Alcohol markers in hair: an issue of interpretation

Ethyl glucuronide (EtG) and fatty acid ethyl esters (FAEEs) are metabolites of alcohol that when detected in hair can provide evidence of a person's drinking behavior. The analysis of these compounds in hair has become commonplace in recent years and has been used as evidence in legal proceedings. Despite the routine use of such toxicological analysis, the correct interpretation of alcohol biomarker hair testing can be complex, and there may be debate as to the significance of the data. This paper considers whether the accepted norm of applying interpretative cut-off values to EtG and FAEE concentrations from hair samples is appropriate, and asks whether Bayesian theory, using a likelihood ratio approach may offer greater insight as to the strength of evidence. In addition to the complexity of result interpretation in this field, the sensitivity of alcohol biomarkers in hair to distinguish low level drinking from abstinence also represents a significant challenge. The use of fingernail EtG testing as an alternative to hair analysis is explored in this paper and it is proposed that fingernails may in theory show a higher uptake of EtG than hair, and thus show potential as a useful alternative matrix to document long-term low to moderate alcohol consumption.