Alcohol testing is used to determine whether a person has been drinking alcohol recently. Several approaches are used to determine alcohol usage. These include directly measuring the amount of ethanol present in a person’s blood, determining the amount of alcohol in exhaled air (the so-called breathalyser test), or measuring markers of alcohol consumption in the blood, hair, nails, urine, or sweat.
This article provides an overview of the most widely used methods for alcohol testing as well as factors that should be considered before any alcohol test is implemented.
Blood alcohol content testing
Specifically, a blood alcohol concentration or blood alcohol content test (BAC test) determines the concentration of ethanol in venous blood, yielding a result expressed as grams (of ethanol) per 100 mL of blood.
Some vendors offer BAC testing using breath, saliva, or urine samples, but BAC testing based on venous blood is widely viewed as the most accurate and reliable approach. Because the water present in blood can evaporate, blood samples taken for BAC testing must be stored in capped tubes for accurate results based on volume, and BAC cannot be analysed from dried samples.
The principle behind BAC testing is this: when people drink alcoholic drinks, the ethanol in those drinks is quickly absorbed into the bloodstream and broken down by the liver. If a person drinks faster than the liver can break down the ethanol, the blood ethanol concentration will rise. BAC tests can typically detect alcohol in the blood for up to 12 hours after the last drink was taken.
Testing for chronic alcohol consumption
In addition to the BAC tests that directly measure ethanol, other blood tests can measure substances that accumulate in the blood because of chronic alcohol use.
The PEth test measures the levels of phosphatidylethanol or PEth in the blood and can be applied to venous blood or microsamples of capillary blood. PEth is a phospholipid that exists naturally in red blood cells, and its formation in the blood is catalysed by the enzyme phospholipase D in the presence of ethanol. PEth accumulates with frequent alcohol consumption and has a half-life in the blood of approximately 4 days, making it a useful biomarker for chronic alcohol consumption, with a window of detection of around 2-4 weeks.
Other blood-borne markers for long-term alcohol consumption include carbohydrate-deficient transferrin (CDT), gamma-glutamyl transferase (GGT), ethyl glucuronide (EtG) and ethyl sulfate (EtS).
CDT is one of several transferrin proteins produced by the liver, and it is usually used to identify cases of early chronic alcohol usage, to identify alcohol addiction, and in the follow-up of individuals in addiction rehabilitation programmes. CDT bloodstream levels are elevated during chronic alcohol consumption, return to normal within a couple of weeks of abstinence, and rise again within days of a relapse. CDT can be detected in small volumes of capillary blood collected via fingerprick sampling.
Although both are widely used, CDT is considered to be a more specific marker of chronic alcohol consumption than GGT, a liver enzyme that aids in digestion. Elevated GGT levels are seen in about half of all chronic heavy drinkers, but elevated GGT in the blood can also be an early indicator of liver disease in the absence of chronic alcohol consumption. However, while GGT is not a specific or sensitive marker for the reasons mentioned above, it is often used in a liver function panel that includes other liver enzymes such as aspartate transaminase (AST) and alanine transaminase (ALT), which can collectively help to determine whether an individual might have liver disease, a bone disorder, or consumes excess alcohol.
EtG and EtS are direct metabolites that arise through the breakdown of ethanol. These are formed upon consuming even small amounts of alcohol and are easily detected in the urine for up to 70-80 hours in the case of heavy drinking. EtG can also be detected in the blood, hair or on the breath, but it is most widely applied to urine samples. Despite its sensitivity, EtG is most useful as a qualitative rather than quantitative test for alcohol consumption, because many factors affect EtG levels upon drinking which makes it difficult to directly correlate high EtG levels with high alcohol consumption.
When and where is alcohol testing used?
Since direct blood alcohol testing can determine whether someone has been drinking in recent hours, it is often used in criminal investigations, e.g., suspected drink-driving and road traffic accidents, to identify underage drinking, and to monitor individuals as part of parole agreements.
BAC tests are also used in hospitals to check for alcohol poisoning, which can be life-threatening if untreated, as well as in workplaces that require driving or other operation of heavy machinery to ensure staff safety.
Tests to identify long-term alcohol consumption are useful in diverse settings, including occupational health, family (custody) law and forensic medicine. Other uses include monitoring of patient eligibility for organ transplantation, e.g., to ensure that a prospective liver transplant recipient is not drinking alcohol, and to monitor individuals as part of addiction recovery programmes.
Important considerations for implementing alcohol testing
So far, we’ve provided an overview of the current approaches and scenarios that warrant alcohol testing. Let’s now look at some key factors must be considered before implementing any alcohol test in a given setting.
Choosing the right marker and test
First and foremost, the choice of marker and testing strategy should be matched with the testing goal and the timeframe. For instance, is the person currently under the influence of alcohol or are they likely to have been drinking at an event that happened the day before? Or does an individual have an abusive or harmful drinking pattern, but is not under the influence of alcohol at the time of sampling?
While exceptions may exist, the table below provides a simple overview of when to use which marker and sample type.
Testing goal and timeframe | Under the influence now | Recent drinking | Risky, harmful drinking | Chronic abuse, risk of organ damage |
Marker | ethanol | EtG, EtS | CDT, PEth | GGT, AST, ALT |
Sample type | breath, blood, urine, saliva, sweat | urine, blood, hair | blood | blood |