Fundamentals of Analytical Toxicology. Robin Whelpton

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.^a

Smell	Possible cause
Almonds	Cyanide
Cloves	Oil of cloves
Fruity	Alcohols (including ethanol), esters
Garlic	Arsenic, phosphine
Mothballs	Camphor or naphthalene
Nail-polish remover	Acetone, butanone
Pears	Chloral
Petrol	Petroleum distillates (may be vehicle in pesticide formulation)
Phenolic (carbolic soap)	Disinfectants, cresols, phenols
Shoe polish	Nitrobenzene
Stale tobacco	Nicotine
Sweet	Chloroform and other halogenated hydrocarbons

^a CARE – specimens containing cyanides may give off hydrogen cyanide gas, especially if acidified – stomach contents are often acidic. Genetic variation means that not everyone can detect hydrogen cyanide