Fundamentals of Analytical Toxicology. Robin Whelpton

the likely cause, and estimated time, of ingestion/death and the nature and quantity of any substance(s) implicated

       If the patient has been treated in hospital, a summary of the relevant hospital notes should be supplied to include details of emergency treatment and drugs given, including drugs given incidentally during investigative procedures

       Note of occupation/hobbies

       A copy of any preliminary pathology report, if available

      

       2.3.1 Sample collection and preservation

      In general biological specimens should ideally be stored at 2–8 °C before transport to the laboratory. Exceptions to this include hair, nail, and filter-paper adsorbed DBS. Dried blood stains and other dried forensic specimens may of course be handled similarly (Schütz et al., 2002).

Each specimen bottle should be securely sealed to prevent leakage, and individually packaged in separate plastic bags. Particular attention should be paid to the packaging of samples to be transported by either post, or courier in order to comply with current health and safety regulations. Sample volumes or amounts smaller than those indicated in Tables 2.4 and 2.5 are often sufficient to complete the analyses required. Submission of very small samples may, however, result in reduced sensitivity and scope of the analyses undertaken, but nevertheless such samples should always be forwarded to the laboratory. Any residual specimen should be kept at –20 °C or below until investigation of the incident has been concluded.

In post-mortem work, the use of disposable hard plastic (polystyrene) tubes is recommended. If these are not available, then containers with secure closures appropriate to the specimen volumes should be used. Some laboratories provide specimen containers for collecting post-mortem blood and urine specimens. It may be important to note if urine was obtained by use of a catheter. Suitable packaging for sending specimens by post may also be supplied. When death has occurred in hospital and poisoning is suspected, any residual ante-mortem specimens should be obtained as a matter of urgency from the hospital pathology laboratory (not only chemical pathology and haematology, but also immunology, transfusion medicine, and virology departments may be a source of such specimens) and submitted for toxicological analysis in addition to post-mortem specimens. Recording the date and time of collection of such samples is important. Note that the availability of ante- or peri-mortem specimens does NOT negate the need to collect post-mortem specimens.

      All organ and tissue samples, and any tablet bottles or scene residues, should be placed in separate containers to avoid any chance of cross-contamination. Sampling through tissues containing high concentrations of an analyte may lead to contamination of the sample. On the other hand, toxicological analysis of samples from an embalmed body, formalin-fixed specimens, or even on tissue from microscope slides may be requested. Clearly, concentrations of any drugs or metabolites that survive in such specimens are likely to have been altered by the embalming or fixation process. Formaldehyde is highly reactive, and the identification and the evaluation of possible analyte degradation products and/or formaldehyde derivatives may be helpful (Nikolaou et al., 2013; Takayasu, 2013; Ameline et al., 2019).

      Sample integrity is of prime concern if there are medico-legal implications because evidence may have to be produced in court. Precautions to ensure sample integrity include: (i) proper sample labelling, (ii) use of tamper-proof containers, (iii) collection of samples such as hair, nail, and femoral blood before opening the body and documenting the fact, and (iv) proper accompanying documentation (chain-of-custody documents). Samples collected for clinical purposes (or even for the coroner) are often not of ‘evidential’ quality, but such samples may be all that is available. DNA testing may be used to establish the origin of certain samples if there is concern over sample integrity.

      

       2.3.2 Blood

      In analytical toxicology, plasma or serum is normally used for quantitative assays, but some poisons such as carbon monoxide, cyanide and many other volatile organic compounds, lead and other toxic metals, and some drugs such as chlortalidone, are found primarily in or associated with erythrocytes. Thus, haemolyzed whole blood should be used for such measurements. The space above the blood in the tube (‘headspace’) should be minimized if carbon monoxide, solvents, or other volatiles are suspected.

Provided that the samples have been collected and stored correctly, there are usually no significant differences in the concentrations of poisons between plasma and serum. However, if a compound is not present to any extent within erythrocytes then using lysed whole blood will result in an approximately two-fold dilution of the specimen. A heparinized or EDTA whole blood sample will give either whole blood, or plasma as appropriate. The immunosuppressive drugs ciclosporin, everolimus, sirolimus, and tacrolimus are special cases because redistribution between plasma and erythrocytes begins once the sample has been collected and so the use of haemolyzed whole blood is indicated for the measurement of these compounds.

      In addition to the obvious alteration in sample volume, careful interpretation of results is needed if solutions containing ascorbic acid (risk of loss of acid labile compounds, reduction of metabolites), sodium metabisulfite (reduction of metabolites), or sodium azide (interference in immunoassays) are added to specimens.

       2.3.2.1 Collection of blood post-mortem

      In order to maximize the reliability of measurements performed in post-mortem blood, it is recommended that (i) the interval between death and the post-mortem examination is minimized, (ii) the body/samples are stored at 2–8 °C before the examination/after collection, (iii) that blood is collected from two distinct peripheral site(s), preferably the femoral vein(s), after tying off the vein proximally to the site of sampling (Lemaire et al., 2016), and (iv) a preservative (approximately 2 % w/v, fluoride) is added to a portion of the blood sample/the sample from one vein. The exact site of blood sampling should be recorded, as should the time of sampling and (approximate) time of death if known.

      If sufficient sample is obtained, this should be divided between unpreserved and preserved (fluoride) tubes, otherwise the entire sample should be preserved unless there is a possibility of poisoning with fluoride or compounds giving rise to fluoride in vivo such as fluoroacetate. Added fluoride may also enhance decomposition of organophosphorus compounds (Moriya et al., 1999). If only heart or cavity blood is available this should be clearly stated.

      Post-mortem blood (ca. 20 mL) for qualitative analysis only should be taken from the heart (preferably right atrium), inferior vena cava, or another convenient large vessel. The precise sampling site must be recorded on the sample tube. The blood should be free-flowing.

      

       2.3.3 Urine

      The presence of metabolites may sometimes assist identification of a poison if chromatographic techniques are used, but not all poisons appear in urine as either parent compound, or metabolites. A 50 mL specimen from an adult, collected in a sealed, sterile container, is sufficient for most purposes. No preservative should be added. The sample should be obtained as soon as poisoning is suspected, ideally before any drug therapy has been initiated. However, some drugs, such as the tricyclic antidepressants (amitriptyline, imipramine, etc.), cause urinary retention, and a very early specimen may contain insignificant amounts of drug. Conversely, little poison may remain in specimens taken many hours or days after exposure even though the patient may be very ill, for example as in acute paracetamol poisoning.

High concentrations of some drugs or metabolites can impart characteristic colours to urine (Table