Colin MacKenzie M.D.
November 8, 2020


Excessive alcohol use can lead to many social and health problems, including the leading cause of death and disability in motor vehicle accidents. In this blog, we shall discuss the tests that are available to screen someone for alcohol use.


The CAGE and MAST are two kinds of questionnaires used to screen people for possible alcohol abuse. The simpler of the two, the CAGE, is a set of four questions with “yes” or “no” answers.[i]

The questions of the CAGE test are:[ii]

  1. Have you thought that you need to Cut down on your drinking?
  2. Have you Annoyed others with your drinking behavior?
  3. Have you felt Guilty about your drinking?
  4. Have you needed an Eye-opener to treat a hangover?

A “yes” answer to any one of these questions is an alert to possible alcohol abuse.

The MAST,[iii] or Michigan Alcohol Screening Test, is a set of 25 questions about past alcohol use. They are more detailed than the CAGE questions. Twenty-five questions may be challenging to administer, so shorter versions like the brief-MAST of 10 items and the short-Mast of 13 questions are also available.  The MAST measures alcohol use problems over one’s lifetime.  Another short survey using 10 items is called the AUDIT (Alcohol Use Disorders Identification Test)[iv] which is approved by the World Health Organization (WHO).  Each question is scored from 0 to 4 with a total score of 8 indicating harmful alcohol use and a score of 15 or more likely indicating dependence at some point over the last 12 months.   


When questionnaires such as the CAGE or MAST suggest alcohol abuse, various lab tests are available to check alcohol levels in breath, saliva, hair, blood, urine, and nails.

When alcohol is drunk, it leaves the stomach and intestines within 30 to 90 minutes and enters the bloodstream. It is then metabolized via three different enzymatic pathways (or chemical reactions) in the liver and a very small percentage is excreted unchanged in the breathe, urine, and sweat.  When these three chemical pathways in the liver metabolize alcohol, a number of different enzymatic reactions are utilized which produce chemical by-products (or chemicals that are made along the way toward, and including, the end products).   These chemical by-products, as well as the excreted alcohol, are the chemicals detected by the many tests used to identify alcohol consumption.  Enzymes that turn acetic acid into CO2 and water perform the primary chemical pathway that metabolizes over 99% of alcohol consumed. However, alternative enzymes that produce chemicals called ethyl glucuronide and ethyl sulfate metabolize a very small amount of alcohol. Either alcohol itself or these secondary chemicals form the basis for most of the alcohol tests.[vi]

Alternatively, alcohol can also cause increases in certain enzymes that can serve as the basis for alcohol tests.


A variety of instrument and lab tests can detect the timing and duration of alcohol use.  Some detect recent use, others short- term use, and some others long- term (or chronic) use of alcohol[vii].

Probably most people have heard of the breathalyzer test.[viii] Though the term “breathalyzer” used to refer to only one type of technology used, it is now often used generically to imply any of three different types of technology used to detect alcohol in exhaled air.  These tests are often used by law enforcement to screen drivers for recent alcohol use according to the criteria set by different states for unsafe levels. The breathalyzer tests that measure alcohol levels in the breath is easy to use and gives immediate results. As mentioned previously, a very small portion of alcohol consumed moves from the gastrointestinal tract to the lungs without being metabolized (or broken down into other chemicals).  Alcohol is a volatile substance, meaning that it evaporates from solution, in this case, the blood.  Once alcohol is in the small blood vessels (capillaries) of the lungs’ alveolar sacs, it will evaporate from the blood, move across the cellular membranes of the capillaries and alveoli, and enter the air inside your lungs, where it is exhaled. The concentration of the alcohol in the exhaled air roughly correlates with the amount of alcohol in the blood by a ratio of 2,100:1, meaning the amount of measured alcohol in 2,100 milliliters of air is the amount in 1 milliliter of blood.[ix]  Thus, using this ratio, it is possible to measure the concentration of alcohol in blood based on the concentration of alcohol in exhaled air. The devices then calculate a blood alcohol content of “BAC”.  Most states use a BAC of 0.08% as the legal limit of intoxication. A BAC of 0.08% is equivalent to 0.08 grams of alcohol in 100 milliliters of blood.[x]  These measurements are often challenged in court, and in many states, blood tests must back them up.  As mentioned previously, there are three different types of technologies that are used in the most common “breath tests” for alcohol.  One uses photocell technology, another uses infrared technology, and the other uses modern day fuel cell technology.

There exist many different body tissue tests for alcohol ranging from blood to urine to hair as substrates.  Besides testing directly for alcohol, many tests measure direct and indirect biomarkers for alcohol.  Direct biomarkers are those that detect the by-products of alcohol metabolism while indirect biomarkers are those molecules or cells that undergo changes as a result of alcohol consumption.[xi] 


Blood tests that measure alcohol directly use the Mass Spectroscopy/Gas Chromatography (MS/GC) method and are specific for both alcohol itself and its metabolic byproducts.[xii]  The results are far more reliable and accurate than a breathalyzer test.  However, one shortcoming is that the test can only detect alcohol during acute intoxication while the alcohol is still in the blood stream. Alcohol is broken down rapidly in the body, so blood tests are most useful for alcohol use that has occurred within the last eight hours. The MS/GC method must be done in specialized labs and takes a minimum of 24-48 hours to get results.  Saliva tests are popular for workplace testing because they are portable, easy to use, and give results in minutes.  Detecting alcohol with saliva is possible because it is secreted by the salivary glands. The tests can detect alcohol immediately upon ingestion and for up to about eight hours after use.


Perhaps the most popular test is the ethyl glucuronide (EtG) test done on a urine specimen.[xiii] EtG, as mentioned above, is produced in very small quantities by enzymes found in the liver and is then excreted unchanged in the urine.  EtG appears in blood within 45 minutes of alcohol consumption and after 60 minutes in the urine.  It can remain detectable in the urine up to 40 to 130 hours after heavy alcohol consumption.  EtG is a very stable molecule and can remain detectable at consistent concentrations for over five weeks in a urine sample.  One study found that age, gender, renal disease, cannabis use, and amount of alcohol used over the prior month had an influence on EtG concentrations. Race, smoking, body mass index, liver disease, and total body water had no impact.  However, false positives and false negatives can result from bacterial contamination of the sample.  Thus, any positive test should be confirmed by the detection of Ethyl Sulphate (EtS), the other trace molecule produced in the liver, which is not susceptible to bacterial contamination, by the Mass Spectroscopy/Gas Chromatography (MS/GC) method.  False positives can also occur with this test if the person has used hand sanitizers with propyl alcohol or mouthwashes that contain alcohol.  EtG is also detectable in hair and nails for up to 3-6 months. 

One way to detect long-term alcohol use is with the Fatty Acid Ethyl Esters (FAEE) test done on a hair sample. During use, alcohol reacts with fatty acids producing a group of abnormal fatty acids called Fatty Acid Ethyl Esters.  This test can detect the ongoing use of alcohol for ten months to two years. FAEE levels can go up for as long as 6-9 months after abstinence before they begin to go down again.  However, false positives can result from cosmetic hair products containing alcohol. 

An increasingly popular test is the PEth or Phosphatidylethanol test.[xiv]  PEth is a type of phospholipid molecule made when alcohol reacts with a certain cell membrane phospholipid called phosphotidylcholine, which is found in red blood cells.  It is over 99% specific meaning it is only produced when alcohol is consumed.  The level of PEth is also not affected by age, medications, liver or renal diseases, or body weight.  Though the test can reliably detect low amounts of alcohol consumption, 47 grams for men and 32 grams for women, laboratories to confirm consumption typically use an arbitrary cut-off value of 20 ng/ml, which usually correlates to larger quantities of use. PEth is produced immediately after consumption and usually peaks within 8 hours with a half-life of about 5 hours.  False positives are also not produced by the use of mouthwashes, hand sanitizers, or cosmetics. 


Indirect biomarkers are the result of some change or damage to cells and tissues.  Thus, alcohol consumption generally has to be of significant duration and amount to create measurable quantities of these markers.  In addition, other factors, such as medications, infections, and illnesses can cause similar alterations of these biomarkers rendering them less sensitive and specific for alcohol consumption.  In addition, even when caused by excess alcohol consumption, making accurate correlations between abnormal measures of these biomarkers and amounts or duration of alcohol use is not possible. Regardless, these biomarkers have been in use for decades and include the liver enzymes aspartate aminotransferase (AST), alanine aminotransferase (AST), and gama-glutamyl transferase (GGT).  The red blood cell parameter called mean corpuscular volume (MCV) can also be analyzed as well as an iron transport protein called carbohydrate deficient transferrin (CDT%).[xv] 

Carbohydrate deficient transferrin (CDT%) is a protein responsible for transporting iron from the blood into the bone marrow, liver, and spleen.  It usually contains four carbohydrate chains on the base molecule, but with alcohol consumption of at least 5 drinks per day for two or more weeks, an abnormal percentage of CDT with less than four carbohydrate chains is produced (thus the name carbohydrate deficient transferrin). 

Mean corpuscular volume (MCV) is a measure of the volume (size) of red blood cells.  When alcohol use is excessive for at least eight weeks, the volume of red blood cells increases.  However, other diseases can cause red cell volume to increase as well making this test less sensitive, but it has higher specificity than many other indirect biomarkers. 

Gama-glutamyl transferase (GGT) is one of the most commonly used indirect biomarkers.  It is a glycoenzyme used by endothelial cells of various organs, especially the liver, for glutathione metabolism and peptide transport.  Blood levels rise due to damaged and dead cells after several weeks of consistent alcohol consumption.  It has lower sensitivity with a high false negative rate as only approximately 22% to 35% of heavy drinkers demonstrate elevated levels. It takes about two to six weeks of abstinence to return to normal levels. 

The liver enzymes AST and ALT are found in liver cell cytoplasm and are released when liver cell membranes become permeable from alterations due to alcohol.  Though ALT is less sensitive than AST, ALT is found exclusively in the liver.  Neither enzyme is particularly sensitive for excessive alcohol use, however some studies cite a ratio of AST/ALT of >2 to be indicative of heavy use as opposed to other causes of liver damage.  


Questionnaire tests can screen people for possible alcohol use, and a variety of lab tests can provide varying measures of just how much alcohol a person has been drinking either in the short-term or the long-term.


[i] Gül S, Akvardar Y, Ta? G, Tuncel P. Alkol Kullanim Bozukluklarinda Tarama Testleri ve Laboratuvar Belirteçlerinin Tanisal Etkinli?i [The diagnostic validity of screening tests and laboratory markers in alcohol use disorders]. Turk Psikiyatri Derg. 2005 Spring;16(1):3-12. Turkish. PMID: 15793693.

[ii] Ewing JA. Detecting alcoholism. The CAGE questionnaire. JAMA. 1984 Oct 12;252(14):1905-7. doi: 10.1001/jama.252.14.1905. PMID: 6471323.

[iii]Fonte A, Mota-Cardoso R. MAST e AUDIT. Avaliação de características psicométricas em doentes com dependência de álcool [MAST and AUDIT. Evaluation of psychometric characteristics in patients with alcohol dependence]. Acta Med Port. 2013 Jul-Aug;26(4):335-40. Portuguese. Epub 2013 Aug 30. PMID: 24016641.

[iv] Saunders JB, Aasland OG, Babor TF, de la Fuente JR, Grant M. Development of the Alcohol Use Disorders Identification Test (AUDIT): WHO Collaborative Project on Early Detection of Persons with Harmful Alcohol Consumption--II. Addiction. 1993 Jun;88(6):791-804. doi: 10.1111/j.1360-0443.1993.tb02093.x. PMID: 8329970.

[v] Cederbaum AI. Alcohol metabolism. Clin Liver Dis. 2012;16(4):667-685. doi:10.1016/j.cld.2012.08.002

[vi] https://pubs.niaaa.nih.gov/publications/aa72/AA72.pdf




[x] https://en.wikipedia.org/wiki/Blood_alcohol_content

[xi] Andresen-Streichert H, Müller A, Glahn A, Skopp G, Sterneck M. Alcohol Biomarkers in Clinical and Forensic Contexts. Dtsch Arztebl Int. 2018;115(18):309-315. doi:10.3238/arztebl.2018.0309

[xii]Sharma P, Bharat V, Murthy P. Quantitation of ethyl glucuronide in serum & urine by gas chromatography - mass spectrometry. Indian J Med Res. 2015;141(1):75-80. doi:10.4103/0971-5916.154507

[xiii]McDonell MG, Skalisky J, Leickly E, et al. Using ethyl glucuronide in urine to detect light and heavy drinking in alcohol dependent outpatients. Drug Alcohol Depend. 2015;157:184-187. doi:10.1016/j.drugalcdep.2015.10.004


[xv] Gough G, Heathers L, Puckett D, et al. The Utility of Commonly Used Laboratory Tests to Screen for Excessive Alcohol Use in Clinical Practice. Alcohol Clin Exp Res. 2015;39(8):1493-1500. doi:10.1111/acer.12780

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