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Sample matrices , Urine

المؤلف:  Sue Jickells , Adam Negrusz (Editors)

المصدر:  Clarkes Analytical Forensic Toxicology

الجزء والصفحة:  P271-272

2026-10-21

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Sample matrices

Urine

Urine is the preferred body fluid in all species. Its collection is noninvasive; it is generally available in sufficient quantity; and the drugs or their metabolites tend to be present in relatively high concentrations. The disadvantages are that a drug may be present as its metabolites or in a conjugated form, and the parent drug may be present only in a relatively low concentration. Furthermore, the relationship with the concentration in blood is very imprecise.

Urine is collected almost invariably by voiding naturally. Greyhounds urinate very readily after being released from their transporter; 96% of horses in Britain urinate within 1 hour of racing; humans can generally urinate at will. However, there is the problem of security. Switching of samples is clearly a possibility that must be avoided and particular care is required during the period of waiting before a sample is obtained from a dog or a horse, and because of the desire for privacy on the part of a person. It has been reported that racing cyclists have carried a rubber bladder of (negative) urine under their arm, connected by a rubber tube to the appropriate discharge point. False penises, in a variety of natural colours, are advertised on the internet for purchase. Horse handlers responsible for collecting a urine sample from their horses have been known to substitute a urine sample of their own. One laboratory even received a sample of lager purporting to be horse urine. Incidents such as these emphasise the importance of ensuring that a correct collecting procedure is observed. The WADA guidelines on urine collection (WADA 2004b) specify that urine sample collection shall be witnessed, thereby reducing the chances for supplementation or adulteration. The guidelines specify strict criteria for the entire sampling procedure to minimise the potential for tampering by the athlete or accusations of possible contamination by the sampling personnel. The odour of urine, and of the residues produced after solvent extraction, generally provide a ready distinction between the species. The presence of appreciable quantities of nicotine, cotinine, caffeine and uric acid in urine provides good evidence of a human source. Urine samples from greyhounds are caught directly in a bowl held under the animal. For horses, a container held on the end of an extending handle is generally used (e.g. a net held on a metal ring into which is inserted a polythene bag). Metal ladles are unsuitable because the noise produced by the urine that falls into them frequently inhibits the horse from urinating further.