Gamma-hydroxybutyrate in urine and serum: additional data supporting current cut-off recommendations

Besides the use of Gamma-Hydroxybutyrate (GHB) as a recreational drug, use of GHB as an agent in drug-facilitated crime should also be considered. In these cases, there is often a delay of several hours from the incident to collection of the samples. As GHB has a very short plasma half-life, the window of detection is small and in the majority of these specimens, levels of GHB are low. Because GHB is naturally occurring in humans, discrimination between endogenous and exogenous GHB is complicated, particularly in those samples with low concentrations. In this study, endogenous GHB levels of 50 serum and 50 urine samples were determined by GC-MS after conversion to trimethyl-silyl-derivatives. Concentrations in serum ranged from 0.62 to 3.24 mg/L (mean=1.14 mg/L; median=0.97 mg/L) and from 0.64 to 4.20mg/L (mean=1.21 mg/L; median=0.96 mg/L) in urine. Based on this substantial data, the current suggested lower cut-off of 4 mg/L in ante mortem serum samples could be confirmed. For urine, we propose the lower cut-off of 6 mg/L instead of 10mg/L to avoid false negative interpretation.