Endogenous concentrations of gamma-hydroxybutyrate (GHB) in post-mortem blood from deaths unrelated to GHB Use

Introduction
Gamma-hydroxybutyrate (GHB) is an endogenous compound but its presence in post-mortem blood presents a challenge when interpreting levels as it is misused recreationally, but is also produced postmortem. The use of preservatives has been suggested to minimize this production and Kintz and Villain have also suggested the use of a cut-off of 50 mg/L for post-mortem blood samples to differentiate between post-mortem production and exogenous GHB use. This is of particular importance when other matrices are unavailable or decomposition has advanced. This study presents the largest data set of post-mortem cases where exogenous GHB use was excluded, decomposition changes were noted and samples were submitted for analysis in both preserved and unpreserved vials.

Objective
The aim of this retrospective study was to evaluate the concentrations of GHB found in post-mortem cases where alcoholic and/or diabetic ketoacidosis was suspected, with special focus on the relationship between GHB concentration and the advancement of decomposition.

Method
GHB was analysed using deuterated GHB as the internal standard (GHB-d6) within a calibration range of 5 - 500 mg/L. The analytical method was adapted from a method developed by Hassan and Cooper. Only cases submitted for analysis between 2010 and 2012 for investigations into the potential role of ketoacidosis were selected. Additional details, including age, sex, cause and manner of death, date of death, the last time the deceased was seen alive and the date of the autopsy were collated.

Results
A total of 387 post-mortem cases (273 male, 114 female) were submitted to the laboratory between 2010 and 2012 specifically requesting tests for suspected ketoacidosis. GHB was not detected at or below 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), drugrelated (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 less than 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 v 11% unpreserved), there were still cases with GHB concentrations > 51 mg/L (~6% preserved v 11% unpreserved).

Conclusion
The findings in this study support other published investigations highlighting the difficulties and dangers of only using a cut-off to establish endogenous levels compared with exogenous use of GHB in postmortem blood, especially when decomposition has reached advanced stages. The use of a preservative may be advantageous but more research must be conducted.