Scientific methods of analysis for
poisons have only recently been developed. Until the 19th century, doctors and
scientists harboured faulty notions about the effect of poisons on the human
body. It was believed that if a dead body was black, blue, or spotted in
places, or “smelled bad”, the cause of death was a poison. Other fallacious
ideas were that the heart of a poisoned person could not be destroyed by fire,
and that the body of a person dying from arsenic poisoning would not decay. The
first person to suggest a method for detecting poisons in tissues was the Dutch
physician Hermann Boerhoave who theorised that various poisons in hot vaporous
condition yielded typical odours. He placed substances suspected of containing
poisons on hot coals and tested their smells.
Owing to the widespread use of
arsenic as a homicidal poison in the middle ages, it is small wonder that the
first mile-stones in the chemical isolation and identification of a poison in
body tissues and fluids centred around arsenic. In 1775, Karl Wilhelm Scheele,
the famous Swedish chemist, discovered that white arsenic (arsenic trioxide)
was converted to arsenious acid by chlorine water, and the addition of metallic
zinc reduced the arsenious acid to arsine gas. Gently heating the ensuing gas
led to deposition of metallic arsenic on the surface of a cold vessel. In 1821,
Sevillas utilised the decomposition of arsine for the detection of small
quantities of arsenic in stomach contents and urine in poisoning cases. In
1836, James M Marsh, a London chemist developed the first reliable method to
determine an absorbed poison (arsenic) in body tissues and fluids such as
liver, kidney and blood.
We have come a long way since then
to the present era of sophisticated analytical techniques which can detect even
micrograms of virtually any poison in almost any kind of biological specimen.
Today, an analytical (toxicology) labora-tory has become a vital adjunct to the
proper management of poisoned patients. However it is to be noted that the
cornerstone of the management of such patients—intensive supportivetherapy—is mostly independent of the kind of
poison impli-cated, and hence routine employment of expensive analytical
techniques should be avoided. The attending physician must be judicious in
calling for necessary investigations, and exercise discretion in the choice of
tests to be done.
potential indications for seeking the assistance of a toxicology laboratory are
as follows :
assess the outcome of a case of poisoning.
toxicokinetics and mechanisms of toxicity.
court, or law enforcement officer.
treatment measures and their efficacy.
the nature of poison.
assess the seriousness of a given case.
confirmation of toxic exposure.
the 7 indications mentioned can be remembered by the mnemonic
Mahoney and associates have
categorised treatment ofa poisoning case into 4 groups with respect to
· Toxicity correlates very well with
serum levels, and specific drug therapy can be instituted, e.g. digoxin,
ethylene glycol, lithium, methanol, paracetamol, salicylates, theophylline.
· Toxicity correlates closely with
serum level, but only non-specific care is required, e.g. barbiturates,
· Toxicologic testing only serves to
confirm fairly clear-cut clinical parameters suggestive of poisoning, e.g.
cyanide, narcotics, organophosphates, tricyclics.
· Toxicity correlates poorly with
serum level, and only non-specific care is required, e.g. amphetamines,
benzodiaz-epines, cocaine, hallucinogens, neuroleptics.
In fact, most poisoned patients can
be treated successfully without any contribution from the laboratory other than
routine clinical biochemistry and haematology. This is particularly true for
those cases where there is no doubt about the poison involved and when the
results of a quantitative analysis would not significantly affect therapy. In
those cases where an analytical toxicological investigation is deemed
beneficial, an orderly progression is desirable in the performance of necessary
tests and their interpretation (Table