O38: Determination of GHB concentrations in postmortem samples: A case series and comparison between matrices

Abstract

Introduction The interpretation Gamma-HydroxyButyric acid (GHB) concentrations in postmortem samples is a difficult task. Not only is GHB an endogenous substance, but it can also be produced in tissues after death and in vitro in stored samples. Collection of data from forensic cases is important in order to determine a possible threshold value enabling to differentiate between endogenous production and exogenous intake. As multiple analysis on different matrices are also helpful for the interpretation, we compiled a series of forensic cases where peripheral blood, cardiac blood and vitreous humor were analyzed. Methods 31 cases were selected, and analysis were carried out on all available matrices. Delay between death and sampling was unknown for most of the cases and the samples were kept at – 20°C before analysis. One case was a documented user of GHB. In the other cases no GHB intake was evoked in the circumstances of the death. The three matrices (vitreous humor, peripheral blood and cardiac blood) were present for 21 cases and for 10 other cases only two matrices were available (vitreous humor and peripheral blood). GHB was analyzed by gas chromatography- mass spectrometry (GC-MS) after derivation with BSTFA according to a previously published technique (Villain et al., 2003). The limit of quantification was 1 mg/L for all the matrices. Results 82 samples were analyzed, the results are presented in the table below: In peripheral blood, if only the matching pairs of blood samples were considered, mean concentration of GHB was 18,8 mg/L and median was 13,1 mg/L (N = 20). The ratios of the concentrations between the different matrices were evaluated and found as follows: [Cardiac blood]/[Peripheral blood] = 1.9 ; [Vitreous humor]/ [Peripheral Blood] = 0.4. Among the data presented, the alleged user of GHB had the highest concentration in vitreous humor (69 mg/L) and in peripheral blood (246 mg/L). Cardiac blood was not sampled in this case. The ratio between vitreous humor and peripheral blood for this documented abuse of GHB was 0.3. N Mean (mg/L) Median (mg/L) Range (mg/L) Peripheral blood 31 25.1 15.4 Cardiac blood 20 31.2 17.8 Vitreous humor 31 8.1 3.1 1.0 − 69.0 Conclusion Establishing a threshold value for differentiating endogenous production and exogenous intake of GHB is a complex goal. Numerous publications have given concentrations in various matrices. Most of the time the concentrations of GHB between cases with proven intake and cases where no GHB intoxication was suspected are overlapping. Delay between death and sampling, storage conditions and preservatives are some of the multiple factors that could influence the evolution of GHB concentrations over time. With our case series we have shown that the ratio between vitreous humor and peripheral blood is not different for subjects with no history of GHB abuse and intoxicated subjects. This finding needs to be confirmed on larger series of both positive and control cases.