Introduction

Alcohol testing is widely used for family court proceedings, solicitor instructions, safeguarding assessments, workplace investigations and private testing to provide objective laboratory evidence of alcohol consumption. However, there is no single alcohol test that can answer every question about a person's drinking behaviour.

Different laboratory tests measure different alcohol biomarkers, each providing information over different detection windows and reflecting different aspects of alcohol consumption. Hair alcohol testing measures the biomarkers Ethyl Glucuronide (EtG) and Ethyl Palmitate (EtPa) to help assess longer-term alcohol consumption, while blood alcohol testing may include Phosphatidylethanol (PEth), Carbohydrate Deficient Transferrin (CDT) and Liver Function Tests (LFTs) to provide information about more recent alcohol use or the physiological effects of excessive drinking.

Understanding how these alcohol biomarkers differ helps ensure the most appropriate analysis is selected for each individual case. In many legal and clinical situations, laboratories recommend combining multiple alcohol biomarkers to provide a more complete assessment of alcohol consumption than any individual test can achieve alone.

This guide explains how hair and blood alcohol testing work, what each biomarker measures, and why different alcohol tests are often used together to provide the most appropriate interpretation of alcohol consumption.

How hair alcohol testing works

Hair alcohol testing is one of the most effective ways of assessing longer-term alcohol consumption. Unlike breath or blood alcohol tests, which only indicate recent alcohol use, hair analysis measures biological alcohol biomarkers that become incorporated into the hair over time, providing an overview of alcohol consumption over a period of several months.

The laboratory analyses two internationally recognised alcohol biomarkers: Ethyl Glucuronide (EtG) and Ethyl Palmitate (EtPa).

EtPa is deposited onto the hair primarily through the scalp's sebaceous (oil) glands after alcohol has been consumed. In contrast, EtG is formed exclusively by the liver as the body metabolises alcohol before entering the bloodstream and becoming incorporated into the growing hair, primarily through sweat. The greater the concentration of these biomarkers within the hair sample, the greater the evidence of sustained alcohol consumption.

Because EtG is produced directly by the body's metabolism of alcohol, most accredited laboratories place greater emphasis on the EtG result when interpreting alcohol consumption. Measuring both EtG and EtPa together, however, provides a more complete assessment and helps support the overall interpretation of the laboratory findings.

Hair cosmetics and chemical treatments should also be considered when interpreting results. Bleaching and certain chemical treatments may reduce the concentration of EtG within the hair, which is why laboratories often recommend analysing both EtG and EtPa if hair has been chemically treated. Conversely, the regular use of alcohol-containing hair products may increase EtPa concentrations, making it important for laboratories to consider both biomarkers alongside the individual's circumstances.

The Society of Hair Testing (SoHT) recommends that alcohol hair testing is interpreted as an overview of alcohol consumption over a three- or six-month period, rather than by analysing individual segments of hair. Because alcohol biomarkers are incorporated into the hair through natural biological processes, segmenting hair for alcohol testing may lead to misleading findings and an overestimation of alcohol consumption.

For this reason, laboratories will often recommend combining hair alcohol testing with PEth blood testing when a more comprehensive assessment is required. Hair testing provides evidence of longer-term alcohol consumption, while PEth blood testing provides valuable information about more recent drinking behaviour, making the combination widely regarded as the gold standard for alcohol biomarker testing.

Hair growth rates

Hair samples can be collected from the scalp or, where necessary, from other areas of the body. However, head hair is always preferred because its growth rate is more consistent and better understood. Pubic and underarm hair are not suitable for alcohol testing due to differences in their biological growth cycles.

As a general guide:

• Head hair: approximately 1 cm represents one month's growth.
• Body hair: approximately 1 cm represents one month of growth, plus an additional delay of around 90 days before the hair emerges from the skin.

Unlike scalp hair, body hair should not be segmented or cut down for alcohol testing, meaning the entire sample is analysed.

Hair growth is not identical for every individual. Each hair follicle progresses through a natural growth cycle consisting of growing, transitional and resting phases. The telogen (resting) phase means that some hairs remain dormant before being shed, so alcohol consumed shortly before the period being assessed may still appear within the hair depending on an individual's hair growth pattern.

For this reason, hair alcohol testing should always be interpreted as an estimate of alcohol consumption over time rather than an exact calendar of drinking behaviour. Experienced laboratory scientists consider hair growth rates, the individual's circumstances and the analytical results together when providing an interpretation.

Blood alcohol testing - CDT, LFT & FBC

Blood alcohol testing provides valuable information about recent alcohol consumption and the physiological effects that excessive drinking can have on the body. Unlike hair alcohol testing, which assesses longer-term alcohol consumption over several months, blood tests measure specific biological markers that reflect more recent drinking behaviour or changes in liver function.

Several blood biomarkers may be analysed depending on the purpose of the assessment, with the most commonly requested including Liver Function Tests (LFTs), Carbohydrate Deficient Transferrin (CDT) and, where appropriate, a Full Blood Count (FBC).

Liver Function Tests (LFTs) measure a range of enzymes and proteins produced by the liver. Abnormal results may indicate liver inflammation or damage, which can occur for a variety of medical reasons, including sustained excessive alcohol consumption. Laboratories typically assess a panel of markers such as Alanine Aminotransferase (ALT), Aspartate Aminotransferase (AST), Alkaline Phosphatase (ALP), Gamma-Glutamyl Transferase (GGT) and bilirubin to provide a comprehensive assessment of liver health.

Carbohydrate Deficient Transferrin (CDT) is a well-established biomarker associated with chronic excessive alcohol consumption. Regular heavy drinking can lead to elevated CDT concentrations, making it a useful indicator when assessing prolonged alcohol misuse. CDT typically reflects alcohol consumption over the previous two to four weeks, complementing the longer detection window provided by hair alcohol testing.

A Full Blood Count (FBC) may also be requested alongside other blood biomarkers. Although it is not a direct test for alcohol consumption, excessive long-term alcohol intake can affect the production and appearance of blood cells. When interpreted alongside CDT, LFTs and other clinical information, an FBC can provide additional evidence to support an overall assessment.

Because each blood biomarker measures a different physiological response to alcohol, no single blood test should be interpreted in isolation. In many legal and clinical cases, laboratories recommend combining blood alcohol testing with hair alcohol testing to provide a more comprehensive assessment of alcohol consumption. Blood biomarkers such as CDT, LFTs and FBC provide valuable information about recent alcohol use and its effects on the body, while hair alcohol testing provides evidence of longer-term drinking behaviour. Accredited laboratories interpret these results alongside the individual's medical history, declared alcohol consumption and the reason for testing before reaching an overall conclusion.

Blood alcohol testing - PEth

Phosphatidylethanol (PEth) is regarded as one of the most specific and sensitive direct biomarkers of alcohol consumption currently available. Unlike indirect biomarkers such as CDT or LFTs, PEth forms only in the presence of ethanol, meaning a positive result provides strong evidence that alcohol has been consumed.

PEth is produced within the membranes of red blood cells after alcohol is consumed and remains detectable in the bloodstream for approximately one month, making it particularly useful for assessing recent alcohol consumption, monitoring abstinence and distinguishing between low, moderate and heavy drinking patterns.

One of the major advantages of PEth testing is that the result is not significantly influenced by age, gender or previous alcohol dependency, providing a highly reliable indicator of alcohol intake during its detection window. This makes PEth increasingly valuable for family court proceedings, child safeguarding cases, workplace investigations and clinical monitoring where objective evidence of recent alcohol consumption is required.

Although PEth provides excellent information about recent drinking behaviour, it does not assess alcohol consumption over several months. For this reason, many laboratories recommend combining PEth blood testing with hair alcohol testing, allowing both recent and longer-term alcohol consumption to be assessed using complementary biomarkers. This combined approach is widely regarded as the most comprehensive method of evaluating alcohol consumption.