A comprehensive study on the variations in urinary concentrations of endogenous gamma-hydroxybutyrate (GHB)

This study was designed to supplement previous attempts to establish an accurate range of normal endogenous gamma-hydroxybutyrate (GHB) concentrations in random antemortem urine samples. Furthermore, its purpose was to ascertain the effect of gender, race, age, medications, and select medical conditions on endogenous concentrations of GHB in urine and the proposed endogenous urinary GHB cutoff of 10 μg/mL. Urine samples (n = 207) were provided by subjects who reported that they had never used GHB. As part of the collection process, subjects also completed a short survey to collect information about gender, race, age, orally ingested medications, and select medical conditions. All specimens were analyzed in duplicate for the presence of endogenous GHB using a previously reported headspace gas chromatography-mass spectrometry method. The data were analyzed for tendencies among different population groups. GHB concentrations ranged from 0.00 to 2.70 μg/mL in all specimens, with a median concentration of 0.24 μg/mL. Males (n = 130) had an average endogenous GHB concentration of 0.27 μg/mL (0.00-2.70 μg/mL), whereas females (n = 77) averaged 0.29 μg/mL (0.00-0.98 μg/mL). Select medical conditions and participants' race, age ranges, and medications that were used within 48 h prior to collection were also evaluated. We believe this to be the most comprehensive study on endogenous GHB concentrations in urine to date. The results of this study will aid the interpretation of low GHB concentrations measured in urine samples, particularly in investigations of drug-facilitated crimes.