The major part of ethylglucuronide (EtG) produced in the liver as a metabolite of alcohol is eliminated in urine. A small fraction is incorporated into the hair matrix. That way hair samples can be analyzed for EtG. According to national and international guidelines (SOHT, EWDTS) a concentration under 7 picogram per milligram hair suggests alcohol abstinence or very low alcohol consumption. An EtG value in hair between 7 and 30 pg/mg can be found in subjects with moderate alcohol consumption and an EtG concentration in hair higher or equal to 30 pg/mg strongly suggests excessive drinking (more than 60 g pure alcohol per day).
In the low risk responsible drinking guidelines of the WHO (World Health Organization) it is recommend that women should not drink more than two drinks a day on average (this corresponds to 16 - 28 g pure alcohol per day) and man, not more than three drinks (24 - 42 g pure alcohol per day).
Depending on the hair length an EtG analysis allows a retrospective detection of alcohol consumption. For example since head hair grows about 1 cm per month, a 3 cm long segment of head hair covers approximately a period of 3 months.