GHB in postmortem toxicology. Discrimination between endogenous production from exposure using multiple specimens.

Since gamma-hydroxybutyrate (GHB) is present in both blood and urine of the general population as an endogenous compound, toxicologists must be able to discriminate between these endogenous levels and a concentration resulting from exogenous exposure. The implementation of a cut-off concentration must be done cautiously, due to the wide distribution of endogenous concentrations. To verify the accuracy of a proposed 50 mg/l postmortem blood cut-off, we tested 71 autopsy cases of subjects where the cause of death could exclude GHB exposure. The delay between death and autopsy ranged from 12 to 72 h. GHB was tested by gas chromatography-mass spectrometry (GC-MS) after precipitation. Briefly, 20 microl of blood, bile, or vitreous humor was pipetted in a glass tube, followed by 20 microl of GHB-d6 and 45 microl of acetonitrile. After vortexing and centrifugation, the supernatant was collected and evaporated to dryness. The residue was derivatized with bis(trimethylsilyl)trifluoroacetamide (BSTFA) with 1% trimethylchlorosilane (TMCS) for 20 min at 70 degrees C. After injection on a 30 m HP5 MS capillary column, GHB (m/z 233, 204, and 147) and GHB-d6 (m/z 239) were identified by MS. GHB tested positive in all the 71 whole blood (cardiac) specimens, with concentrations in the range 0.4-409 mg/l, with a major distribution in the range 10-40 mg/l. A concentration >50 mg/l was observed in 14 cases. As there was no data to support GHB exposure, this was considered as postmortem formation. In order to discriminate this contamination, when available, femoral blood, bile or/and, vitreous humor were tested. The following results were obtained: cardiac blood (55-409 mg/l) versus bile (6.1-238 mg/l) in seven cases; cardiac blood (51-409 mg/l) versus femoral blood (17-44 mg/l) in five cases, and cardiac blood (51-409 mg/l) versus vitreous humor (3.9-2 mg/l) in six cases. It is obvious that bile does not fit the requirements for discrimination and that femoral blood and mostly vitreous humor can be of particular interest. These results demonstrate that a positive (>50 mg/l) postmortem blood GHB concentration cannot support alone drug exposure and that it is essential to document the case with other specimens, including peripheral blood and vitreous humor.