Forensic Toxicology

• Forensic toxicology is usually required in cases of suspicious or sudden deaths, criminal investigations, drug-facilitated sexual assault (DFSA), road traffic incidents, and animal deaths/poisonings.
• In cases of suspicious or sudden deaths, the deceased may have been prescribed drugs and there may be evidence at the scene.
• In criminal investigations, both the deceased/victim and suspect may be analysed to determine state of mind or to determine if the suspect was under the influence of drugs.
• In cases of DFSA, the victim's blood and/or urine are analysed.
• In road traffic incidents, the driver and/or passengers may be analysed, as the passenger may have distracted the driver.
• The primary requirement for forensic toxicology is sufficient case background information, drug history, and specimens.
• UK forensic toxicology relates to road traffic casework or “complex” casework such as DFSA, assaults, and deaths.
• Various types of reports, Courts, and considerations in providing evidence and application of that evidence are factors in forensic toxicology.
• Analysis and interpretation of forensic toxicology results needs to be appropriate to the case.
• Forensic toxicology is largely based on practitioner experience.
• Investigative considerations will impact on the interpretation of forensic toxicology results.
• In animal deaths/poisonings, the deceased animal is analysed by a veterinarian or the RSPCA.
• Toxicology investigations are usually required in cases of suspicious or sudden deaths, criminal investigations, drug-facilitated sexual assault (DFSA), road traffic incidents, and animal deaths/poisonings.
• A toxicology report should clearly present the findings and meaning of the results, including the techniques used, units of measurement, additional analytical notes, and results listed per sample.
• Interpretative comments in a toxicology report should be clear and concise but substantial enough to present sufficient meaning of the findings.
• GHB is produced endogenously in the body, not exogenously, and its production is not affected by the presence of other compounds.
• An expert witness toxicology report should clearly present the case background/circumstances and instructions received, expert content, range and qualification as to opinion, literature relied upon, and conclusions.
• If presenting toxicology “results” the content is more typical written style often in sections responding to certain questions or “instructions”.
• The extent and content of toxicology reports varies between organisations and individuals but the wording should be clear and appropriate to the results and the initial request, and presented in a suitable toxicology report.
• A toxicology report should be signed by reporting scientist(s) and peer reviewed where necessary.
• Paracetamol toxicity can result in liver necrosis and may not always be associated with a high paracetamol concentration in the blood due to latent toxicity.
• A toxicology report should be formatted to comply with the provisions of s9 Criminal Justice Act 1967 (called a “section 9” report/statement).
• The toxicologist should be keeping up with published work and case experience can provide relevant comments based on the laboratory findings.
• The findings and the report should also be considered in conjunction with any inter-dependent results such as post-mortem examination findings in deaths.
• Given all the factors involved, not least the many physiological aspects of an individual themselves, “does a fatal or non-fatal range for drugs actually exist?”
• The sample type must also be taken into account, as well as AM vs PM, potential difference in concentrations in blood versus plasma and water content.
• Case experience very important to enable a collation of knowledge of the results of many different drugs across many different case types and scenarios
• Fatal range = typical concentration associated with death
• The presence or absence of drugs could be related to the limit of detection or limit of quantitation of the analytical technique – was this appropriate for the drug and question posed?
• In deaths, this is further complicated by the issue of PM redistribution
• The toxicologist also relies on published data but these can be skewed towards unusual cases which may involve abnormally high concentrations or cases with other interesting features.
• At 19:00, the blood ethanol concentration could have been between 126 and 186 mg/dL, with a most likely concentration of 158 mg/dL.
• Results in fatalities involving alternative causes of death (e.g. hanging, shooting, road traffic accident) are useful for comparison with the results of other post-mortem cases where drugs ingestion has been implicated.
• In criminal investigations, a blood sample may indicate an individual’s drug status at the time of arrest but urine results would be better to cover the last 1-3 days if appropriate.
• Clinical trial or in life data may be available to provide some evidence of “normal” concentrations but invariably do not relate to the exact dosage or route of administration in a particular case.
• The time coverage for different sample types (e.g. blood, urine) should be considered in terms of the relevance of the toxicology findings.
• The absence of a drug may indicate non-compliance with the prescription regimen.
• Non-fatal range = concentration achieved in cases of survival
• In post-mortem cases, liver, urine, bile, etc may represent previous use rather than very recent use.
• Evidence of drug use, empty packets of medication, a glass with tablet residue or unusual liquid, and a syringe still present in the arm of a user can provide indications of recent ingestion.