Biotin-Phosphatidylethanol (Biotin-PEth) can be used to build biological assays testing for serum and in vitro PEth levels. PEth is formed primarily by transphosphatidylation of phosphatidylcholine (PC) by phospholipase D. Most PEth (about 75%) is incorporated into erythrocyte membranes, and is one of the longest-lived circulating ethanol metabolite yet identified.