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Specimen types , Blood

المؤلف:  Sue Jickells , Adam Negrusz (Editors)

المصدر:  Clarkes Analytical Forensic Toxicology

الجزء والصفحة:  194

2026-10-10

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Specimen types

Blood

In living patients the dose of a drug is most closely correlated with its concentration in blood or plasma. Blood has therefore been used as one of the primary specimens in postmortem toxicology. In most cases postmortem blood is relatively fluid and typically has numerous small clots. Sampling can usually be achieved with a syringe and large-gauge needle. It used to be assumed that postmortem blood was more or less homogeneous in terms of where in the body it is sampled. It is not. Postmortem blood concentrations of many drugs may vary from site to site (see later) due to a process known as postmortem redistribution. As a result, much attention has been focused on the site of collection of postmortem blood samples. A word of caution may be appropriate about specimen labelling. Samples simply labelled ‘blood’ may have been collected from almost anywhere in the body. Even samples labelled as ‘heart’ blood may not have been collected from the heart itself, but drawn blind through the chest wall, and may include pleural or chest fluid, pericardial fluid and even gastric contents if the death was traumatic. On occasion, it might be collected outside the body following a traumatic accident, as pooled blood in a body bag. As the awareness of postmortem redistribution grows, great faith is being placed in the analysis of subclavian and femoral blood compared with cardiac blood. However, the toxicologist should be wary of the anatomic purity of these specimens when large volumes are supplied, and should take this into account when offering an interpretation. Unless the femoral or subclavian veins are ligated, it is very likely that some blood will be drawn from other vessels. For example, a skilled pathologist or technician can sometimes draw as much as 50 mL blood from the femoral vein. However, the femoral vein is relatively small and it is highly likely that much of that volume will be drawn down from the larger iliac vein and inferior vena cava. It is difficult to collect more than 5–10 mL from a ligated femoral vein unless the leg is massaged.