A study of urinary endogenous gamma-hydroxybutyrate (GHB) levels

In recent years, the use of gamma-hydroxybutyrate (GHB), as a recreational drug has prompted forensic toxicology laboratories to incorporate the analysis for GHB into their routine screening procedures. GHB, being a natural occurring constituent of the human body, presents a challenge for forensic toxicologists in that endogenous levels and exogenous levels of GHB need to be differentiated in case samples. This study was designed to determine typical urinary endogenous levels of GHB in humans based on the analysis of urine samples voluntarily provided by 55 male and female subjects ranging in age from 6 to 59 years. All samples were initially screened for the presence of GHB utilizing a hydrolysis method designed to quantitatively convert the GHB in urine samples to gamma-butyrolactone (GBL) followed by the liquid-liquid extraction and analysis of any GBL present by gas chromatography-mass spectrometry (GC-MS). As a confirmation test, samples were then extracted by a solid-phase extraction technique, derivatized to GHB di-TMS, and analyzed by GC-MS. The median concentration determined for the 55 subjects was 1.3 mg/mL (mean = 1.65 microg/mL, range 0.9 microg/mL to 3.5 microg/mL, standard deviation 0.68 microg/mL). The results of this study confirm the previously suggested cutoff of 10 microg/mL for routine forensic analyses.