Endogenous concentrations of GHB in postmortem blood from deaths unrelated to GHB use

Gamma-hydroxybutyrate (GHB) is an endogenous compound, but its presence in postmortem blood presents a challenge when interpreting elevated levels as GHB is misused as a recreational drug and is also produced postmortem. A total of 387 postmortem cases (273 male and 114 female) submitted to the toxicology laboratory between 2010 and 2012 specifically requested the analysis of the ketoacidosis biomarker, beta-hydroxybutyrate (BHB). No reference to GHB use was identified in any of the case files; however, BHB and GHB are measured simultaneously using deuterated GHB as the internal standard (GHB-d6) within a calibration range of 5–500 mg/L. GHB was not detected or <10 mg/L in 18% of the cases (n = 68), between 10 and 50 mg/L in 73% of the cases (n = 283) and between 51 and 193 mg/L in 9% of the cases (n = 36). The manner of death was classified as accidental (n = 11), alcohol-related (n = 237), drug-related (n = 23), homicide (n = 1), natural (n = 91), suicide (n = 9), medical-related (n = 1) and undetermined (n = 14). Six cases had GHB concentrations in excess of 100 mg/L with advanced decomposition changes noted in five of these cases. Moderate-to-advanced decomposition was also noted in 50% (n = 15) of the cases with GHB concentrations in excess of 50 mg/L but <100 mg/L. Approximately one-third of the blood samples tested contained a preservative and although a higher proportion of these samples had GHB concentrations <10 mg/L or not detected (∼30% preserved versus 11% unpreserved), there were still cases with GHB concentrations >51 mg/L (∼6% preserved versus 11% unpreserved). This study highlights the danger of only using a cutoff to establish endogenous levels compared with exogenous use of GHB in postmortem blood.