Low Down

  There are several ways of obtaining blood samples at autopsy and perhaps the most useful advice is what not to take. Blood should never be obtained from body cavities after evisceration, as it is almost certain to be contaminated with other body substances. The practice of scooping 'blood' - or more accurately, bloody fluid - from the paravertebral gutters or the pelvis is always unacceptable, as urine, intestinal contents, gastric contents, lymph, pleural and ascitic fluid and general tissue ooze will always find their way into such a sample and negate the reliability of analysis. When a large [1] haemothorax or [2] hemopericardium is pre- sent, it may be grudgingly acceptable to use such blood or clot, if a clean sample is taken immediately on opening the chest, before any dissection or disturbance of organs is made. This is only second best to obtaining intravascular blood - and, in the case of alcohol and other diffusible substances, the results cannot be relied upon, as ...

It is obvious that the shorter the delay between death and the removal of samples, the better. Though some toxic sub- stances, such as carbon monoxide, form stable compounds in the body, many others (especially volatile substances and some pharmaceutical products) will be broken down by post-mortem autolysis and decomposition. When an autopsy cannot be performed quickly after death, in terms of a few hours, then mortuary refrigeration is the first line of defence to slow up putrefactive and autolytic processes. If delay is foreseen, usually because of administrative problems in obtaining consent or authority for autopsy, it may be possible to obtain a sample of blood through the body surface, such as puncturing the femoral vein by needle and syringe. The blood can then be kept in optimal conditions, with preservative where needed, and perhaps with the serum or plasma separated from the cells to avoid haemolysis. Similarly, urine could be drawn off by catheter or even suprapubic punctur...