Phosphatidylethanol as an outcome measure in treatment aimed at controlled drinking

Background: Phosphatidylethanol (PEth) is a specific marker of alcohol intake, which can be used both as a screening method for harmful drinking, and as an outcome measure in the treatment of alcohol use disorder (AUD). However, it is still unclear what cut-off values to use as indicating risky levels of alcohol use in a treatment setting. We therefore aimed to investigate the correlation between PEth and self-reported drinking over the course of treatment, and identify the optimal cut-off for risky drinking, for patients with AUD and a stated goal of controlled drinking.
 
Methods: We used data from a randomized controlled trial (n=250) of two different psychological treatments aiming for controlled drinking, conducted in a specialized addiction treatment center in Stockholm, Sweden. Outcomes were measured at five different time points over the course of two years of follow-up. PEth values were correlated with subjective reports of recent drinking based on the Timeline Follow-Back method, and with other biomarkers (CDT, GGT).
 
Results: The correlation between PEth and self-reported alcohol intake increased significantly over time, with the weakest correlation found at baseline (Spearman’s ρ=0.42) and the strongest at two years follow-up (ρ=0.69). PEth values correlated moderately with other alcohol biomarkers. When used to indicate risky drinking (≥10 units per week), receiver operating characteristic analysis revealed PEth≥0.22 μmol/l to be the optimal cut-off.
 
Conclusions: PEth is a useful outcome measure in the treatment of AUD, that can be used to validate subjective reports of current drinking. In a treatment setting aimed at controlled drinking, the accuracy of self-report measures seems to improve over time, and self-reports correlate strongly with objective markers at long-term follow-up. In this context, a PEth value of ≥0.22 μmol/l is a sensitive and quite specific indicator of risky drinking.