Ethyl glucuronide in hair and fingernails as a long-term alcohol biomarker

AIMS This study aimed to evaluate the performance of ethyl glucuronide (EtG) in hair and fingernails as a long-term alcohol biomarker. DESIGN Cross-sectional survey with probability sampling. SETTING Midwestern United States. PARTICIPANTS Participants were 606 undergraduate college students between the ages of 18 and 25 years at the time of selection for potential study participation. MEASUREMENTS EtG concentrations in hair and fingernails were measured by liquid chromatography-tandem mass spectrometry at three thresholds [30 picograms (pg) per milligram (mg); 20 pg/mg; and 8 pg/mg]. Any weekly alcohol use, increasing-risk drinking and high-risk drinking on average during the past 12 weeks was assessed by participant interview using the time-line follow-back method. FINDINGS In both hair and fingernails at all three EtG thresholds, sensitivity was greatest for the high-risk drinking group [hair: 0.43, confidence interval (CI)=0.17, 0.69 at 30 pg/mg, 0.71, CI=0.47, 0.95 at 20 pg/mg; 0.93, CI=0.79, 1.00 at 8 pg/mg; fingernails: 1.00, CI=1.00-1.00 at 30, 20 and 8 pg/mg] and specificity was greatest for any alcohol use (hair: 1.00, CI=1.00, 1.00 at 30 and 20 pg/mg; 0.97, CI=0.92-0.99 at 8 pg/mg; fingernails: 1.00, CI=1.00-1.00 at 30, 20 and 8 pg/mg). Areas under the receiver operating characteristic curves were significantly higher for EtG concentration in fingernails than hair for any weekly alcohol use (P = 0.02, DeLong test, two-tailed) and increasing-risk drinking (P = 0.02, DeLong test, two-tailed). CONCLUSIONS Ethyl glucuronide, especially in fingernails, may have potential as a quantitative indicator of alcohol use.