Friday, October 15, 2004

How to obtain specimens at post mortem for analytical toxicology

After the body death, body fluids and tissues can be rapid changes in cellular biochemistry as autolysis proceeds, and drugs and other poisons may be released from their binding sites in tissues and major organs, also unabsorbed drug may diffuse from the stomach. Special care should always be taken in the selection of blood and tissue sampling site(s), the method of collection of samples, and the labelling of sample containers.

The standard procedure for toxicological analysis performed at laboratory requires the collection of blood and urine samples. Appropriate tissue (brain, liver etc.) and stomach contents should be collected at post-mortem but will not normally be required unless special investigations are required; however they should be retained at the mortuary. Special care is required in specimen collection and storage for certain drugs and poisons e.g. alcohol, cocaine, insulin, solvents, gases and cyanide. The amount found on analysis naturally depends on the amount taken and the time between administration and death. Though the latter is usually measured in minutes, low dosage-or treatment- may allow survival for hours or even days.
In suspected cyanide poisoning it is helpful to collect specimens of blood from more than one peripheral site, and also stomach contents. In cases where the source of cyanide is not known it may be useful to obtain a small specimen of brain (~ 20 grams) from a site deep within the brain to confirm the presence of cyanide.
If there is prolonged storage of blood specimens after post-mortem, it is possible to generate significant quantities of cyanide, probably as a product of bacterial action. The use of blood specimen containers containing 2% sodium fluoride is recommended to prevent this. Blood and tissue specimens are best stored at 4oC and should be analysed as soon a possible after collection. It is important to try to identify the exact source of the cyanide taken by the deceased.

Measurement of both carbon monoxide and cyanide may be helpful in cases involving fires. However, analysis of blood specimens should be carried out without delay. In such cases there is a tendency for the carbon monoxide concentration to decrease with time and the cyanide concentration to increase. Use of blood specimen containers containing 2% sodium fluoride is advisable, particularly in "sensitive" cases or those involving multiple fatalities.
Urine (preferably at least 20 mL) should be placed in 1-2 plain 20 mL sterile plastic container(s). If only a small amount of urine is available, this should be placed in a plain 5 ml glass tube. Boric acid containers should NOT be used. Urine specimens, however small, taken at post-mortem are of great value in screening for an unknown drug or poison, particularly substances of abuse.

Blood for quantitative analysis (~ 5 mL) should be taken from two distinct peripheral sites, preferably left and right femoral veins, with care taken not to draw a large volume containing blood from more central vessels. The precise sampling site must be indicated on the label. Femoral blood can be taken by cutting the external iliac vein proximal to the inguinal ligament, and milking the distal cut into a plain 20mL sterile plastic container. Approximately 2.5mL of this blood should be placed in a second fluoride/oxalate tube containing additional sodium fluoride (equivalent to 2% wv in 2.5mL) as a preservative.
Blood for qualitative analysis (screening) An additional larger specimen of blood (~ 20mL) for qualitative screening should be taken from the heart (preferably right atrium or inferior vena cava) or if necessary from another convenient large vessel. The site of collection must be indicated on the label. Container: This specimen should be placed in a plain 20 mL sterile plastic container.

Stomach tissue and contents may be useful in the investigation of oral cyanide poisoning, or in cases of rapid death where relatively large amounts of unabsorbed drug may be found in the stomach. In cases of suspected drug overdosage the entire stomach contents should be retained. If distinct tablets or capsules are observed in the stomach contents, these should be carefully extracted, and put in individual containers (e.g. plastic urine containers). Identification of such material can be carried out by reference to a computerised database of pharmaceutical products.

Liver tissue may be useful in certain complex poisoning cases. It is usual to take a portion of the right lobe of liver since it should be uncontaminated with bile and less affected by drug diffusion from the liver; 100 grams is sufficient for most analytical purposes.
Brain, A portion of about 100g brain should be taken; this may be useful in the investigation of death due to gases or volatile substances. Measurement of brain concentration of certain drugs may be helpful in certain cases e.g. cocaine deaths. The specimen should be placed in a glass specimen jar or nylon bag (volatile substance deaths) and deep-frozen prior to transport to the laboratory.

Lung A portion of about 100g lung from the apex should be taken. This may be useful in investigation of death due to gases or volatile substances. The specimen should be placed in a glass specimen jar or nylon bag and stored at 4oC prior to transport to the Laboratory. If death was possibly caused by the inhalation of hydrogen cyanide fumes, a lung should be sent intact, sealed in a nylon ( not polyvinylchloride ) bag11.

The Laboratory should be able to provide appropriate specimen containers for the collection of blood and urine specimens at post-mortem. Suitable packaging for sending specimens by post may also be supplied if required. All specimen bottles should be clearly labelled with the full name of the deceased, date of collection, and post-mortem or reference number. In the case of blood specimens, the specific site of sampling should always be given. All specimens should be stored at 4 oC before transporting them to the laboratory. Each specimen bottle should be securely sealed to prevent leakage, and individually packaged in separate plastic bags to ensure that there is no cross-contamination. Special care is required in the storage of specimens for the analysis of insulin, alcohols, cyanide and cocaine; also for volatile liquids or gases - please contact the Laboratory for guidance. It is important to get the samples to the laboratory as soon as possible (in terms of days ) to avoid the spurious formation of cyanide in stored blood samples. This usually occurs at room temperature so, if there is to be delay, refrigeration is essential. In contrast, some positive samples may actually decrease on storage, as described by Curry. Up to 70 per cent of the cyanide content may be lost after some weeks, from reaction with tissue components and conversion to thiocyanate11.
If cyanide victim death which have occurred in hospital, the hospital pathology laboratory should be contacted as soon as possible to see if any ante mortem specimens of urine, blood, serum, or plasma are available, and these should also be sent for analysis.

The usual blood, stomach contents, urine and any vomit should be submitted to the laboratory, taking particular care that the samples present no hazardto those packing, transporting or unpacking them. The labortory should be warned in advice that a possible cyanide case is coming their way.


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