Specimen collection and analysis
In cases of suspected poisoning admitted to hospital, specimens of blood and, where possible, urine should be taken. When blood specimens are received in the laboratory and analyses are not required immediately, it is useful to separate off plasma or serum from red cells, prior to deep freezing. However, for toxins that have a significant distribution into the redcells (e.g. lead, cadmium, mercury and cyanide), it is essential to conserve samples of anticoagulated whole blood. In postmortem examinations it is important to undertake a more systematic specimen collection and great care is required in the selection of sampling sites, method of collection and use of appropriate specimen containers. Where an industrial accident has occurred there may be access to ‘scene residues or materials used in a chemical process. Analysis of these materials can yield valuable clues when the precise nature of the chemical agent is unknown. However, prior to transportation to the laboratory, separate packaging from any biological specimens is advisable to avoid the risk of contamination.
Vomit, stomach aspirate and washout fluid are now rarely available from cases of acute poisoning admitted to hospital. Stomach washout procedures (except in rare cases) have been replaced by the administration of oral activated charcoal in most developed countries. In fatal cases, the whole stomach and its contents can be removed at postmortem examination. When dealing with the initial examination of stomach contents, or vomitus, it is helpful to note any unusual smell, colour or other appearance, such as the presence of fresh or altered blood (e.g. vomit with the appearance of ground coffee indicates bleeding in the upper gastrointestinal tract). Great care should be taken when dealing with cases that involve the oral ingestion of cyanide salts, as the contents of the stomach may represent a serious hazard and risk of secondary poisoning (a fume cupboard, or safety cabinet, must be used in these circumstances). Earlier techniques used to examine stomach contents, such as isolation of poisons by dialysis or steam distillation, are now obsolete, particularly since the development of more sensitive and specific analytical techniques. Venous blood should be collected in all cases of suspected poisoning; for metallic poisons and anions, such as cyanide, a potassium ethylenedi aminetetraacetic acid (K-EDTA) container is the most appropriate. A wide range of blood collection tubes are available commercially; to avoid the possibility of contamination, the use of products certified as suitable for trace-element analyses is strongly recommended, particularly when dealing with environmental or subclinical exposure to agents such as lead, cadmium and aluminium. Blood-collection tubes that contain gel separation barriers should not be used. When blood specimens are received in the laboratory in an unusual container, it may be useful to request a ‘blank’ container that can be analysed for the presence of any contaminating substance. It is equally important to ensure that reliable blood-specimen containers are used for postmortem examinations. These can be supplied to the pathologist ahead of any postmortem examination as part of standard specimen-collection kits.
An early specimen of urine with no preservatives added should be collected, with care taken to ensure that the sample is not contaminated during the collection process. If patients are undergoing chelation therapy it can be useful to collect sequential 24-hour urine specimens into acid-washed plastic urine containers. Hair analysis for trace elements has often been used for diagnostic purposes in cases where an individual complains of symptoms for which no cause can be found by routine medical or pathological investigations. However, experience and published studies show that the results can be misleading (Taylor 1986; Seidel et al. 2001). Hair analysis has more application in surveys of population exposure and in investigations of suspicious deaths, such as those that involve arsenic or mercury. The long persistence of metals in hair samples compared to their relatively short duration in blood or urine specimens is a major advantage in this context. Analysis of hair sections can also yield a chronological record of when doses were administered. Specimens such as tissues, skin and bone may sometimes be collected at postmortem examination as part of the investigation of complex medicolegal cases.
Lung tissue should be collected from post mortem examination in cases of beryllium related deaths as this is a target organ for this element. All those involved in selecting and submit ting samples for analysis should consider the possibility of metals and anions being present so that suitable samples, packaging and storage are employed at the start. This is particularly important for volatile substances, where attention should be paid to ensuring that loss due to volatilisation from the sample or sorption into sample containers is minimised. Similarly, for metals and anions, precautions must be taken to prevent contamination with these substances. Some types of sample containers can leach metallic elements (e.g. somegel- containing blood tubes may be contaminated with barium) and solutions added to prevent microbial growth may contain metals and/or anions if they are not prepared from standards and solvents (including water) of suitable purity. Glass containers should never be used to collect specimens for aluminium analysis.
