Evidence of seasonal variation of ethyl glucuronide in hair: Modeling a seven-year data series

The assessment of chronic excessive alcohol consumption by ethyl glucuronide (EtG) determination in hair is generally based on a cut-off value of 30 pg/mg recognized by regulatory authorities and scientific societies that guide the decision process. The ongoing debate about the risks connected with the straightforward application of this cut-off refers to the factors that may influence the detected EtG concentration. The present contribution to this debate evaluates the seasonal variation of the averaged EtG values along a seven-year period. Over 65 000 data points have been statistically analyzed to provide a mathematical model that interprets the data, gives insight into several influencing factors, and forecasts progressive data-points of the time series. This model shows that there is an annual pattern in the data exhibiting lower EtG concentrations during warm seasons and higher values in cold seasons. The estimated EtG cycles are characterized by the seasonal variation of ±2.78 pg/mg above and below the overall mean (with 5.56 pg/mg absolute difference overall). This seasonal factor associated with EtG quantification might result in a potential source of bias, at least in the regional/climatic conditions observed in the samples' collection area. Moreover, the EtG time series reveals that the change in the sample pre-treatment procedure has an effect on the modeled pattern as an abrupt increment (+38%) in the mean value of the EtG concentration. This change corresponds to the time when the former protocol of cutting hair into small segments before extraction was substituted by pulverization with a ball mill.