When alcohol is ingested, it is absorbed directly from the proximal small intestine and distributed throughout the entire fluid space of the body. After equilibrium is reached, alcohol will be found in all tissues of the body in proportion to their water content. Urine is the most practical specimen for alcohol testing in the workplace, when the purpose of testing is to demonstrate that alcohol consumption has occurred. Peak urine alcohol levels are reached 45 to 60 minutes after alcohol ingestion. At this time, urine alcohol levels are typically about 1.3 times greater than the corresponding blood alcohol concentration. This ratio is only valid during the elimination phase, which occurs after the blood alcohol level has peaked and is decreasing. Alcohol may be detected in the urine for 1 to 2 hours longer than it is detected in blood.
The presence of alcohol in the urine indicates recent prior use, but may not correlate with the degree of intoxication observed at the time the specimen is provided. Increments of urine continuously pool in the bladder, and each contains a different amount of ethanol. The ethanol level from such a sample relates only to the average blood alcohol concentration during the time needed for the voided urine sample to accumulate in the bladder and not to the blood alcohol concentration at the time of collection. False negative results may be caused by the volatility of alcohol. Urine alcohol concentrations may decrease 10 to 25% during each hour that a urine sample remains uncapped prior to testing.
Diabetic patients who are spilling glucose into their urine and have a urinary tract infection with a fermenting organism, like Candida albicans, may have a positive test even though they did not consume alcohol.
Estimation of blood alcohol concentration from urine alcohol measurements is more reliable if two urine samples are collected about 30 minutes apart. The first urine is usually discarded and the second one is used to estimate blood alcohol concentration. The limitation of a single first-void urine sample is that one does not know over what time period the urine has collected in the bladder. However, subjects who have been drinking usually do not retain urine in their bladders for an extended time period because of the diuretic effect of alcohol.
At least 35 states authorize urine alcohol measurements for driving related offenses. Some regulatory and legal agencies use a 1.5:1 urine to blood ratio, instead of 1.3:1, to be conservative and give the benefit of any doubt to the subject.
Reference value is not detected.
Specimen requirement is a freshly voided random urine sample of 25 mL. A Drug Screen Kit should be used for chain of custody testing.
