When tissues are sampled they should be collected quickly and placed immediately into airtight containers. This is particularly important if volatiles or inhalants are suspected. Liver, kidney, brain, lung and spleen are the most frequently collected postmortem tissues.
Liver is a particularly important organ because of the very large number of drugs that undergo hepatic metabolism and the fairly extensive published reference data that exist. To reduce the possibility of drug diffusion from the small bowel, tissue from deep within the right lobe is preferred (Drummer 2004). The concentrations of drugs and metabolites in liver are often elevated, hence this specimen has limited interpretive value. However, liver is particularly useful for highly protein-bound drugs and the comparison of liver/blood drug ratios may allow the differentiation of acute overdose from chronic drug use for some drugs.
Most drugs pass through the kidney as a result of urinary elimination. Kidney is an important specimen in cases of suspected heavy-metal poisoning owing to accumulation in this tissue. The presence of heavy metals orethylene glycol during toxicological tests maybe accompanied by structural changes to the kidney that can be documented using histological tests.
Spleen is an important specimen for cyanide or carbon monoxide analyses, particularly in fire-related deaths where blood may be compromised or unavailable. Lung and brain are valuable specimens in cases involving volatiles or inhalants.
Brain tissue is lipid rich and has a tendency to concentrate some drugs, particularly lipophilic analytes, narcotics and halogenated hydrocarbons (Skopp 2004). If quantitative drug brain concentrations are used, it is important to know the location of the specimen because the brain is a non-homogeneous matrix. Drug concentrations within the brain may vary several-fold from one region to another owing to its complex structure and differing composition. Brain is not widely used in routine toxicological analysis.
Muscle is not routinely encountered, despite the fact that it frequently contains relatively high drug concentrations, particularly for substances with high volumes of distribution. Perfusion rates between sites and drug concentrations are not consistent, and drug concentrations must be interpreted accordingly. Muscle is encountered more frequently for ethanol determination in the absence of blood, or during the investigation of a suspected injection site.
Hair has been used in a variety of antemortem toxicology settings to provide a history of drug exposure and has therefore found applications in workplace drug testing, in monitoring of persons on probation or on parole for drug use, in insurance testing to verify the truthfulness of statements made by applicants relating to whether they use drugs or are smokers,in childen dangerment, in drug-facilitated sexual assault and in other types of criminal casework (Nakahara 1999; Kintz et al. 2006; Curtis, Greenberg 2008). One of the major advantages is the long drug detection window compared with many other specimens. Hair may allow drug exposure over several weeks or months to be determined, depending on the length of the hair.
Segmenting the hair by length may allow an approximate timeline for exposure to be determined based on head hair growth rates of approximately 1 cm per month (Clauwaert et al. 2000). Hair should be cut as close as possible to the scalp from the posterior vertex region of the head, since this region shows least variation in growth rate.Typically a lock of hair equivalent to the thickness of a pen or pencil is collected.
The colour, length, sampling site and any obvious cosmetic treatment of the hair should be recorded. The root (proximal) and tip (distal) sections of the hair should be clearly identified. Although head hair is the preferred specimen, hair from other sites (e.g. pubis, axillae) may be used, but interpretation of analytical findings may be more complex. The lock of hair is typically tied, wrapped in aluminium foil and stored under dry conditions in the dark at room temperature. Hair is also a useful specimen in postmortem investigations where arsenic or heavy metals are suspected. Although postmortem hair analysis is not yet widespread, there is growing interest because it may provide valuable interpretive information pertaining to the chronological sequence of toxin exposure (Cirimele et al. 2002).
Hair has also proved to be useful in cases where exhumation is necessary (Tsatsakis et al. 2001). If hair is collected post mortem, it should be sampled at the very beginning of the examination to reduce the risk of contamination. Hair can provide complementary toxicological information. Issues with drug testing in hair include external contamination, ethnicity and pigmentation, chemical treatment and the use of appropriate cut-off concentrations. Contamination of the hair with drugs from other sources (external deposition, environmental contamination, sweat or sebum) is generally minimised by pretreatment of the sample using a variety of aqueous and organic rinses or wash steps prior to analysis.
Other keratinised specimens such as nails can also be used to determine long-term exposure to drugs or poisons, in particular heavy metals such as thallium, arsenic or lead. However,drugs are deposited into nails at a much slower rate. External decontamination procedures should be performed prior to analysis.