The Stability of Urine for the Forensic Analysis of Samples in Alleged Driving-Under-the-Influence-of-Alcohol Cases – a Review and Case Report

D Thorburn Burns^a and MJ Walker^ab 

(a)  Institute for Global Food Security, The Queen’s University of Belfast, Belfast BT9 5AG, Belfast, UK
(b)  Michael Walker Consulting Ltd, BT36 5WP, Northern Ireland, UK. Correspondence should be sent to michael.walker@qub.ac.uk 

Summary

We report on the storage stability of urine as a body fluid for forensic investigation of driving under the influence of alcohol (DUI) prompted by a recent court case in which the urine sample was not properly preserved. Studies in this area are fewer than those for the stability of blood and were designed to address two separate problems:

a)   suitable preservation and/or storage conditions for forensic urine samples and whether or not alcohol production in vitro post         sampling could explain all or most of the analytical findings
     or
b)   to set clinical cut-off values for investigation and diagnosis of pathologies of carbohydrate metabolism

The accepted conclusions to the first set of questions are that any well-regulated drink-driving procedure must rely on adequate chemical preservation of the urine sample to preserve its integrity. A chilled (≤ 4⁰C) or frozen custody chain for urine samples would also suffice but must be evidentially demonstrable by suitable temperature monitoring records.

For the second question regarding the glucose content of normal urine the clinical cut-off values are conservative to ensure adequate patient care and are not suitable for forensic purposes. In view of the data found in our review it would seem prudent to assume that a random urine sample from a healthy subject could have a glucose content in the upper part of the published ranges, say 60 mg/100mL, which could, if fully converted, contribute 30 mg/100mL alcohol. Thus, for a urine sample without preservative or proven chilled (≤ 4⁰C) storage an alcohol result of up to 30 mg/100mL above a statutory urine limit could be unsafe to sustain a conviction.

The importance of the correct sampling procedure and sample temperature monitoring records should be the subject of adequate regular refresher training for any police officer authorized to take urine samples.

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