A limitation of our study is that there is a gap in time between when AUDIT-C was measured (2005-2007) and when the PEth and ADH1B samples were collected (2007-2016). Similarly, the long-term stability of PEth in frozen blood samples is unknown. Faller et al found no assay loss in samples stored for 30 days at -80C(Faller et al., 2013). We would expect that any bias introduced by the gap between AUDIT-C and sample collection, or possible sample degradation while in storage, would be toward the null. However, we found strong associations between PEth and all three AUDIT-C metrics, similar to those reported by Piano et al(Piano et al., 2015) from samples not subject to lengthy storage. Thus we find the consistency of biomarker results and self- report reassuring. ADH1B genotype does not change over time, so the difference in time between EHR AUDIT-C and ADH1B genotype is not relevant.
