Urine Alcohol Concentration and Urine Alcohol Test

How is a urine alcohol test done?

A tested person empties the bladder completely and then, after 20-60 minutes, provides at least 45 milliliters (about 1.5 fl. oz) of urine ^[4]. To stimulate urination, the person may drink up to 40 oz (about 1 liter) water before the test ^[4].

How accurate is a urine alcohol test?

In legal procedures in the U.S. the urine alcohol concentration (UAC) is considered to be 1.3 times as high as blood alcohol concentration (BAC), but this is close to the truth only for a certain period of time during which the blood alcohol concentration is falling ^[1].

The actual UAC/BAC ratios may range from as low as 0.1/1 to as high as 21/1 ^[3]. For example, low UAC/BAC ratios can be observed within the first 2 hours after drinking when there may be not much alcohol in the urine yet, and high UAC/BAC ratios can be observed when most of alcohol already disappears from the blood.

Drinking water after drinking alcohol and before the test does not significantly reduce urine alcohol concentration; it only lowers urine specific gravity ^[5].

Causes of FALSE POSITIVE Results

Errors during collecting, storing or testing urine samples may cause false positive or negative results ^[6]. For example, in an improperly stored urine sample of individuals with untreated diabetes type 1 and urinary tract infection, bacteria or fungi can convert glucose to ethanol ^[7].

Causes of FALSE NEGATIVE urine alcohol test

• When the test is performed within 2 hours after stopping drinking, that is when the urine alcohol concentration (UAC) may be still lower than blood alcohol concentration (BAC), using the official UAC : BAC ratio 1.3 : 1 could result in a false negative estimation of BAC ^[8].
• When not supervised, a tested person could add water into the urine sample and thus lower its alcohol concentration. Such manipulation can be easily recognized by checking the temperature and composition of the urine sample, though.

Ethyl Glucuronide (EtG) and Ethyl Sulfate (EtS) Urine Test

Ethylglucuronide (EtG) and ethyl sulfate (EtS) are products of ethanol degradation in the body. EtG and EtS can be produced only from ethanol and not from other alcohols, such as methanol or isopropanol, or other metabolic processes in the body, so EtG urine test is specific for an ethanol consumption ^[9]. EtG and EtS may be excreted in the urine for as much as 5 days after alcohol consumption ^[10]. A commonly used level at which an EtG urine test is considered positive is 500 ng EtG/mL of urine, but different laboratories may use levels ranging from 100 to 1,000 ng/mL ^[10].

When is an EtG urine test done?

An EtG test can be done to check for alcohol consumption in workplaces, alcoholism treatment programs or in those on probation after professional or driving license suspension ^[11].

How accurate is an EtG urine test?

• After 1 drink, an EtG urine test may be positive (above 100 ng EtG/mL) for less than 24 hours (or longer), and after 2-4 drinks for less than 48 hours (or longer) ^[10,12]. In heavy drinkers, EtG urine tests were positive (above 500 ng EtG/mL) for 4o-13o hours after admission to the hospital ^[10].
• After the same amount of alcohol drunk, there may be great differences in the urine EtG levels in one individual (after repeated tests), among different individuals or among different laboratories ^[12].

FALSE POSITIVE EtG Urine Test

Causes of a false positive EtG urine test, when a cutoff level 100 ng EtG/mL urine is used ^[13]:

• Consumption of as little as 1 gram of alcohol, for example by alcohol-containing foods (communion wine, cooking wine added to sauces and marinades,  wine or fruit vinegar, soy sauces and other condiments, vanilla extract in desserts, certain candies, overripe fruits, fruit juices, kefir, Kombucha, gravy, sauerkraut, red cabbage, jam, marzipan, raisins chocolate, pizza, bread, hot dog rolls and other yeast leavened carbohydrate foods), may result in a positive EtG urine test ^[13,14,17].
• Non-alcoholic beer (containing up to 0.5 vol% alcohol) my cause a positive EtG urine test  ^[15]. In one study, ingestion of 750 milliliters non-alcoholic wine (containing EtG, EtS and up to 0.2 grams of alcohol per liter) did not cause positive EtG, but positive EtS test ^[16].
• Ethanol from drugs and supplements, such as ethanol-containing cough, analgesic, antihistamine, multivitamin and iron syrups, nasal decongestants, asthma inhalers (theophylline), liquid anti-diarrheals and diuretics, sedatives, antipsychotics or anesthetics might cause positive EtG urine tests ^[17,21].
• Occupational exposure to vapors of alcohol beverages and ethanol-containing solvents, lacquers, denatured alcohol, air fresheners, windshield wipers, insect repellents, deodorants, perfumes, cologne, shaving lotions, hair conditioners, hand sanitizers, detergents, cleansers could potentially result in a positive EtG urine test ^{[17,18,19,20]}.
• In individuals with untreated diabetes 1 and urinary tract infection, bacteria can convert sugar in their urine to EtG but not EtS ^[7].
• According to 2 studies, using alcohol-based mouthwash up to 4 times a day may result in a positive EtG test ^[18,22].
• Technical errors in storing a urine sample before testing may result in false positive EtG test ^[6,10].
• Dehydrated individuals may have increased urine EtG levels, so they could be tested positive after non-intended alcohol consumption (alcohol-containig foods or medicines), but there is a lack of experimental studies about this issue ^[23].

FALSE NEGATIVE EtG Urine Test

• Drinking large amounts of water within 1 hour before the test results in diluted urine with lower or even false negative EtG levels ^[12]. In laboratories, an abnormal dilution of urine can be detected and the results recalculated to average urine dilution.^[10].
• Urinary tract infection (UTI) in combination with improper storing of an urine sample may cause a false negative EtG (but not EtS) test due to bacterial degradation of EtG ^[7,21,24].
• Kidney disease may decrease urine EtG levels ^[21].

How long can be alcohol detected in the urine?

Alcohol in urine can be usually detected by up to 48 hours after a last drink, or, in chronic alcoholics by up to 130 hours.