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Specimen types , Urine

المؤلف:  Sue Jickells , Adam Negrusz (Editors)

المصدر:  Clarkes Analytical Forensic Toxicology

الجزء والصفحة: 

2026-10-11

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Specimen types

Urine

Urine is a useful fluid for toxicology testing, as it comprises more than 99% water and contains relatively few endogenous substances that inter fere with chromatography or immunoassay tests. However, there are three disadvantages with urine in postmortem work. Firstly, urine is only available in about 50% of deaths as it is fairly common for the bladder to be voided during the dying process. It is therefore unwise to develop an analytical protocol for post mortem testing that relies solely on the presence of urine for the detection of drugs. Secondly, many drugs are metabolised so extensively that the parent drug is not detected in urine, or is present only at a relatively low concentration. However, if the metabolites are searched for, urine can be a useful fluid, especially for inexpensive methods such as thin layer chromatography (TLC), in which the metabolite patterns of the tricyclic antidepressants and phenothiazines can be diagnostic. The third disadvantage of urine is that urinary concentrations of most drugs are difficult, if not impossible, to interpret. The correlation between the concentration of drugs in urine and blood is extremely poor. The primary reason for this is that urine is not a circulating fluid but is a waste product collected in the bladder. The concentrations of drugs and metabolites in urine therefore depend on the time of urine formation relative to sampling and drug ingestion. Urine has the advantage of a longer detection window– i.e. drugs can often be detected in urine for a longer period than in blood.