Phosphatidylethanol (PEth) assays were run on dried blood spots created from frozen PBMCs stored at -80C. PEth comprises a group of phospholipids formed from phosphatidylcholine by the action of phospholipase D following the ingestion of alcohol (Helander and Zheng, 2009). PEth can be assayed in whole blood or from dried blood spots using liquid chromatography and mass spectrometry. According to the test lab, the United States Drug Testing Laboratories, Inc. (USDTL), the limit of detection is 2 ng/mL and the lower limit of quantitation is 8 ng/mL. The concentration of PEth is linearly related to the volume of alcohol consumed (Aradottir et al., 2006). A cutoff of 20 ng/mL is used for forensic work and levels >100 ng/mL indicate heavy drinking (J. Jones, USDTL, personal communication). PEth concentrations >500 ng/mL are typically seen in individuals with prolonged heavy drinking (Wurst et al., 2015). Because PEth has a half-life of ∼4 days, it can be assayed in the blood of heavy drinkers for up to 3 weeks after alcohol is consumed (Wurst et al., 2015). The sensitivity of PEth has been
