POSTMORTEM TOXICOLOGY

BY BETHOD JUMANNE

MANAGER,

FORENSIC SCIENCE SERVICES

Specimens and other exhibits

The specimens available for analysis in postmortem cases may be numerous, or limited to blood or a single tissue, depending on the case history and preferences of the submitter.

In a relatively recent death, blood, vitreous humor, at least one organ tissue (usually liver) and the gastric contents are collected commonly.

Specimens and other exhibits cont…

However, in a severely decomposed case found outdoors, muscle, hair and bone may be the only specimens available.

Proper collection and preservation of postmortem specimens is critical, since there is usually no opportunity to go back for re–collection of specimens at a later date as the body may well have been cremated or buried.

Blood

In living patients the dose of a drug is most closely correlated with its concentration in blood or plasma. Therefore, historically, blood has been used as one of the primary specimens in postmortem toxicology.

In most cases postmortem blood is relatively fluid and typically has numerous small clots. Sampling can usually be achieved with a syringe and large–gauge needle.

Urine

Urine is a useful fluid for toxicology testing, as it comprises more than 99% water and contains relatively few endogenous substances that interfere with chromatography or immunoassay tests.

However, there are three disadvantages with urine in postmortem work.

Firstly, urine is only available in about 50% of deaths, as it is fairly common for the bladder to be voided during the dying process.

Urine cont…

Firstly, urine is only available in about 50% of deaths, as it is fairly common for the bladder to be voided during the dying process. Secondly, many drugs are metabolized so extensively that the parent drug is not detected in urine, or is present only at a relatively low concentration

Urine cont…

Secondly, many drugs are metabolized so extensively that the parent drug is not detected in urine, or is present only at a relatively low concentration

The third disadvantage of urine is that urinary concentrations of most drugs are difficult, if not impossible, to interpret. The correlation between the concentration of drugs in urine and blood is extremely poor.

Urine cont…

The primary reason for this is that urine is not a circulating fluid, but is a waste product collected in the bladder. The concentrations of drugs and metabolites in urine therefore depend on the time of urine formation relative to sampling and drug ingestion.

Liver

liver is the most important. The main reasons are the large amount of tissue available, ease of collection and relative ease of sample preparation compared to other tissues.

Concentrations of many basic drugs are also higher in the liver compared to blood, making detection easier.

Liver cont…

liver is an extremely valuable tissue for the analysis of drugs that undergo postmortem redistribution because concentrations in the liver are relatively stable after death.

The only major disadvantage of the liver as a specimen is that it tends to be fatty and can putrefy faster than blood. It is therefore important that analytical methods incorporate some type of cleanup step, and are robust enough to minimise the matrix effect of the tissue.

Liver cont…

It is therefore important that analytical methods incorporate some type of cleanup step, and are robust enough to minimize the matrix effect of the tissue.

Stomach contents

Stomach (or gastric) contents are valuable for two primary reasons. After overdosage, drug concentrations in the stomach may be quite high, even after the majority of the drug has passed into the small intestine.

Analysis of the stomach contents is uncomplicated by metabolism, so drugs that are metabolised extensively in the body may be detected unchanged.

Stomach contents cont…

Similarly, drugs that may be difficult to detect in the blood because of extensive distribution in the body might be detected readily in the stomach

The disadvantage of stomach contents is its composition, which varies from a thin watery fluid to a semi–solid, depending on the amount and type of food present.

Other fluids, tissues and organs

Bile: Has been collected historically, although its usefulness is limited. Previously, bile was valuable because it contains high concentrations of drug conjugates, most notably morphine.

Bile, like urine, is a waste fluid and, with the possible exception of ethanol, the correlation between blood and bile concentrations of drugs is generally poor.

Brain, kidney and spleen

Have been used to determine and interpret the concentrations of drugs or other toxins.

The brain offers the additional advantage that it is a relatively isolated organ and should be unaffected by trauma to the abdomen and chest, although concentrations of many drugs vary considerably from one region of the brain to another.

Brain, kidney and spleen cont…

Drug concentrations in the kidney and spleen have little intrinsic significance, other than as part of the overall assessment of the body burden of a toxin, although the kidney has been found to be useful in determining heavy metal concentrations.

Brain, kidney and spleen cont…

Spleen has been used as a secondary specimen for toxins, such as carbon monoxide and cyanide, which bind to haemoglobin.

Injection sites

Forensic folklore indicates that injection sites may be valuable for determining whether or not someone has been injected with a drug or poison

Subcutaneous injection sites offer a better chance of detection, since absorption is considerably slower.

Nasal swabs

Some pathologists collect intranasal samples using cotton–tipped swabs in an attempt to demonstrate nasal administration.

However, the same principles apply as those for proving a drug was injected at a particular site and interpretation should be undertaken with caution.

Nasal swabs cont…

Using cocaine as an example, if the drug is used, one would expect to find small amounts of cocaine, and certainly cocaine metabolites such as benzoylecgonine, in the nasal passage, just through normal secretions.

Syringes and other items

Detection of some drugs, and particularly non–drug poisons, may be considerably easier in items found at the scene than through analysis of blood alone, and might also assist interpretation of the results.

For example, residues of partially dissolved medications found in a drinking glass at a scene of death can be a strong indicator of suicidal intent.

Syringes and other items cont…

Other containers used to mix poisons prior to suicidal consumption (or homicidal administration) can also be useful to the toxicologist.

Some pesticides are not detected readily in blood using routine screening procedures, but can be detected much more easily in the concentrated residue in a container.

Antemortem specimens

Victims of an accident or overdose may be admitted to hospital, albeit sometimes surviving only briefly, before they die.

It is common for blood and sometimes urine and gastric contents to be collected as part of the medical evaluation and treatment.

End

THANK YOU FOR YOUR ATTENTION