The presence of ethanol in the urine indicates ingestion of alcohol within the past 8 hours. Detection of ethanol in the urine of a patient in an alcohol treatment program suggests failure to abstain from drinking and may indicate relapse.
The urine ethanol concentration represents an average of the blood alcohol concentration during the time period during which the urine accumulates in the bladder. In order to optimize the interpretation of a urine ethanol level, it is recommended that:
(1) the bladder be emptied (a sample of this may be used to screen for drugs of abuse)
(2) the specimen for urine ethanol testing is collected 20-30 minutes later.
ratio of ethanol in urine to that of blood during the post-absorptive phase =
= 1.3 to 1
concentration of ethanol in the blood in g/dL during the post-absorptive phase =
= (concentration of ethanol in the urine in g/dL) / 1.3
Limitations:
• The ratio is only valid during the post-absorptive, elimination phase.
• The method may be insensitive for a person with a very low blood alcohol level.
• The ratio of 1.3:1 for urine-to-blood ethanol is variable.
• The collection of the second urine specimen requires some cooperation by the person.
• This may be unreliable in post-mortem specimens and should not be used on these specimens.
• False positive urine ethanol levels can occur in a patient with both glucosuria (diabetics) and a urinary tract infection due to an organism that can ferment alcohol (Candida albicans, others). It is important that the specimen be properly stored and tested promptly.
