent drug use in previous hours or days;
- Drug levels represent those present at the time of collection not necessarily time of interest;
- Urine levels represent drug used in the previous hours, days or weeks;
- No correlation can be made between results and impairment, only the drug has been consumed and may lead to impairment (see previous newsletter to help establish impairment);
- Many drugs will be not be seen or detected by routine drug screens – ensure you understand what was looked for and more importantly what was not looked for;
These are guidelines and are intended to assist you in understanding results of drug tests. If you are uncertain how to interpret results or not sure what the lab results are telling you, if you find that the results do not make sense or are not what you expect, you should contact someone who can fully explain the results i.e. what was found and importantly what the testing would not have found even if present.
Q. Does the presence of low levels of THC mean the individual was impaired at the time of the accident?
A. The simply presence of THC does not indicate impairment and needs to be corroborated with other evidence of impairment.
Q. Could an individual charged with Supply have 11g of methamphetamine for personal use?
A. Yes – There is no common dose or user pattern for illicit drug users but rather doses vary based on the desired effect of the user, the size of the user, the purity of the drug and experience of the user. These variables make it difficult to generalise when estimating a number of dosage units in order to determine if any amount of drug, within reason, is likely to be used by an individual for personal use or for other purposes i.e. supply.
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