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Encyclopedia of Physical Science and Technology EN016H-959 August 1, 2001 11:6

Toxicology in Forensic Science 909

VIII. REPORTS X. ARTEFACTS IN ANALYSIS

Once an analysis is complete a report must be issued to A. Stability of Drugs
the client(s) which accurately details the analytical find-
Chemical instability occurs for a number of drugs and
ings. These results should indicate the type of tests con-
metabolitesthatwillaltertheconcentrationandevencause
ducted, the analytical method used (HPLC, GC–MS, etc.),
the drug to disappear if storage conditions are not optimal.
on which specimens the analyses were conducted, and of
This will occur at room temperature and even sometimes
course the result(s). The result(s) should be unambiguous,
◦
when specimens are stored frozen at −20 C.
using such terms as “detected” or “not detected.” The use
Alcohol will be lost to evaporation unless sealed tubes
of the term “not present” should be avoided, as it implies
are used or specimens are stored at −80 C; however, al-
◦
no possibility of the substance being present. A toxicolo-
cohol can also be produced by bacterial action on glucose
gist can rarely be so definitive and can only indicate that a
and other sugars found in blood. The use of potassium
substance was not detected at a certain threshold concen-
fluoride as a preservative (minimum 1% w/v) is required
tration. For this reason, a detection limit alongside tests for
to prevent bacterial activity for up to one month after col-
specific substances should be provided for “not detected”
lection when the sample is stored at 4 C.
◦
results.
For quantitative results consistency in units is advised
and should not be given with more significant digits than B. Bioconversion
the accuracy will allow. For example, there is no point
A number of drugs can undergo chemical changes in
in reporting a result for blood morphine as 0.162 mg/L
a body after death. These chemical changes can be ei-
when the accuracy and precision of the method is ±20%.
ther metabolically mediated or caused by spontaneous
A result of 0.16 mg/L would suffice.
degradative processes. For example, the metabolism of
For drug-screening results, it is advisable to provide
heroin to morphine occurs in life, in blood and other tis-
clients with an indication of the range of substances a
sues following collection, or even in situ when a person
method is capable of detecting and some indication of the
has died. For this reason, heroin or the immediate 6-acetyl
detection limit, such as “at least therapeutic concentra-
tions” or “only supra-therapeutic concentrations.” morphine are rarely detected in blood. Morphine is there-
In postmortem cases, all reports should indicate the fore the target drug. Aspirin is also converted rapidly to
site of blood sampling and provide (where relevant) some salicylate by hydrolytic mechanisms.Most drugs activated
comment on the possibility of postmortem artefacts such by de-esterification or hydrolysis will be subject to similar
as redistribution. By incorporating these comments, those processes.
reading the report are less likely to unwittingly misinter- Nitro-containing drugs, such as the benzodiazepines,
pret the results. nitrazepam, or flunitrazepam, are also rapidly biotrans-
formed after death to their respective amino metabolites
by the action of certain types of bacteria. Toxicologists
IX. INTERPRETATION OF must therefore target their analyses to these transforma-
TOXICOLOGICAL RESULTS tion products rather than the parent drug.
Sulfur-containing drugs, such as dothiepin, thiopental,
Interpretation of any toxicological result is complex. Con- or thioridazine, are also subject to bacterial attack during
sideration must be given to the circumstances of the case, the postmortem interval, leading to progressive losses over
and in particular what significance may be drawn from the time. Of course, the parallel process of tissue loss will also
toxicology. For example, the finding of a drug in poten- affect the tissue concentration during putrefaction.
tially toxic concentrations in a person killed by a gun-
shot wound to the head cannot reasonably lead to the C. Redistribution
conclusion that the drug caused the death. On the other
hand, the absence of an obvious anatomical cause of Theprocessofdeathimpartsanumberofotherspecialpro-
death will lead investigators to consider the role of any cesses that affect the collection and analysis of specimens
drug use. Considerations must include the chronicity of obtained at autopsy. These include postmortem redistri-
drug use, the likely time of ingestion, the route of inges- bution in which the concentration of a drug in blood has
tion, the age and health of the person (e.g., presence of been affected by diffusion of drug from neighboring tissue
heart, liver, or kidney disease), the use of other active sub- sites and organs such as stomach contents. This is mini-
stances,andevengeneticfactorsthatmayleadtoanaltered mized, but not arrested, by using peripheral blood from
metabolism. the femoral region. Even liver concentrations are affected