Effect of the analyzed hair length on fatty acid ethyl ester (FAEE) concentrations in hair--is there congruence of cut-offs for 0-3 and 0-6 cm hair segments?

Background: According to the current SoHT consensus for the use of alcohol markers in hair FAEEs can be analyzed in the proximal 0-3 or 0-6 cm segment with the cut-offs 0.2 and 0.4 ng/mg for abstinence assessment and 0.5 and 1.0 ng/mg for chronic excessive alcohol consumption. Both sets of cut-offs should be congruent for uniform interpretation.

Methods: FAEEs were determined in parallel for the 0-3 and the 0-6 cm segment of 157 hair samples and the concentration ratio between both segments (0-3 cm)/(0-6 cm) was calculated. For comparison, EtG was measured in the 0-3 cm segment of 135 of these samples and the FAEE concentration ratio was calculated by re-evaluation of segmental concentrations from further 42 samples of a previous study.

Results: The concentration ratio ranged from 0.3 to 1.5 (mean 0.83, median 0.82) and showed that the current cut-offs (ratio 0.50) are not congruent and that the cut-offs of the 0-3 cm are more restrictive against alcohol use or abuse. There was no correlation between the ratio and the concentration of FAEEs or EtG showing that the ratio does not depend on the drinking amount. Furthermore, no significant difference of the ratio was found between cosmetically untreated, bleached, dyed or spayed hair samples. Adaptation of the 0-3 cm cut-offs by increasing to 0.3 and 0.8 ng/mg respectively improved the congruence of both segment lengths but did not lead to a better agreement between FAEE and EtG interpretation.

Conclusions: It follows from the results and further literature data that the variable length of the proximal hair segment between 3 and 6 cm which is possible according to the present SoHT consensus additionally contributes to the uncertainty of interpretation caused by biological variability and hair cosmetics. Furthermore, it is improbable from the present state of knowledge that a proximal segment length above 3 cm unambiguously enables the detection of alcohol consumption or abuse occurring more than 3 months before sampling. Therefore, it should be considered in a future consensus to redefine the hair length for both markers on 0-3 cm.