Examqo › Examqo library › Forensic medicine › Sudden death and toxicology · IMLE
Forensic toxicology — specimen selection and postmortem interpretation
Interpreting a drug concentration in a body depends on where and when the sample was taken: peripheral blood from the femoral vein reflects the concentration at death better than heart blood, because after death drugs move from organs into nearby vessels (postmortem redistribution).
Why it matters in the exam
The exam asks which sample suits which question. Femoral blood is the main sample for quantification; heart blood is used for screening only, because its concentrations can be artificially high for drugs with a large volume of distribution such as tricyclic antidepressants and digoxin. Vitreous humour is protected from contamination and decomposition and is used for alcohol, electrolytes and assessing glucose and ketones — high vitreous glucose supports hyperglycaemia before death, but low glucose does not prove hypoglycaemia because glucose falls after death.
Urine reflects exposure in recent days, not effect at the moment of death. Stomach contents help identify ingestion of a large amount. Liver is useful when there is no blood. Hair shows use over months and, when cut in segments, the timing of use. In death from insulin injection, the supporting finding is a high insulin level with low C-peptide in serum, and sometimes tissue from the injection site, because exogenous insulin is not accompanied by C-peptide.
Preservation decides whether the result will be reliable: tubes with sodium fluoride inhibit bacterial alcohol production and cocaine breakdown, and refrigeration or freezing slows degradation. Some substances are unstable — cocaine breaks down to benzoylecgonine — so the metabolites are reported too. Every sample is labelled, sealed and recorded in the chain of custody. Embalming and decomposition disturb results, so sampling is done early.
Key points
- Femoral blood for quantification; heart blood for screening only.
- Postmortem redistribution raises concentrations in central blood.
- Vitreous: alcohol, electrolytes and high glucose.
- High insulin with low C-peptide supports injection.
- Sodium fluoride, refrigeration and chain of custody.
Summary table
| Sample | Main use | Strength | Limitation |
|---|---|---|---|
| Femoral blood | Quantification and link to effect | Less postmortem redistribution | Limited volume |
| Heart blood | Screening | Large volume | Artificially high concentrations |
| Vitreous humour | Alcohol, electrolytes, glucose | Protected from contamination and decay | Glucose falls after death |
| Urine | Exposure in recent days | High concentrations, good screening | Does not reflect effect at death |
| Hair | Use over months | Timeline by segments | Not for acute exposure |
In the full version for subscribers
- A simple algorithm
- Memory aid
- Exam traps
- 5 review cards
- Enough for IMLE
The full version is open to subscribers of: Forensic medicine, Diagnostic pathology, Medical licensing exam (IMLE).
Subscriber? Read the full topic Plans and prices 25 free questions
Sources
- Society of Forensic Toxicologists / American Academy of Forensic Sciences: Forensic Toxicology Laboratory Guidelines, 2006 — Specimen collection
- Clarke's Analysis of Drugs and Poisons, 4th edition (2011) — Postmortem toxicology: specimen selection and interpretation
- Knight's Forensic Pathology, 4th edition (2016) — Toxicological aspects
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.