A phosphatidylethanol (PEth) test is the gold standard of blood alcohol tests, which looks for the presence of PEth, an abnormal phospholipid and direct biomarker of alcohol, in a blood sample.

In cases where the safeguarding of children and vulnerable people is paramount, PEth blood alcohol testing provides a rich source of information, enabling family law professionals and authorities to act as needed.

But how much do you really know about PEth testing?

In this blog, we examine some of the most frequently asked questions surrounding PEth alcohol testing, including what the results of the test will show.

What makes PEth blood alcohol testing so conclusive?

Unlike other blood alcohol tests – Carbohydrate Deficient Transferrin (CDT), Liver Function Test (LFT) and Mean Corpuscular Volume (MCV) tests – all of which are indirect biomarkers of alcohol that can be affected by pre-existing medical conditions, medications, and more, PEth is a direct biomarker of alcohol.

This means that PEth requires ethanol (the intoxicating agent in alcoholic drinks) for its production and is only present in the body when alcohol has been consumed, providing the most conclusive insight into a person’s drinking patterns.

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

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 is what makes it the most essential of all blood alcohol tests, enabling us to monitor abstinence, drinking behaviour, or identify relapse. It is also the only blood alcohol test that can be undertaken during pregnancy or within two months of the birth.

When combined with other blood alcohol tests such as Carbohydrate Deficient Transferrin (CDT) testing, Liver Function Test (LFT) and Mean Corpuscular Volume (MCV) test, a thorough bank of evidence can be collated regarding an individual’s alcohol use.

How far do PEth test results go back?

A PEth test can provide an overview of historic alcohol consumption of up to four weeks.

Furthermore, once PEth is formed in the body, it degrades very slowly, making it an extremely reliable indicator of alcohol use.

Experiments have shown that PEth can be detected in a blood sample in as little as one to two hours after a person has consumed alcohol and can remain in the blood for up to 12 days after a single drinking episode.

What will the results show in terms of alcohol consumption?

The results of a PEth blood alcohol test will show the PEth levels that were present in the blood at the time the person’s sample was collected.

PEth accumulates in the blood with more frequent alcohol consumption, making it possible to determine whether a person has consumed alcohol in small/moderate amounts, or whether there has been excessive drinking in the four weeks prior to the blood sample being drawn.

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

AlphaBiolabs offers two types of alcohol test reports: a Certificate of Analysis, which is included as standard and includes a summary of the results, or a Statement of Witness, which is an in-depth report with full analytical results, interpretation, and conclusions, for an additional fee.

While both documents are invaluable for court proceedings, a Statement of Witness provides the most comprehensive interpretation of the findings, including disclosures provided at the time of sample collection (e.g. how much alcohol the donor drinks in a typical week or how long they have been abstinent, if making such a claim).

Court-approved blood alcohol testing from AlphaBiolabs

It’s easy to get a quote for blood alcohol testing online now, direct from our award-winning, accredited laboratory.

Our nationwide network of professional sample collectors are trained to collect a variety of samples under chain of custody, including blood samples for alcohol testing.

We also offer free sample collection for legally-instructed alcohol tests at our Dublin walk-in centre.

For expert advice on which test is best for your case, call our Customer Services team on 01 402 9466 or email testing@alphabiolabs.com and a member of our Legal team will be in touch.

Legal Alcohol Testing

Learn more about our Legal Alcohol Testing services.