Endogenous GHB in Segmented Hair Part I: Inter-individual Variation for Group Comparisons

Abstract

Abstract While earlier studies have attempted to resolve the challenges encountered when interpreting gamma-hydroxybutyric acid (GHB) concentrations in hair (primarily due to its endogenous presence), few have had large sample sizes. The first objective of this study was to evaluate the inter-individual variation of endogenous GHB concentrations. The second objective, to be detailed in another report, was to assess intra-individual variation and the impact on exogenous GHB discrimination. Over 2,000 hair segments from 141 women and 73 men (all processed hair 3–12 cm long) were analyzed in this study. The raw calculated range of endogenous GHB concentrations was <0.40–5.47 ng/mg with 97.5% of the segmental results calculated less than 2.00 ng/mg. Imputation, assuming a lognormal distribution, was applied to the data to include non-detect (ND) data (<LOQ), which led to an estimated endogenous GHB range of 0.16–5.47 ng/mg. Kruskal–Wallis tests were employed on a segmental basis for group comparisons. This test was applied to the male and female segmental medians and subsequently indicated that these groups were different at the α = 0.05 level of significance. Additionally, female hair samples appeared to have a trend comprising higher endogenous GHB concentrations close to the scalp and a mean net decrease of ~0.2–0.3 ng/mg distally. Male hair samples displayed the opposite trend, with a mean net increase of ~0.5–0.6 ng/mg from the proximal to the distal end of the hair shaft. It was also concluded that differences exist between the median GHB concentrations of the ‘treated’ and ‘untreated’ hair in the female group at the α = 0.05 level of significance. Age groups and races were analyzed, but none of the observed differences in median concentration were significant at α = 0.05. This is the largest endogenous GHB hair population study to date and provides substantial new data on inter-individual variation and chronological trends of GHB concentrations in hair.