Principle
There is a predictable relationship between blood alcohol concentration and urine alcohol concentration. Because of this, urine analysis is an accurate and reliable means of assessing alcohol intoxication. It has a well established basis within forensic science and law enforcement.
Because of the predictability of the blood/urine relationship, there is statutory control of urine alcohol concentration.
The UK legal limit for driving is 80 mg% in blood - this is equivalent to a urine alcohol concentration of 107 micrograms%.
The results from urine testing can be used evidentially or for screening purposes.
Analysis
Urine analysis for alcohol takes place in the laboratory, where accurate chromatographic analysis produces definitive quantitative and qualitative identification.