Forensic toxicology is based on examining specimens for the presence of drug(s). These can be drugs suspected of being used in a case (targeted testing), or a broad series of tests aimed at covering a large range of common substances. These substances generally include alcohol, drugs of abuse (eg amphetamines, benzodiazepines, cannabis, cocaine, opioids) and a range of common legally obtained drugs.1. In practice, the drugs detected are often not suspected from the given circumstances. Hence a broad drug screen should be conducted for most of the common drugs, rather than conduct analyses for one or a limited range of drugs.
In cases of a suspected poisoning the usual practice is for toxicologists to conduct a broad drug screen to cover the drug groups listed above as well as to target drugs or chemicals suspected of being consumed. This latter information may come from an examination of the scene, or information provided by known associates and family members. In some cases, the constellation of symptoms presented by the subject may yield a clue as to the possible poison. Reports should clearly indicate the drug(s) detected and the methods used to detect drugs. In some situations drugs or drug metabolites are detected, but are not confirmed. These results should be flagged as presumptive, or unconfirmed, meaning a real possibility exists that this substance is present, but that the identification does not meet accepted standards of reporting. This may occur because of limited availability of specimen, lack of a suitable analytical method, or the drug detected may not be considered an important finding from a forensic point-of-view.
Except for occasional situations referred to above, it is accepted practice only to report a drug when the laboratory has complete confidence in its presence in that specimen. In other words, the drug finding is confirmed. Reporting a drug as “indicated” or “not confirmed” means the laboratory cannot be sure the substance is necessarily present in the sample. If the result were to have some significance in the case then the laboratory must endeavour to confirm the presence, otherwise the result has no evidentiary value. Many forensic laboratories are now subject to peer review through quality assurance programs and have regular formal inspections as part of the accreditation or certification requirements. These processes regulate the performance of laboratories and are aimed at continuous improvements in the quality of the service. These requirements apply particularly to Australian forensic laboratories. Furthermore, it is a requirement that methods to detect drugs in forensic exhibits are fully validated and are fit for the intended purpose. Laboratories are expected to have data to verify that the method is fit for the intended purpose.