Assessment of the stability of exogenous gamma hydroxybutyric acid (GHB) in stored blood and urine specimens

OBJECTIVE: The aim of this work is to test the stability of exogenous GHB in whole blood and urine samples collected from living and deceased GHB free-users, spiked with known concentrations of GHB and stored at different temperatures (–20°C, 4°C and 20°C) up to 4 weeks.

MATERIALS AND METHODS: GHB was added to GHB-free ante-mortem blood and urine samples at the concentration of 5 and 10 mg/L, respectively whereas in post-mortem blood and urine specimens at 50 and 10 mg/L respectively. All samples were stored at three different temperatures: –20°C, 4°C and 20°C and extracted and analyzed at three days, 1 week, 2 weeks, 3 and 4 weeks in duplicate. No preservatives were added. GHB was quantified by GC-MS after LLE according to a previously published method.

RESULTS: Post-mortem blood specimens showed a reduction of GHB levels higher than 10% only after a period of 4 weeks of storage for samples kept at +4°C and +20°C, whereas samples stored at –20°C showed a mean reduction of 8.7%. In post-mortem urine samples, there was a mean reduction of GHB levels higher than 20% at all storage temperatures, after 4 weeks of storage. Ante-mortem blood samples showed a reduction of GHB levels lower than 10% only after 3 days of storage at –20°C and at +4°C (samples stored at +20°C showed a mean reduction of 10.4%). After 4 weeks of storage, there was a mean reduction of GHB concentrations higher than 20% at all storage temperatures. Ante-mortem urine samples showed a reduction of GHB levels higher than 10% after just 3 days of storage for samples kept at all tested temperatures. After 4 weeks of storage, there was a mean reduction of GHB concentrations higher than 25% at all storage temperatures.

CONCLUSIONS: According to our findings, it would be useful to perform GHB analysis both in blood and urine specimens within 3 days of sampling and the specimens should be stored at –20°C or 4°C in order to avoid instability issues.

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