The endogenous presence of gamma-hydroxybutyric acid (GHB) complicates the interpretation of results in cases where an exogenous dosing is suspected. Due to GHB’s rapid metabolism and clearance following exogenous doses, hair has become a preferential matrix for confirmation of GHB exposure in drug-facilitated crimes. However, unlike blood and urine where an agreed-upon cut-off concentration for differentiation between endogenous and exogenous GHB has been made, there has been no consensus on a cut-off concentration for hair. This is due in part to the wide inter- and intra-individual variation that has been observed in endogenous GHB hair studies. A large (>50) population study of 214 donors was conducted to better understand these variations and to evaluate whether a cut-off concentration could be established for endogenous GHB in human hair. As seen in our previous study, the inter-individual variation was large, with concentrations ranging from <0.40 to 5.47 ng/mg. This range made an absolute cut-off concentration recommendation inappropriate, so an alternative approach for GHB discrimination was investigated utilizing the intra-individual variation. Male donors appeared to have greater intra-individual variation than female donors, yet it was noted that segment-to-segment variation along the length of hair had minimal change between individual donor’s adjacent segments. Overall, 97.1% of the adjacent segment differences were within ±0.5 ng/mg. Therefore, instead of a recommended cut-off concentration, it appears that using adjacent segment concentration differences could be a strategy to assist in differentiating endogenous from single exogenous GHB exposure. In the absence of controlled dosing data, previously published segmented results from controlled and suspected dosing donors are examined using the adjacent segmental difference approach and the results compared to currently used ratio-based calculations.

中文翻译：

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分段头发中的内源性GHB第二部分：外源性歧视的个体内部差异。

在怀疑存在外源剂量的情况下，内源性存在的γ-羟基丁酸（GHB）使结果的解释复杂化。由于外源剂量后GHB的快速代谢和清除能力，头发已成为在药物促成犯罪中确认GHB暴露的优先基质。然而，与血液和尿液不同，在血液和尿液中已经确定了用于区分内源性和外源性GHB的临界浓度，在毛发的临界浓度上尚未达成共识。这部分归因于在内源性GHB头发研究中观察到的个体之间和个体之间的广泛差异。进行了一项针对214个供体的大规模（> 50）人口研究，以更好地理解这些变异并评估是否可以为人发中的内源性GHB确定截止浓度。从我们先前的研究中可以看出，个体之间的差异很大，浓度范围从<0.40到5.47 ng / mg。该范围使得绝对临界浓度推荐值不合适，因此利用个体内部差异研究了另一种GHB鉴别方法。雄性供体的个体内部变异似乎大于雌性供体，但是要注意的是，沿着头发长度的节间差异在各个供体的相邻节之间变化很小。总体而言，相邻段差异的97.1％在±0.5 ng / mg以内。因此，代替推荐的临界浓度，似乎使用相邻区段的浓度差异可能是一种有助于区分内源性和单一外源性GHB暴露的策略。