How much alcohol is needed to test positive for PEth?

Because phosphatidylethanol (PEth) is a direct biomarker of alcohol, it is the most accurate blood test to determine alcohol abuse.

But how much alcohol is needed to test positive for PEth? The quantity of alcohol consumed affects PEth in a fairly straightforward manner. High levels of alcohol consumption produce high concentrations of PEth. Low alcohol consumption leads to low PEth concentrations.

Drinking experiments show that PEth can be detected in blood after 1–2 hours following a single drinking episode. This PEth detection can also last for up to 12 days. PEth production begins as soon as ethanol is consumed and peaks within 8 h after alcohol ingestion. Once formed, it degrades very slowly, which is important for its use as an alcohol biomarker.

In addition, PEth can clearly distinguish daily alcohol consumption of more than 60 g ethanol from lower alcohol consumption. One unit of alcohol is defined as 8 g of pure alcohol. As a comparison, the other blood alcohol tests of MCV (mean corpuscular volume), carbohydrate‐deficient transferrin (CDT) and liver function tests (LFT) generally require the daily consumption of over 60 g/day of alcohol over several weeks to cause clinically significant elevations. This means that PEth testing can detect chronic as well as single-drinking episodes.

Related: PEth vs. EtG Testing

The table below shows the range of PEth levels that can be measured in blood alcohol testing.

PEth level < 10 µg/L Abstinence or very low alcohol consumption in the past month.
PEth level 10–35 µg/L Low/occasional alcohol consumption in the past month.
PEth level 35–210 µg/L PEth level 35–210 µg/L Social/moderate alcohol consumption in the past month.
PEth level > 210 µg/L Excessive alcohol consumption in the past month.

In terms of all alcohol tests, PEth is second to the detection of ethyl glucuronide (EtG  – another direct metabolite of ethanol) in hair alcohol testing. However, PEth analysis has the advantage of allowing faster verification as to whether an individual has changed their drinking behaviour.


Last reviewed: 05/19/2023


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