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PEth vs EtG Testing

Marie Law Alphabiolabs

By Marie Law, Head of Toxicology at AlphaBiolabs
Last reviewed: 29/09/2023

In courts across the UK, legal professionals are using blood alcohol testing as an essential part of the evidential picture, allowing courts to gain valuable insight into a client’s alcohol consumption.

In cases where the safeguarding of children and vulnerable people is paramount, such tests provide a rich source of information, enabling local authorities to act on urgent welfare needs.  

But when it comes to blood alcohol tests, not all are created equal, with Phosphatidylethanol (PEth) testing providing the most conclusive insight into a person’s drinking patterns.

In this article, we discuss what you need to know about Phosphatidylethanol (PEth) testing and how this – combined with EtG and EtPa hair alcohol testing – can provide the most conclusive insight into an individual’s drinking behaviour.

Table of contents
  • What is PEth blood alcohol testing?
  • How can blood alcohol levels be measured using PEth testing?
  • What is EtG hair alcohol testing?
  • Can you use body hair for an EtG hair alcohol test?
  • What makes PEth blood alcohol testing so conclusive?
  • How does PEth blood alcohol testing compare to EtG and EtPa hair testing?
  • Can you test nail clippings for the presence of EtG?
  • Which alcohol test is best for my client – PEth testing or EtG testing?
  • Where can I order an alcohol test for court?

What is PEth blood alcohol testing?

AlphaBiolabs offers four types of legally-instructed blood alcohol test to determine an individual’s level of alcohol consumption:

A Phosphatidylethanol test – also known as a PEth test – looks for the presence of PEth, a direct biomarker of alcohol, in a blood sample.

An abnormal phospholipid, PEth requires ethanol (the intoxicating agent in alcoholic drinks) for its production. This means that it is only present in the body when alcohol has been consumed.

A PEth test can provide an overview of historic alcohol consumption of up to four weeks, and can be used to detect both chronic and single-drinking episodes.

How can blood alcohol levels be measured using PEth testing?

Drinking experiments show that Phosphatidylethanol (PEth) can be detected in blood after 1-2 hours and for up to 12 days after a single drinking episode.

Additionally, daily alcohol consumption of more than 60g of ethanol can be clearly distinguished from lower alcohol consumption.

This means that PEth testing can detect chronic and single-drinking episodes. It can also be used to monitor abstinence, drinking behaviour, identify relapse, and verify whether an individual has changed their pattern of alcohol consumption.

The table below shows the range of PEth levels that can be measured using an AlphaBiolabs’ blood alcohol PEth test.

PEth level (ng/ml)
< 20 Abstinence or low alcohol consumption in the past month prior to sample collection
20-210 Social/moderate alcohol consumption in the past month prior to sample collection
> 210 Excessive alcohol consumption in the past month prior to sample collection

What is EtG hair alcohol testing?

Ethyl glucuronide (EtG) is a specific biomarker of alcohol, and one of two alcohol biomarkers that we test for in head hair at AlphaBiolabs: the other being ethyl palmitate (EtPa), which is a fatty acid ethyl ester (FAEE).

Because EtG is a direct metabolite of ethanol, the intoxicating agent in alcoholic drinks, it can only be found in the hair when alcohol has been consumed. This makes EtG testing the most reliable form of hair alcohol testing for determining an individual’s level of alcohol consumption.

Both EtG and EtPa are incorporated into the hair in different ways when alcohol is consumed: EtG via sweat, and EtPa via sebum, an oily substance secreted by glands in the scalp.

EtG is water soluble, produced in the liver and can be impacted by various hair treatments including bleaching, perming, dyeing, straightening and excessive washing.

EtPa is formed in the sebaceous glands from ethanol diffusing from the blood circulation and then deposited into hair primarily from sebum (from the oil glands on the scalp). EtPa is lipophilic so while not water soluble, its presence can be affected by the use of hair products that contain alcohol, such as sprays, gels, and wax.

Because of their respective strengths and weaknesses, AlphaBiolabs always recommends that EtG and EtPA hair alcohol tests be performed together, for the most conclusive insight into an individual’s level of alcohol consumption.

Both EtG hair testing and EtPa hair testing can provide a three- or six-month overview of alcohol consumption.

Can you use body hair for an EtG hair alcohol test?

If head hair is unavailable, body hair can be used to test for the presence of ethyl glucuronide (EtG).

However, due to the way in which ethyl palmitate (EtPa) is incorporated into hair, body hair can only be used to test for EtG, not EtPa.

Due to the rate at which body hair grows, the time period would also be more approximate, with body hair (arm, chest, leg, beard) providing us with up to a 12-month overview of alcohol use.

When testing body hair for the presence of EtG, we also recommend blood alcohol testing (e.g. PEth testing) – as offered by AlphaBiolabs – in conjunction with a clinical assessment sourced from elsewhere, to gain a greater insight into an individual’s alcohol consumption.

What makes PEth blood alcohol testing so conclusive?

There are four main types of blood alcohol testing that legal professionals can call upon for supporting evidence in a case – all of which can provide a four-week historic overview of alcohol use:

Unlike CDT, LFT and MCV – all of which are indirect biomarkers of alcohol, whose presence can be affected by pre-existing medical conditions and medications, among other factors – PEth is a direct biomarker of alcohol.

An abnormal phospholipid, it requires ethanol for its production, meaning that it is only present in the body when alcohol has been consumed.

PEth production begins as soon as ethanol is consumed and accumulates in the blood with frequent alcohol consumption, giving it a high specificity (48-89 per cent) and sensitivity (88-100 per cent).

Drinking experiments show that PEth can be detected in blood after one to two hours, and for up to 12 days after a single drinking episode.

In addition, daily alcohol consumption of more than 60g of ethanol (7.5 units) can clearly be distinguished from lower alcohol consumption, meaning that PEth testing can be used to detect chronic and single-drinking episodes.

The wealth of information provided by a PEth test, alongside its conclusiveness, is what makes it the most essential of all blood alcohol tests, enabling us to monitor abstinence, drinking behaviour, or identify relapse.

PEth analysis is also the only blood alcohol test that can be undertaken during pregnancy or within two months of the birth.

How does PEth blood alcohol testing compare to EtG and EtPa hair testing?

PEth is second only to the detection of ethyl glucuronide (EtG) and ethyl palmitate (EtPa), a fatty acid ethyl ester (FAEE), in the hair.

Both EtG and EtPa are biomarkers of alcohol and give us a highly accurate insight into patterns of drinking, with a three- or six-month overview of usage.

Each is absorbed into the hair via different routes, and their levels can assist in assessing excessive alcohol consumption.

EtG is water soluble, produced in the liver and can be impacted by various hair treatments including excessive washing.

EtPa is formed in the sebaceous glands from ethanol diffusing from the blood circulation and then deposited into hair primarily from sebum (from the oil glands on the scalp). EtPa (FAEE) is lipophilic so while not water soluble, its presence can be affected using alcohol-containing hair products such as sprays, gels, and wax.

Because of their respective strengths and weaknesses, both EtG and EtPA tests should be performed together, and their findings used to support each other, as shown in LB Richmond v B & W & B & CB [2010] EWHC (2903) Fam, where Mr Justice Moylan gave guidance on the evidential worth of hair strand testing.

Within this guidance, it was also stressed that hair strand tests/hair alcohol tests should not be used in isolation to reach evidential conclusions.

By performing these tests in conjunction with PEth and other blood tests, a more holistic conclusion can be drawn as to a person’s alcohol use.

Can you test nail clippings for the presence of EtG?

Yes, it is possible to use fingernails or toenails to detect the presence of ethyl glucuronide (EtG), a direct biomarker of alcohol, in a nail clipping sample.

When a person consumes alcohol, it is processed by the liver, and its metabolites (including EtG) are released into the bloodstream.

As the nail grows, substances pass from the blood vessels below the nail and into the nails themselves. EtG biomarkers become trapped along the length of the nail fibres and can be identified via laboratory testing.

Nail alcohol testing can provide an overview of up to 12 months – six months for fingernail clippings, and 12 months for toenail clippings. This is because fingernails and toenails grow at different rates.

However, it’s important to note that nail alcohol testing can only be used to establish whether a person has remained abstinent. It cannot be used to identify chronic or single-drinking episodes.

As with body hair alcohol testing, because nail alcohol testing can only be used to detect the presence of EtG, we always recommend that nail alcohol/nail EtG testing be done in conjunction with a blood test (e.g. PEth) – as offered by AlphaBiolabs – and a clinical assessment sourced elsewhere, to gain a more conclusive insight into an individual’s alcohol use.

Which alcohol test is best for my client – PEth testing or EtG testing?

Which alcohol test you choose, and which test is best for your client, can vary, depending on the circumstances of the case and which tests have been ordered by the court.

However, we would always advise that blood alcohol testing combined with hair testing provides the fullest picture from which to draw conclusions about an individual’s level of alcohol consumption.

This is especially important in family cases, where safeguarding children and vulnerable people is the highest priority.

The table below outlines what blood, hair and nail alcohol testing can tell us about a person’s historic alcohol consumption.

Purpose PEth EtG in head hair EtG in body hair EtG in nails
Abstinence
Social drinker
Chronic and excessive drinker
Recent use (hours)
Recent use (days)
Window of detection (up to) 4 weeks 3 or 6 months* 12 months* 12 months*

*Overview

Where can I order an alcohol test for court?

Using highly accurate scientific analysis in the form of PEth blood testing and EtG hair testing and examining the way in which the body absorbs alcohol, a case can be made to protect those in need – and reunite families where abstinence has been achieved.

AlphaBiolabs has extensive experience working with family law professionals, social workers, local authorities, and Family Court, providing a range of legal testing services including legal alcohol testing.

It’s easy to request a quote for legally instructed alcohol testing online now.

Alternatively, call our Legal sales team on 0333 600 1300 or email testing@alphabiolabs.com and a member of the team will be in touch to discuss your case.

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Marie Law

Marie Law

Head of Toxicology at AlphaBiolabs

A highly-skilled and respected scientist with over 13 years’ experience in the field of forensics, Marie joined AlphaBiolabs in 2022 and oversees the company’s growing toxicology team.

As Head of Toxicology, Marie’s day-to-day responsibilities include maintaining the highest quality testing standards for toxicology and further enhancing AlphaBiolabs’ drug and alcohol testing services for members of the public, the legal sector, and the workplace sector.

Prior to joining AlphaBiolabs, Marie held roles with LGC Forensics, Cheshire Constabulary and Eurofins Forensic Services.

As DNA Business Unit Manager at Eurofins, Marie successfully oversaw the relocation and merger of two separate laboratories, improving turnaround times and performance.

While working as Quality and Performance Manager at Cheshire Constabulary, Marie was responsible for managing accreditations for 15 forensic units, securing several new accreditations for the force, including for digital forensics and fingerprinting.

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