Important Considerations for Implementing Alcohol Testing

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

The most commonly used markers and their window of detection.


An accurate test result is paramount when determining alcohol consumption, since the wrong result can have disastrous outcomes, e.g., a false-positive result could mean someone losing visitation rights to their children, or being convicted of a drink-driving offence they didn’t commit. Similarly, a false-negative result could allow someone to continue drinking to excess and putting their own and other’s lives at risk.

Beyond the legal and social implications of inaccuracy, when alcohol testing is included in the medical workup for an individual who may have liver disease, an inaccurate result could lead to a treatable disease going unnoticed.


We believe that alcohol testing should be flexible with regards to testing location. Breathalysers are currently used in some workplaces to check for alcohol consumption, but their accuracy has been hotly debated, and studies have shown that BAC estimates based on breathalyser testing (BrAC estimates) are consistently lower than actual venous BAC by up to 15% (1,2).

For workplaces and individuals that require regular testing, the need for a trained phlebotomist to take venous blood samples can be costly and logistically challenging, especially if testing is required in remote areas.

In such scenarios, the possibility for fingerprick microsampling with a volumetric blood collection device such as Capitainer®B would be very advantageous, particularly because the resulting dried blood sample could be sent by regular postage to a suitable testing laboratory for biomarkers where dried blood is feasible. Similarly, the Capitainer®B Vanadate microsampling device offers a flexible dried blood spot (DBS) sampling solution for easy and accurate PEth testing.


In current practice, individuals suspected of drink-driving are initially asked to take a breathalyser test at the roadside. However, as mentioned above, breathalyser tests are not always accurate. Several factors can lead to false- negatives or positives, including the weather. For instance, cold weather can result in condensation on the breath, which may be mistakenly interpreted as alcohol by a breathalyser device.

Therefore, in practice, a positive breathalyser result is typically followed up with a venous blood alcohol test performed by a medical professional. This usually requires that a doctor is called out to the police station, which is inconvenient and may result in the suspect being held for a period of time. Another risk associated with current practice is that some/all the alcohol may be metabolised and no longer present in the blood by the time the doctor reaches the station to take a venous blood sample.

The possibility to take a blood sample at the roadside would be cost-saving for police departments, and much more convenient for all parties, especially those individuals unfortunate enough to achieve a false-positive breathalyser test.

Patient comfort

Depending on the reason for testing, a person might need to be tested regularly, e.g., when on parole or in a workplace that demands regular monitoring for alcohol use.

Regular venous blood testing can be uncomfortable and inconvenient, which can result in people not wanting to be tested at all. In such cases, a microsampling device could be a more comfortable and easy solution.


  1. Jones AW, Andersson L. Comparison of ethanol concentrations in venous blood and end-expired breath during a controlled drinking study. Forensic Sci Int. 2003 Mar 12;132(1):18-25. doi: 10.1016/s0379-0738(02)00417-6.
  2. Kriikku P, Wilhelm L, Jenckel S, Rintatalo J, Hurme J, Kramer J, Jones AW, Ojanperä I. Comparison of breath-alcohol screening test results with venous blood alcohol concentration in suspected drunken drivers. Forensic Sci Int. 2014 Jun; 239:57-61. doi: 10.1016/j.forsciint.2014.03.019.

MedlinePlus.  Blood Alcohol Level ( Accessed 4th October 2023.


outstanding technical support


we offer a full product guarantee


we offer free delivery to UK universities and non profit organisations