sufficient sample is obtained, this should be divided between unpreserved and preserved (fluoride) tubes, otherwise the entire sample should be preserved unless there is a possibility of poisoning with fluoride or compounds giving rise to fluoride in vivo such as fluoroacetate. Added fluoride may also enhance decomposition of organophosphorus compounds (Moriya et al., 1999). If only heart or cavity blood is available this should be clearly stated.
Post-mortem blood (ca. 20 mL) for qualitative analysis only should be taken from the heart (preferably right atrium), inferior vena cava, or another convenient large vessel. The precise sampling site must be recorded on the sample tube. The blood should be free-flowing.
2.3.3 Urine
The presence of metabolites may sometimes assist identification of a poison if chromatographic techniques are used, but not all poisons appear in urine as either parent compound, or metabolites. A 50 mL specimen from an adult, collected in a sealed, sterile container, is sufficient for most purposes. No preservative should be added. The sample should be obtained as soon as poisoning is suspected, ideally before any drug therapy has been initiated. However, some drugs, such as the tricyclic antidepressants (amitriptyline, imipramine, etc.), cause urinary retention, and a very early specimen may contain insignificant amounts of drug. Conversely, little poison may remain in specimens taken many hours or days after exposure even though the patient may be very ill, for example as in acute paracetamol poisoning.
High concentrations of some drugs or metabolites can impart characteristic colours to urine (Table 2.7). Strong smelling poisons such as camphor, ethchlorvynol, and methylsalicylate can sometimes be recognized in urine because they are excreted in part unchanged. Acetone, an endogenous metabolite, may arise also from metabolism of 2-propanol (Section 1.2.3). Chronic therapy with sulfa-drugs such as a sulfonamide may give rise to yellow or green/brown crystals in neutral or alkaline urine. Phenytoin, primidone, and sultiame may give rise to crystals in urine following overdosage. Surgical manipulation of paralytic ileus may promote absorption of orally administered methylene blue (Morell-Garcia et al., 2016). Characteristic colourless crystals of calcium oxalate may form at neutral pH after ingestion of ethylene glycol, oxalic acid, or water-soluble oxalates (Hanouneh & Chen, 2017; Section 22.4.1.2). Urine fluorescence may be due to fluorescein added to car antifreeze (often contains ethylene glycol and/or methanol) and possibly other products to aid leak detection.
Table 2.7 Some possible causes of coloured urine
| Colour | Possible cause |
| Yellow/brown | Bilirubin, haemoglobin, myoglobin, porphyrins, urobilin Anthrone derivatives (e.g. from aloin, aloe, cascara, senna, rhubarb, etc.),a bromsulfthalein,a carotenes, chloroquine, congo red,a cresol, flavins (yellow/green fluorescence), fluorescein, mepacrine, methocarbamol (on standing), methyldopa (on standing), nitrobenzene, nitrofurantoin, pamaquine, phenolphthalein,a primaquine, quinine, santonina |
| Red/brown | Bilirubin, haemoglobin, myoglobin, porphyrins, urobilinAminophenazone, anisindione,a anthrone derivatives,a bromsulfthalein,a cinchophen, congo red,a cresol, deferoxamine,b ethoxazene, furazolidone, furazolium, levodopa (black on standing), methocarbamol, methyldopa, niridazole, nitrobenzene, nitrofurantoin, phenacetin, phenazopyridine, phenindione,a phenolphthalein,a phenothiazines, phensuximide, phenytoin, pyrogallol, rifampicin, salazosulfapyridine, santonin,a sulfamethoxazole, warfarin |
| Blue/green | Bile, biliverdin, indican (on standing)Acriflavine (green fluorescence), amitriptyline, azuresin, copper salts, ingido carmine, indometacin, methylene blue,b nitrofural, phenylsalicylate, resorcinol, toluidine blue,b triamterene (blue fluorescence), flunitrazepam (blue fluorescence) Methadone linctus adulteration |
| Blackc | Blood (on standing), homogentisic acid, indican (on standing), porphobilinCascara (on standing), levodopa (on standing), phenols including propofol, pyrogallol, resorcinol, thymol |
apH dependent
bSometimes given i.v. to treat poisoning
cSome urinary bacteria possess an enzyme able to convert a tryptophan metabolite into a substance that interacts with the plastic of urine collection bags to produce indirubin (red) and indigo (blue) giving an intense purple/black colour. Although dramatic, purple urine bag syndrome is harmless and disappears after treatment of the infection (Kumar et al., 2018)
For post-mortem work, if possible, 2 x 25 mL urine samples should be collected in sterile plastic container(s), one with preservative (2 % w/v fluoride). Ethanol may be produced (Foley, 2018), and also degraded by microbial action, unless appropriate precautions are taken. If only a small amount of urine is available, all should be preserved with fluoride (but see note on fluoride poisoning above) in a plain 5 mL plastic or glass tube. Boric acid or thiomersal [thimerosal; sodium 2-(ethylmercuriothio)benzoate] containers should NOT be used because of sample contamination with borates and mercury, respectively. Urine specimens collected post-mortem are valuable in screening for drugs or poisons, particularly illicit drugs, and are often used for quantitative ethanol or GHB analysis to corroborate the results of a blood analysis (Sections 22.4.1.1 and 22.4.11, respectively).
2.3.4 Stomach contents
Gastric lavage is rarely performed nowadays in treating acute poisoning. However, if a sample of stomach contents is obtained soon after a poisoning episode, large amounts of poison may be present while metabolites may be absent. When investigating possible poisoning, it is important to obtain the first sample of any lavage fluid because later samples may be very dilute. A representative portion (ca. 50 mL) without preservative should be taken for analysis. However, all stomach contents should be retained and the volume noted, and this information passed to the laboratory. If the blood concentration is difficult to interpret, most notably in post-mortem work, it can be helpful to measure the amount of poison present in the stomach.
Stomach contents are especially useful if poison(s) which are not easy to measure reliably in blood such as cyanide have been taken orally. However, great care is needed if cyanide salts or phosphides, for example aluminium phosphide, are thought to have been ingested, particularly on an empty stomach, because highly toxic hydrogen cyanide or phosphine gas may be released because of reaction with stomach acid. Additionally, the presence of these and other volatile materials can lead to cross-contamination of other biological specimens unless due precautions are taken.
With stomach contents (and also scene residues – Section 2.3.20), characteristic colours or smells (Table 2.8) may indicate a variety of substances. Many other compounds (for example, ethchlorvynol, methylsalicylate, paraldehyde, phenelzine) also have distinctive smells. Very low or high pH values may indicate ingestion of acids or alkali, while a green/blue colour suggests the presence of iron or copper salts.
Table 2.8 Smells associated with particular poisons.
