Hair EtG: Alterations in segment levels accompanying hair growth.

Hair levels of the direct ethanol biomarker ethyl glucuronide (EtG) are used to evaluate history of alcohol intake. The proximal 3 cm of the hair sample is most often analyzed and this is assumed to represent the intake of ethanol over approximately the past three months. The aim of this study was to investigate change of EtG levels during hair growth in an ethanol-abstinent period. Twenty-seven patients were recruited from an alcohol treatment clinic. A hair sample was collected after hospitalization and EtG was analyzed in the 0-3 cm hair segment (T1). Another hair sample was collected after one month of abstinence and EtG was analyzed in the 1-4 cm hair segment (T2), discarding the proximal 1 cm (0-1 cm) of the segment. As a result of the segment choice and assuming a hair growth rate of 1 cm per month, T2 should represent roughly the same time of alcohol exposure as segment T1. The median concentration of EtG in T1 was 100 pg/mg (range 7.7-1320) and the median concentration in T2 was 53.4 pg/mg (range < LOQ-692). EtG concentrations decreased significantly from T1 to T2 (p = 0.003) and the median change in EtG from T1 to T2 was -46.0%. This study shows decreasing EtG concentrations in most subjects in a hair segment during growth when comparing two segments that is assumed to represent roughly the same period of alcohol intake. Further research is needed to confirm if this observed decline of EtG is a result of wash-out-effects of EtG or other factors.