Ethyl glucuronide in keratinous matrices as biomarker of alcohol use: A correlation study between hair and nails.

To quantify alcohol use, objective, specific and sensitive long-term alcohol markers are necessary. Ethyl glucuronide (EtG), a direct metabolite of alcohol, accumulates in keratinous matrices such as hair and nails, and is a specific and sensitive long-term biomarker for the detection of chronic alcohol consumption. So far, research has primarily focused on the detection of EtG in hair, and studies on its measurement in nails are scarce. In this article, we assessed EtG concentrations in hair, finger- and toenails from the same individuals in order to evaluate the direct correlation between the matrices. To this end, a total amount of 45 hair, 41 fingernail, and 13 toenail samples were collected from patients treated for alcohol use disorders at two psychiatric centers in Belgium. Samples were analyzed by gas chromatography-tandem mass spectrometry. Hair EtG concentrations ranged from <LLOQ to 1149pg/mg (median=164pg/mg, IQR [42; 283]). Fingernail EtG concentrations ranged from <LLOQ to 4090pg/mg (median=250pg/mg, IQR [74; 645]). Toenail EtG concentrations ranged from 127 to 3792pg/mg (median=687pg/mg, IQR [379; 1370]). EtG levels in hair and nails were significantly and positively correlated (p-values<0.001, r=0.70 and r=0.62, respectively). Higher concentrations were present in finger- and toenails compared to hair, which might be attributed to the slower growth rate of nails, resulting in increased accumulation of EtG. Hence, nail analysis may be interesting when low concentrations of EtG are expected, e.g. to discriminate between teetotalers and social drinkers. In addition, the current study proposes preliminary cut-off values for EtG concentrations in fingernails: >123pg/mg for chronic excessive alcohol consumption, 59-123pg/mg for moderate alcohol consumption, and <59pg/mg for alcohol abstinence. In light of these results, nails may be a useful alternative to hair samples for monitoring of long-term alcohol consumption, e.g., in cases where hair is not available. Further studies are needed to establish cut-off values for EtG levels in nails.