Fundamentals of Analytical Toxicology. Robin Whelpton
2016). Blood and bile concentrations are generally poorly correlated (Ferner & Aronson, 2018). At autopsy, bile can usually be collected by syringe aspiration from the gallbladder, or by incision-compression if the bile is too viscous. In the event of cholecystectomy, sampling can be performed directly in the common bile duct. The site of sampling should be recorded. Care should be taken to avoid contamination of the specimen by stomach or intestinal contents.
2.3.15 Other tissues
Other tissue samples may be useful when investigating deaths where volatile substances such as solvents or gases are implicated. Brain, subcutaneous fat, lung (apex), spleen, and kidney are the most useful; 10–20 g wet weight of unpreserved tissue should be collected into separate containers. The specimen should be placed in a specimen jar or nylon bag (VSA- or anaesthetic-related deaths), taking care not to overfill sample containers, and stored at –20 °C or below prior to and during transport to the laboratory.
Measurement of brain concentrations of certain poisons may be useful in specific instances, for example such measurements are said to be helpful when investigating possible cocaine-related deaths. Spleen is rich in erythrocytes and hence may provide a valuable alternative specimen in which to measure carboxyhaemoglobin saturation if blood is not available (Vreman et al., 2006).
2.3.16 Insect larvae
Analysis of blowfly (Calliphora vicina) and other insect larvae that feed on rotting flesh may facilitate detection of many drugs originally present in human or animal tissues, although quantitative extrapolations are unreliable (Introna et al., 2001; Tracqui et al., 2004; da Silva et al., 2017). Pupae may be preserved for years, but drug and metabolite concentrations in post-feeding and pupating larvae are much lower than in feeding larvae, suggesting that the larvae metabolize and eliminate drugs during development. Metabolism of nordazepam to oxazepam by blowfly larvae has been observed (Pien et al., 2004).
2.3.17 Keratinaceous tissues (hair and nail)
Hair and nail may be useful for detecting exposure to poisons that may have been eliminated from other commonly sampled fluids and tissues before the hair sample was collected (Section 18.5). Hair may also survive longer after burial than other tissues. If a single exposure to a poison is suspected, as in drug-facilitated sexual assault (DFSA, date rape), but the suspected agent is not detected in blood or urine, waiting for 1–2 months for head hair to grow and then performing segmental analysis may reveal the presence of the drug (head hair on average grows at the rate of 1 cm per month).
Head hair (a bunch of hairs the thickness of a pencil, ca. 100–200 hairs) should be either plucked in the case of a deceased person, or tied at the root end with cotton thread and then cut ca. 2 mm from the scalp at the vertex posterior (crown) of the head (Box 2.3; Figure 2.2), making sure the scissors are level with the scalp and not at an angle. Tying with thread helps preserve the alignment necessary for segmental analysis. The sample should be laid aligned in aluminium foil, with the proximal end clearly identified. Pubic or axillary hair may be substituted if no head hair remains, or if the head hair has been excessively bleached or permed, which tends to destroy sequestered drug, but the ability to perform segmental analysis is lost.
Box 2.3 Protocol for collection of head hair for testing for drug exposure
The ideal sample is collected from the vertex (the crown) of the head by cutting approximately 2 mm from the scalp
Take a sample of hair about the thickness of a pencil (100–200 hairs)
Pinch the hair tightly with the fingers and tie with cotton thread at the root end before cutting
Cut the sample as close as possible to the scalp, making sure the scissors are level with the scalp
Still holding the sample tightly, align the cut root ends of the sample and carefully place flat on a piece of aluminium foil with the cut root ends projecting about 15 mm beyond the end of the foil
Mark the root end of the foil and fold the foil around the hair and pinch tightly to keep in place
Fold the foil again in half lengthwise
Place the sample in a tamper-proof envelope. Complete and sign the request form, making sure that the donor also signs if necessary. If there are special instructions that do not appear on the form, but are felt relevant, make a note on a separate sheet and enclose with the sample
Nail clippings may be used to monitor uptake of antifungal drugs such as itraconazole and terbinafine (Leyden, 1998). In post-mortem work, whole nails should be lifted from the fingers or toes. This provides an even longer potential window for detecting exposure than hair. However, relatively little is known about the mechanisms of uptake and retention or drugs and metabolites in nail. In addition, the slower growth rate of nail, especially toe nail, as compared to hair makes segmental analysis, and hence interpretation of quantitative results, virtually impossible (Krumbiegel et al., 2016; Solimini et al., 2017).
Figure 2.2 Schematic of head hair collection
2.3.18 Bone
Bone marrow aspirate may be useful in the identification of certain poisons in exhumations, for example, where all soft tissue has degenerated (Orfanidis et al., 2018). As with synovial fluid and pericardial fluid, bone marrow is normally within a relatively protected environment, and thus may also provide a valuable sample for drug screening or for corroborative ethanol measurement, for example, in the event that other samples are not available (Maeda et al., 2006; Cartiser et al., 2011; Tominaga et al., 2013). Analysis of bone itself may be useful if chronic poisoning by arsenic or lead, for example, is suspected.
2.3.19 Injection sites
Possible injection sites should be excised, packaged individually and labelled with the site of origin. Appropriate ‘control’ material (i.e. from a site thought to not be an injection site) of similar composition should be supplied separately.
2.3.20 Scene residues
Such material, which may include tablets, powders, syringes, infusion fluids, infusion lines, bandages, foodstuffs, drinks, and so forth, may give valuable information as to the poison(s) involved in an incident, and should be packaged separately from any biological samples. This is especially important if volatile compounds are involved. If police attend a scene these materials may find their way to a forensic laboratory rather than accompanying the patient.
All items should be labelled and packed with care. Scene residues may be particularly valuable when investigating deaths that may involve medical, dental, veterinary, or nursing personnel, who may have access to agents that are difficult to detect once they have entered the body, and in deaths that have occurred in hospital. Investigation of deaths occurring during or shortly after anaesthesia should include the analysis of the anaesthetic(s) used, including inhalational anaesthetics, in order to exclude an administration error. Needles must be packaged within a suitable shield to minimize the risk of injury to laboratory and other staff.