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Specimen types , Antemortem specimens

المؤلف:  Sue Jickells , Adam Negrusz (Editors)

المصدر:  Clarkes Analytical Forensic Toxicology

الجزء والصفحة:  198

2026-10-12

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Specimen types

Antemortem specimens

 Not infrequently, victims of an accident or over dose may be admitted to hospital, albeit sometimes surviving only briefly, before they die. When that occurs, it is common for blood and sometimes urine and gastric contents to be collected as part of the medical evaluation and treatment. There are at least two reasons why collection and analysis of antemortem specimens can be invaluable, even if death occurs fairly soon after admission to hospital. Firstly, analysis of hospital admission specimens gives a good idea of the circulating blood concentration at the time of admission to the hospital, which by definition is unaffected by postmortem redistribution, and may provide the only reliable indicator of dosage. Secondly, the antemortem specimen may provide the sole opportunity to perform meaningful toxicology if the person survives long enough for alcohol or drugs to be cleared from the body prior to death, or to be diminished to a concentration of limited or no forensic value. Even if blood or plasma collected on admission is not available, clearly timed specimens drawn several hours later may still be useful if allowance is made for clearance and for the presence of drugs administered as part of treatment. There are some caveats. Blood collected for clinical purposes is usually centrifuged to separate serum or plasma for testing on clinical analy sers. However, once separated, the serum or plasma may not be resealed after analysis. This will allow ethanol and other volatile substances such as solvents to evaporate and this possibility should be taken into account if the sample is analysed subsequently for forensic purposes, sometimes several days later. Another problem that can occur with clinical samples is the deterioration of some drugs in unpreserved serum, most notably cocaine. Intuitively, a serum or plasma specimen collected in the casualty or emergency department might be expected to contain higher concentrations of unchanged cocaine than a postmortem blood sample collected later. However, this is often not the case, because postmortem blood is often collected in tubes containing sodium fluoride which inhibits cocaine hydrolysis, whereas clinical samples are typically unpreserved.