Long-term stability of GHB in post-mortem samples and samples from living persons, stored at -20°C, using fluoride preservatives

PURPOSE

Reanalyses are frequently requested in forensic toxicology, and knowledge of the stability of drugs in biological samples is of major importance for the interpretation of the toxicological findings. Currently, the literature on stability of gammahydroxybutyrate (GHB) in blood samples from living subjects and in post-mortem blood is limited. The purpose of this study was to evaluate the long-term stability of GHB in both blood samples from persons suspected of drug use and post-mortem blood samples.

METHODS

A total of 59 reanalyses were performed in whole blood samples, 27 samples from living subjects and 32 samples taken at autopsies. The samples were stored in the freezer between 0.4 and 7.2 years at -20°C in vials containing preservatives. Analyses were performed by GC-FID, and cut-off level was 10.3 mg/L. The concentrations in 22 of the samples were below cut-off.

RESULTS

The mean change in concentration between initial analysis and reanalysis was -0.8% for the positive samples from living persons and -7.1% for the positive post-mortem samples. Changes ranged from -32.4% to 21.0% for samples from living and from -30.4% to 34.4% for post-mortem samples. All negative samples were still negative at the time of reanalysis.

CONCLUSION

Reanalysis of these forensic whole blood samples stored several years at -20°C with fluoride preservation did not exhibit changes in GHB concentrations of practical significance for the interpretation of toxicological findings.

In vitro formation of ethanol in autopsy samples containing fluoride ions

We present a case of a death of a diabetic man where the concentration of ethanol in post-mortem blood rose from 0.4 g/l 2 days after autopsy to 3.5 g/l 10 days after autopsy. The presence of fluoride ions in this blood sample was determined with ion chromatography and verified that fluoride ions were added to the vials. The concentrations of free fluoride, corresponding to 0.21 and 0.25% w/v potassium fluoride in blood and urine, respectively, were somewhat lower than the recommended 1% w/v. However, the amount of fluoride ions bound to calcium, proteins and other compounds in the samples is unknown. The blood sample was also subject to microbiological examination, which revealed growth of bacteria. In addition, a very high concentration of glucose was found in vitreous humour from the deceased. To determine whether the ethanol detected at the first analysis was of ante-mortem origin, ethyl glucuronide was analysed. Its absence, in the blood as well as the urine sample, strongly supported the theory that, in this case, all the ethanol detected was formed post-mortem. This case showed that ethanol may be formed in vitro at a very high concentration, despite the verified presence of fluoride ions. Possible reasons for this unusual formation of ethanol were the abundant presence of bacteria, a high level of glucose and, possibly, an insufficient amount of fluoride added to the vials.