While some drugs can show up in a person’s urine for days or weeks, alcohol has a much shorter detection window. A urine screening can typically detect ethanol — the type of alcohol found in alcoholic beverages — for up to 12 hours.
There are other types of urine tests that can identify traces of alcohol byproducts for up to 72 hours after a person’s last drink, but those tests have significant limitations.
Alcohol Detection Windows
The vast majority — somewhere between 90 and 95 percent — of alcohol a person consumes is broken down by the liver. A tiny amount is expelled through a person’s breath and sweat. The remaining 1 to 2 percent is excreted in urine.
Alcohol will usually show up in a person’s urine within an hour of drinking, and it usually remains detectable for up to 12 hours. The actual timeframe may vary, depending on a number of factors, including weight, health, gender and the amount of alcohol consumed.
Urine alcohol content is sometimes used to estimate a person’s blood alcohol content. The amount of alcohol in a person’s urine is approximately 1.33 times greater than the amount of alcohol in their bloodstream. For accuracy, at least two urine samples are usually collected 30 minutes to an hour apart.
Byproducts Remain in Urine Longer
While alcohol itself has a relatively short detection window of only a few hours, certain alcohol byproducts remain in the body longer.
One of these byproducts, ethyl glucuronide (EtG), can be detected in urine for up to three days after a person’s last drink. Some labs also test urine for ethyl sulfate (EtS), another metabolite that signals recent alcohol intake.
EtG and EtS tests are sometimes used by courts to see if people on probation are complying with requirements that they remain abstinent from alcohol. Some rehab programs also use the tests to monitor people in treatment and identify a potential relapse.
Disadvantages of EtG/EtS Urine Testing
While EtG and EtS urine tests provide a much longer detection window for alcohol use, they have several drawbacks.
The testing is not as widely available as a standard urine screening for ethanol, and it costs more. EtG/EtS testing also can’t tell you how much alcohol a person consumed. And it’s unable to differentiate between ethanol from alcoholic beverages and exposure to alcohol from other products.
Individuals who’ve used over-the-counter flu and cold medications and mouthwashes that contain alcohol may end up testing positive for EtG or EtS. Even topical use of other products that contain alcohol — such as body sprays, insecticides and hand sanitizer — can result in a positive EtG/EtS test.
Dangers of False Positives
In 2011, researchers at the University of Florida examined 11 study subjects who were completely abstinent from alcohol to see whether or not the frequent use of hand sanitizer would affect urine levels of EtG and EtS.
For three consecutive days, the research subjects applied hand sanitizer to their hands every five minutes — roughly the same amount a nurse would use during a typical workday. Nearly all of the subjects tested positive for EtG, according to the study’s findings, which were published in the Journal of Analytical Toxicology.
In a press release, lead researcher Dr. Gary Reisfield, an assistant professor of psychiatry at the University fo Florida, said the findings underscore a key problem with EtG testing. “We really cannot tolerate false positives. Falsely accusing someone of alcohol abuse can have potentially devastating effects personally and occupationally.”