[The alcohol biomarker phosphatidylethanol (PEth) - recommendations for use and interpretation of test results]

Phosphatidylethanol (PEth) is a group of phospholipids that are formed in blood from the corresponding phosphatidylcholines in the presence of ethanol by action of phospholipase D. Since PEth formation requires ethanol, it is used as a specific alcohol biomarker. Use of PEth measurement in whole blood as an alcohol biomarker has risen sharply in recent years, increasing the demand for knowledge about how it should be utilized and test results evaluated. In Sweden, the use since 2013 of harmonized LC-MS analytical methods targeting the main form PEth 16:0/18:1, and confirmation of comparable test results between laboratories in the Equalis (Uppsala, Sweden) external quality control program (CV <15%), has enabled use of common decision limits. A measurable PEth result confirms ethanol exposure, but due to interindividual variations in test response to a given dose and elimination half-life during abstinence, it is not possible to indicate the exact amount or time of alcohol intake. However, a PEth level above 0.30 µmol/L (~210 µg/L) is a strong indicator of harmful drinking, while a test result below 0.05 µmol/L (~35 µg/L) excludes harmful drinking but does not confirm complete abstinence. According to current test statistics from two Swedish hospital laboratories, each performing > 60 000 routine PEth measurements annually, ~45-50% of the values were < 0.05 µmol/L, ~23-24% between 0.05-0.30 µmol/L, ~16-19% between 0.30-1.0 µmol/L, and ~10-12% > 1.0 µmol/L. Some PEth results even exceeded 10 µmol/L.