Urinary γ-hydroxybutyrate concentrations in 1126 female subjects.

γ-Hydroxybutyrate (GHB) and its metabolic precursor γ-butyrolactone (GBL) are often implicated in cases of drug-facilitated sexual assault (DFSA), although definitive confirmation of GHB/GBL ingestion is complicated by GHB's endogenous nature and rapid elimination following ingestion. Multiple studies have attempted to establish a discriminant limit (generally 10 mg/L) above which urinary GHB concentrations can be considered consistent with GHB/GBL consumption. To supplement the currently available data, a rapid gas chromatography-mass spectrometry method was developed and validated for the analysis of GHB (following acidic conversion to GBL) and used to analyze urine samples collected from 1126 women (mean = 0.84 mg/L, median = 0.68 mg/L, range = 0.00-5.5 mg/L). GHB concentrations were shown to be independent of urinary pH (within the range 4.6-9.3), age (within the range 18-35 years), body mass index (within the range 13.8-36.3), and race. Adjusting GHB concentrations with respect to urinary specific gravity had little effect on the mean value (0.91 mg/L) and range (0.0-7.76 mg/L), although a statistically significant trend of increasing GHB concentration with specific gravity could be observed. Our results can be taken to offer further support for the 10 mg/L discriminant limit for GHB administration in antemortem urine samples.