What it measures
Phosphatidylethanol (PEth) forms in the membranes of red blood cells only when alcohol is present. It builds up with regular drinking and clears over a few weeks, so the result reflects drinking over the past few weeks.
Why people test it
- Used to show alcohol use over the past few weeks, as it forms only when alcohol is present.
- Asked for in some workplace, legal and family court assessments of drinking.
- Used to confirm not drinking, for example in a recovery or monitoring programme.
- Repeated over time to follow a change in drinking.
Typical range
Labs report PEth in ng/mL against their own cut-offs, which vary by lab, method, age and sex. Your report shows the lab's own range.
Finger-prick or vein?
Finger-prick and vein samples are both offered. PEth sits in red cells, so it is measured in whole blood, and finger-prick blood spots are suitable.