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Urine and saliva , Urine

المؤلف:  Sue Jickells , Adam Negrusz (Editors)

المصدر:  Clarkes Analytical Forensic Toxicology

الجزء والصفحة: 

2026-10-27

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Urine and saliva

 Urine

Urine has been used in some jurisdictions as a specimen for forensic alcohol testing. It is amenable to analysis by both the enzymatic and chromatographic methods described above. However, its major limitations are collection and interpretation. If observed, urine collection raises privacy issues; if not observed, it raises issues of chain of custody, and the potential for substitution or dilution. With respect to interpretation, urinary alcohol concentration is an indirect measurement of BAC. Urine is formed in the kidneys as an ultrafiltrate of blood. There fore, a factor must be applied to account for the higher water content. Of more importance, however, is that, since urine is formed over time, the urine alcohol concentration is an average corresponding to the blood concentration over the time during which the urine was formed and collected in the bladder. Since this can cover an appreciable amount of time (up to several hours), even a urine sample corrected for water content may not reflect the true BAC at the time of urine collection. To correct for this, for forensic purposes urine is generally collected for analysis about an hour after an initial void. The subject is directed to empty his or her bladder, after which he or she is allowed a period of time (approximately an hour) during which new urine corresponding to their current BAC is formed and collected for testing. Such complications and the associated problems of interpretation mean that urine alcohol determination is not a preferred forensic approach, although it is acceptable in many jurisdictions. Problems with interpretation are generally overcome by adopting a statutory ‘per se’ urine alcohol offence– i.e. if the measured value exceeds the set restriction, the driver is considered to be ‘impaired’ or ‘under the influence’ and an offence is deemed to have been committed.