Examining Phosphatidylethanol (PEth) Formation Rates Within and Between Subjects in Ex Vivo Whole Blood

Interpretation of phosphatidylethanol (PEth) is complicated by between-subject variation in the PEth concentrations after matched ethanol exposure. Previous research suggests differences in PEth formation rates may explain this variability but lacks within-subject assessments. This study assesses the extent of variability in PEth formation rates in ex vivo whole blood across a range of ethanol concentrations, with repeated ethanol exposures in blood collected 1 month apart, and the relationship of phosphatidylcholine concentration and PEth formation rate. Whole blood from 10 participants was collected via venipuncture. For each participant, blood was divided into separate samples and incubated with ethanol concentrations ranging 0-236.7 mg/dL at 37°C. Aliquots were removed from each sample every hour for 5 h. PEth 16:0/18:1 concentrations were measured using high performance liquid chromatography with tandem mass spectrometry. PEth formation rates were determined as the slope of linear regressions of PEth concentration over time. The experiment was repeated 1 month later for each participant. The relationship between PEth formation rate and phosphatidylcholine concentration was evaluated with linear regression analysis. PEth formation rate increased with increasing ethanol concentration, with variability between participants, but was consistent within-subject. Different PEth formation rates at the same ethanol concentration were observed in four individuals across two blood collection timepoints. No relationship was observed between phosphatidylcholine concentrations and formation rates, consistent within participants. PEth formation rate varies between individuals and within some individuals. PEth concentrations should be used to monitor an individual's ethanol use over time rather than compared between individuals.